White dwarfs often show signs of metals in their spectra, providing evidence that these evolved stars have accreted planetary material. Could white dwarf spectra also provide evidence for technological activity in these star systems?

A Record of Planets Past

When a Sun-like star reaches the end of its hydrogen-burning lifetime, it first puffs up into a red giant before exposing its white-hot core, which evolves into a white dwarf. This dramatic transition shakes up any planets that happened to be orbiting the star, and some close-in planets may end up crumbling apart, their rubbly remains peppering the surface of the white dwarf.

So far, astronomers have found hundreds of white dwarfs that appear to be polluted with heavy elements from their destroyed planets. These observations provide a valuable look into the bulk compositions of planetary materials outside our solar system. They may also provide a way to detect patterns of chemical abundances that are not natural, resulting from technological processes like industrial refining or the creation of alloys — in other words, a technosignature that is evidence of not just life, but technologically advanced life.

Seeking Signs of Technology

A team led by Bo-Lun Huang (黄博伦) from Beijing Normal University recently investigated whether there is evidence for chemical technosignatures in the current sample of polluted white dwarfs. Huang and collaborators began their investigation with a catalog containing 697 measurements of white dwarfs with metals in their spectra. They applied Bayesian statistical methods to weigh the hypothesis that the chemical makeup of these white dwarfs is entirely natural against the possibility that they contain a blend of natural and technologically altered material.

The team used thousands of chemical abundance measurements from meteorites as a reference for the natural bulk composition of planetary material. For the mixture of natural and processed material, they combined the meteorite reference material with a template that is metal-rich and silicate-poor, with enhanced amounts of iron, nickel, chromium, and manganese.

No Strong Evidence, but a Path Forward

Ultimately, Huang’s team found that strong statistical support for the existence of technological processes was uncommon, though there were certain measurements in their sample of white dwarfs that were difficult to reconcile with a solely natural model.

Perhaps unsurprisingly, the team also found that the quality of the chemical abundance measurements affected the constraining power of the observation; some white dwarfs had upper limits for just a few elements, while others had definitive detections of many elements. They found that the most discerning observations recorded iron, magnesium, chromium, and titanium, plus either nickel, silicon, or sodium.

While this work didn’t dredge up firm evidence for technological activity, it provides a jumping-off point for future searches. The handful of white dwarfs in this sample that were fit poorly by a purely natural model could be compared against other technosignature models or targeted with high-resolution spectroscopy. Future measurements of iron and magnesium in polluted white dwarfs may be useful as a preliminary screening tool, helping to pick out intriguing targets for follow-up observations.

Citation

“A Calibrated Bayesian Search for Potential Chemical Technosignatures in Polluted White Dwarfs,” Bo-Lun Huang et al 2026 ApJ 1006 9. doi:10.3847/1538-4357/ae742c

The post Seeking Technosignatures in Polluted White Dwarfs appeared first on AAS Nova.

Editor’s Note: Astrobites is a graduate-student-run organization that digests astrophysical literature for undergraduate students. As part of the partnership between the AAS and astrobites, we occasionally repost astrobites content here at AAS Nova. We hope you enjoy this post from astrobites; the original can be viewed at astrobites.org.

Title: Carbon Cycle Imbalances on Arid Terrestrial Planets with Implications for Venus
Authors: Haskelle T. White-Gianella and Joshua Krissansen-Totton
Authors’ Institution: University of Washington
Status: Published in PSJ

The Carbon-Cycle Thermostat

When discussing the habitability of planets, we usually focus on the habitable zone, the region around a star where a planet can host a temperature suitable for supporting liquid water on its surface. Yet, being in the right place doesn’t necessarily guarantee that a planet will be habitable.

A planet also needs the right atmospheric composition to sustain the necessary temperatures for hosting liquid water. A key mechanism found on Earth for maintaining this composition is the geologic carbon cycle, which acts as a built-in climate control system. This cycle begins with volcanic eruptions releasing carbon dioxide (CO₂₎, which then dissolves in rainwater and forms a weak acid that weathers rocks on continents. The weathering products wash into oceans, where they form carbonate rocks, locking carbon away. Eventually, plate tectonics recycles some of that carbon back to volcanoes. The weathering process works faster when the planet is warmer, thus regulating the amount of CO₂ and stabilizing the climate over long periods of time (but it should be noted that it can take up to a few hundred thousand years to rebalance this slow carbon cycle through the weathering process).

An important caveat is that the weathering process requires sufficient liquid water on the planet’s surface, so what happens in the case for planets with shallower oceans? Low-mass M dwarfs, the most common type of star found in the galaxy, are expected to host less-massive disks and therefore lower water inventories for forming planets. If more “dry” planets are indeed a more likely outcome of planet formation, we’d want to know how their arid conditions influence their long-term evolution and habitability.

Creating Carbon-Tracking Models

The authors built a model that tracks how water and CO₂ move between a planet’s interior, oceans, and atmosphere over 4.5 billion years. The model notably includes the following:

• A sophisticated weathering model that accounts for how runoff can limit rock weathering, improving upon previous models that only included a temperature dependence on weathering
• Wind-driven evaporation limits that influence the amount of water evaporation in addition to sunlight-driven evaporation
• Multiple deep water cycle parameterizations that explore how water moves between the interior and the surface

The model tests for four initial surface water inventories (0.1%, 1%, 10%, and 100% of Earth’s oceans) and then simulates how the surface water, atmosphere, and climate evolve over time.

A Critical Water Threshold

The models reveal that planets require at least 20–50% of Earth’s ocean mass to maintain a balanced carbon cycle. Below this threshold, the carbon cycle becomes unbalanced, leading to devastating consequences for habitability (Figure 1).

For the more arid planets, models reveal a concerning runaway process. Limited surface water reduces precipitation and slows rock weathering. Weathering cannot keep up with volcanic CO₂ release, causing CO₂ buildup and warming of the atmosphere. The cycle repeats, driving runaway warming until all water evaporates.

Important Implications (Within and Outside Our Solar System)

Looking within the solar system, the results offer an explanation for how a potentially habitable Venus could have transitioned into its current inhospitable state. If Venus had formed with an initial water inventory below this critical threshold of 20–50% of Earth’s ocean mass, then its carbon cycle would have become unbalanced, creating the CO₂ inferno seen on Venus today.

In future exoplanet studies, telescopes like the Habitable Worlds Observatory might detect ocean glint (specular reflection from liquid water) or measure land fraction from light curves. Finding a planet in the habitable zone but with limited ocean coverage would likely be bad news, as the planet could be quietly losing its grip on habitability. Astronomers may want to be more careful when looking at seemingly promising planets within their habitable zones.

Original astrobite edited by Natalie Price.

About the author, Jared Bull:

I am a 2nd-year PhD student at Johns Hopkins University. I study brown-dwarf variability and am interested in using time-series observations to uncover dynamic processes within their atmospheres. In my free time I like to read, cook, and do astrophotography.

The post Can Arid Planets Keep Their Cool? appeared first on AAS Nova.

Many observations of solar flares suffer from saturation and blooming, causing crucial information to be lost. Researchers recently validated a technique for retrieving information from saturated flare images, unlocking a treasure trove of powerful solar flares for examination.

Solutions for Saturation

Since 2010, the Atmospheric Imaging Assembly (AIA) on the Solar Dynamics Observatory (SDO) has been capturing nearly continuous extreme-ultraviolet images of the Sun’s disk, revealing our star’s dramatic high-energy behavior. Though SDO/AIA’s observations have transformed our understanding of the Sun’s activity, they have limitations: powerful solar flares can saturate the detector, spilling charge into nearby pixels.

This saturation and overflow compromises our ability to study the most energetic solar flares — but the “lost” information may actually be recoverable. When light from an intense flare enters SDO’s instruments, not all of it pools in the saturated region of the detector: some of the light is diffracted by the optics, and by mathematically inverting this pattern of diffracted light, researchers can attempt to extract the encoded information about the saturated region. Researchers have used this technique for more than a decade, but options for validating the results were limited until now.

Solar Orbiter Lends a Hand

Launched almost 10 years to the day after SDO, the Solar Orbiter spacecraft provides an excellent opportunity to test inversion techniques for recovering information from saturated solar images. Solar Orbiter’s Extreme Ultraviolet Imager snaps brief photos of the Sun at a rapid cadence, and its images remain unsaturated even when faced with energetic solar flares.

As described in a recent research article by Sabrina Guastavino (University of Genoa; Italian National Institute for Astrophysics) and collaborators, the ideal setup for testing the inversion technique arose on 19 March 2024, when SDO and Solar Orbiter both viewed a solar flare while separated by just 1 degree in longitude.

Guastavino’s team aligned and reprojected the data, accounting for the slightly different viewing angles of the two spacecraft, then applied an algorithm called Adaptive SE-DESAT to reconstruct the flux within the saturated portion of the SDO image. The team compared the desaturated SDO images to the unsaturated Solar Orbiter images over the course of the flare, finding the same flare morphology and similar time evolution between the two data sets.

A Treasure Trove of Desaturated Data

Overall, these results demonstrate the effectiveness of the inversion technique, though Guastavino and coauthors noted that improvements could be made during the impulsive phase of the flare, when the emission is increasing. The team identified several reasons why the results may not match during this phase, including rapid evolution of the flare during individual exposures.

Despite these areas that require further attention, the validation of this technique unlocks 16 years of solar flare observations from SDO. This especially enhances our sample of powerful solar flares, increasing the available records of the most energetic solar flares by orders of magnitude.

Citation

“Validation of an Extreme-Ultraviolet Desaturation Technique for the Atmospheric Imaging Assembly on Board the Solar Dynamics Observatory Using Observations from the Extreme Ultraviolet Imager on Board Solar Orbiter,” Sabrina Guastavino et al 2026 ApJL 1005 L50. doi:10.3847/2041-8213/ae7d2e

The post When the Spacecraft Align: Rescuing Saturated Images of Solar Flares appeared first on AAS Nova.

NASA is once again sending scientific missions to the Moon. But under the new commercial framework for getting there, researchers need to invent a new method for how to pick where to land.

A New Process for Picking Sites

NASA’s Commercial Lunar Payload Services program is a bold innovation in organizing robotic missions to the Moon. Under this model, rather than keeping the mission process entirely in-house, the agency selects the scientific mission they want to support then simply buys a ride to the lunar surface from a commercial vendor. But, how do you pick a landing site before you know exactly how you’re getting there?

The Lunar Vulkan Imaging and Spectroscopy Explorer (Lunar-VISE) mission, set to launch in mid-2028, was one of the first programs to go through this new landing site selection process. After being officially selected in 2022, the team had just nine months to nail down exactly where their mission should touch down. A recent article led by Jean-Pierre Williams (University of California, Los Angeles) detailed exactly how the team accomplished this task and presented some lessons they learned along the way.

No Parking Lots on the Moon

Picking a landing site is no small task: for context, selecting the landing sites for each of the most recent Mars rovers took five years and multiple community workshops. The Lunar-VISE team therefore took a streamlined and logic-driven approach. They started by explicitly laying out their science objectives: Lunar-VISE’s purpose is to investigate some strangely silicate-rich volcanic formations called the Gruithuisen domes, so they had to land either on or near those. They also had to have access to boulders that were excavated from deep within the domes during a crater formation event, so they had to pick a spot with boulders relatively nearby.

In addition to objectives, they also laid out a slew of constraints. Although they needed boulders nearby, they couldn’t have too many boulders, or any particularly large boulders, since those could pose hazards for landing. There also couldn’t be any steep slopes in the field. Most of the area had to maintain a line of sight with a supporting orbiter for communications, so they couldn’t set down near any ridges. Also, they had to consider how the terrain would cast shadows as the lunar day progressed, since they didn’t want their mission cut short by freezing temperatures and a lack of solar power. As the team quipped, “many interesting, high-science value locations on the Moon may not be in proverbial ‘parking lots.'”

By combing through archival data and working with the team that operates the Lunar Reconnaissance Orbiter Camera, a key asset for making detailed maps of the Moon, the researchers found the perfect spot: alongside a 190-meter-diameter crater named Mareta. This feature is named after Mareta West, one of the first female planetary geologists at the United States Geological Survey and the scientist who selected the landing site for Apollo 11’s historic touchdown.

In addition to presenting their landing site, the researchers offered a handful of lessons to others who may someday be in the fortunate and thrilling position of needing to pick a landing spot on the Moon. For one, they urged teams to coordinate with the Lunar Reconnaissance Orbiter specialists as early as possible, since processing the imaging data for lander-quality maps is a specialized and intensive task. For another, they recommended that all of the software tools used be made publicly available so that future missions don’t need to duplicate their work.

As this article laid out, the Commercial Lunar Payload Services program and Lunar-VISE take us one step closer to making missions to the Moon routine — but we’re still figuring out exactly how to do that.

Citation

“Lunar-VISE Landing Site Selection and Characterization at Mons Gruithuisen Gamma,” Jean-Pierre Williams et al 2026 Planet. Sci. J. 7 161. doi:10.3847/PSJ/ae7d2c

The post Putting the Landing Site Before the Lander appeared first on AAS Nova.

Do all star-forming regions birth stars with the same distribution of masses? Theory suggests that they do not, but researchers often assume they do for simplicity. Now, ultra-precise observations from Gaia have demonstrated that the initial mass function varies across star clusters in the Milky Way.

A Universal Initial Mass Function?

When a molecular cloud fragments, collapses, and births a star cluster, how many stars form, and what are their masses? The answer to that question is what astronomers term the initial mass function, or IMF: the distribution of masses of stars born in a cluster.

The IMF is important in many areas of astronomy, and it’s relied on especially heavily in studies of distant galaxies. The light from these galaxies is dominated by high-mass stars, with the emission from lower-mass stars lost in the glare, so astronomers must use the IMF to reconstruct the stellar populations of these far-off locales.

Though theory suggests that the IMF should vary with factors like temperature and metallicity, demonstrating these variations has been difficult, even within our own galaxy. Because of this, researchers often adopt a universal IMF drawn from observations of star clusters in the Milky Way. But is the IMF truly universal?

The More the Slope Changes, the More the Break Mass Stays the Same

Determining whether the IMF is universal is more complicated than simply comparing the stars in one cluster to those in another. That’s because what astronomers measure in present-day star clusters is not the initial mass function, but a version of the IMF that has been skewed by millions to billions of years of evolution; over time, high-mass stars die and low-mass stars get ejected, warping the shape of the mass function.

However, as demonstrated in a recent research article led by Charles L. Steinhardt (University of Missouri), certain aspects of the IMF may remain unchanged as clusters evolve. When the mass function of a star cluster is described using a broken power law (commonly called a “Kroupa-like” IMF in reference to work by Pavel Kroupa), the slopes of the power-law segments are affected by stellar evolution and dynamical interactions. Crucially, these effects appear not to alter the break mass — the mass at which the IMF transitions from one slope to another. Therefore, differences in the break mass from cluster to cluster reflect differences in the underlying IMF rather than the stellar and dynamical evolution of the clusters.

Insights from Gaia

Thanks to the Gaia spacecraft, which made precise observations of more than 2 billion stars in the Milky Way and beyond, it’s now possible to measure and compare the break masses of individual star clusters. Out of an initial catalog of 7,167 Milky Way clusters observed with Gaia, Steinhardt’s team selected just 110 that were of high enough quality and contained a sufficient number of stars to measure cluster break masses accurately.

The team found that the break mass differs considerably between the clusters in their sample, showing that the IMF is not universal. The observed variety of break masses appears to be linked to the age of the cluster, but instead of reflecting the impact of stellar and dynamical evolution — which have no effect on the break mass — these differences reflect the properties of the clouds in which the clusters were born. This implies that the properties of star-forming clouds in the Milky Way have, on average, changed over cosmic time. Thus, a star cluster that formed billions of years ago would have had a different IMF than one forming today.

This finding has implications for studies of high-redshift galaxies, where the properties of star-forming clouds are markedly different from those in the Milky Way. Going forward, Steinhardt and coauthors recommend developing a flexible parameterization of the IMF to capture how this critical function behaves in environments vastly different from our own.

Citation

“Direct Evidence for Stellar Initial Mass Function Variation in the Milky Way,” Charles L. Steinhardt et al 2026 ApJL 1005 L40. doi:10.3847/2041-8213/ae7444

The post Gaia Data Show That the Initial Mass Function Is Not Universal appeared first on AAS Nova.

Editor’s Note: Astrobites is a graduate-student-run organization that digests astrophysical literature for undergraduate students. As part of the partnership between the AAS and astrobites, we occasionally repost astrobites content here at AAS Nova. We hope you enjoy this post from astrobites; the original can be viewed at astrobites.org.

Title: MAGAZ3NE: Confirming Dust Deficiency and Quiescent Nature of Ultramassive Galaxies at 3 < z < 4 with ALMA Observations
Authors: Wenjun Chang et al.
First Author’s Institution: University of California, Riverside
Status: Published in ApJ

Distant galaxies offer a unique window into how stars, gas, and dust evolve over cosmic time. Tracing this evolution requires understanding not only how galaxies form, but also how and when they stop forming stars, a process known as quenching. Understanding how, when, and why galaxies quench is a fundamental question in astrophysics, and one that requires observations of star-forming, quenching, and fully quenched galaxies alike. Unfortunately, one complication is that identifying truly quenched galaxies is challenging: galaxies that appear “dead” may instead be actively forming stars, hidden behind a thick veil of dust.

In today’s article, the authors use observations from the Atacama Large Millimetre/submillimetre Array (ALMA) to investigate five ultramassive galaxies at redshifts, z, between 3 and 4, and ask a deceptively simple question: are these massive red galaxies genuinely quenched, or are they secretly forming stars behind the scenes?

Meet the Suspects: Ultramassive Galaxies at the Edge of Cosmic Noon

The five galaxies in this study are drawn from the Massive Ancient Galaxies at z > 3 NEar-infrared (MAGAZ3NE) survey, which targets some of the most massive galaxies known at early cosmic times. All five have stellar masses exceeding 100 billion solar masses and have been confirmed at z > 3. At these redshifts, we are observing the galaxies as they were when the universe was less than 2 billion years old. This is just before an epoch known as cosmic noon, when star formation across the universe reached its peak.

These galaxies also benefit from extensive multiwavelength observations from a range of observatories, including the ground-based Visible and Infrared Survey Telescope for Astronomy and the Spitzer Space Telescope. By combining imaging across wavelengths from the ultraviolet to the near-infrared, astronomers can measure the “colours” of galaxies and use these colours to infer the galaxies’ star-forming activity.

Galaxies that have quenched their star formation are dominated by older stellar populations, which makes them appear red (hence why they are often referred to as “red and dead” galaxies). However, dust can redden galaxies in a similar way by absorbing blue light and re-emitting it at longer wavelengths — meaning that a dusty, star-forming galaxy can easily masquerade as a quenched one. To uncover any hidden star formation, the authors turn to ALMA to search for far-infrared dust emission. The sample of galaxies investigated with ALMA is shown in Figure 1.

ALMA on the Scene

ALMA observes light at sub-millimetre wavelengths, which at these redshifts traces emission from star-forming regions that are obscured by dust. Of the five ultramassive galaxies in this sample, only one is detected with ALMA. Even when the remaining four galaxies are stacked together, no dust emission is recovered, indicating that if any dust is present, it must be extremely faint.

To better quantify what these ALMA non-detections imply, the authors perform spectral energy distribution fitting (see a recent overview bite on spectral energy distribution fitting) using the Code Investigating GALaxy Emission, or CIGALE, a code that enforces energy balance between absorbed starlight and dust emission to estimate physical properties such as a galaxy’s star formation rate and dust content. With the ALMA constraints included, all five galaxies are found to lie more than 10 times below the star-forming main sequence. Even the single ALMA-detected galaxy remains formally quenched, showing only weak residual star formation.

In other words, these galaxies really are dead (or at least extremely dormant).

Extremely Dust-Poor Galaxies

The spectral energy distribution fitting also allows the authors to measure how much dust these galaxies contain relative to their stellar mass. This ratio provides a simple but powerful way to assess how much interstellar material remains in a galaxy — and therefore how much fuel is left for future star formation.

Three of the five ultramassive galaxies have ratios of M_dust/M_star < 10^-4 (Figure 2), placing them among the most dust-poor quenched galaxies confirmed at z > 3. The lone galaxy detected by ALMA contains slightly more dust, with M_dust/M_star = 10^-3, but even this is far below what would be expected for an actively star-forming galaxy. For comparison, typical star-forming galaxies at similar stellar masses host more than 100 times more dust.

These results raise important questions about how galaxies can become ultramassive, quenched, and nearly dust-free within the first two billion years of cosmic history.

For now, ALMA has delivered a clear answer to the question of “dead or in disguise?”: at least some candidate ultramassive galaxies in the early universe really are quenched, and they are strikingly dust poor. By ruling out the dusty impostor scenario, this study shows that deep ALMA observations can cleanly distinguish genuinely quenched galaxies from dusty star-forming ones, even at the highest stellar masses and earliest cosmic times. How these galaxies lost their dust remains an open question, but one thing is clear: by the time cosmic noon arrived, some galaxies had already finished forming stars and quietly faded into dormancy.

Original astrobite edited by Viviana Cáceres.

About the author, Lucie Rowland:

I’m a fourth (and final!) year PhD student at Leiden Observatory in the Netherlands, studying massive, star forming galaxies in the early universe with ALMA and JWST. It’s a really exciting time to be interested in astronomy, so I hope to make groundbreaking new research more accessible!

The post Distant Galaxies: Dead or in Disguise? appeared first on AAS Nova.

The Bullet Cluster is best known for being considered a “smoking gun” for the existence of dark matter, but even a famous galaxy cluster like this one has its secrets. For more than two decades, different measurements of the merging clusters’ dynamical mass ratio have yielded vastly different results. In a recent research article, Boseong Young Cho (Yonsei University) and collaborators used data from JWST and the Dark Energy Camera to revisit the Bullet Cluster and measure its mass ratio using new data. The image above shows a near-infrared view of the Bullet Cluster from JWST, with an overlay of mass contours derived from gravitational-lensing measurements. The team’s analysis assigned a mass of 1.5 quadrillion solar masses for the main cluster (on the left side of the image above), and a mass of 150 trillion solar masses for the subcluster. This suggests a mass ratio of roughly 10, which matches the value supported by hydrodynamical simulations and cements the event as a minor merger. The team also identified three distinct cluster halos (two in the main cluster and one in the subcluster), providing an important constraint on the cluster configuration for future modeling. To learn more about this investigation of the Bullet Cluster, be sure to check out the full research article linked below!

Citation

“Joint JWST–DECam Lensing Reveals that the Bullet Cluster Is a Minor Merger,” Boseong Young Cho et al 2026 ApJ 1005 28. doi:10.3847/1538-4357/ae6a90

The post Featured Image: A Mass Mystery in the Bullet Cluster appeared first on AAS Nova.

Stellar rotation is a crucial aspect of not only stellar evolution but also exoplanet science, and a recent study has built the largest catalog of stellar rotation periods to date.

Stellar Opportunities with TESS

Since its launch in 2018, the Transiting Exoplanet Survey Satellite (TESS) has scoured the sky, searching for the signature recurring dip in starlight caused by planetary companions. While the primary goal of TESS is to discover exoplanets, the satellite’s mapping of the entire sky has created a rich database of high-quality photometry for millions of stars. These observations offer ample opportunity for scientists to study stellar properties and behavior across the Milky Way.

In particular, stellar rotation is a key property that traces a star’s age, magnetic activity, and internal structure. For exoplanet science, stellar rotation is both a help and a hindrance: it allows us to study how exoplanets may evolve over time with their host stars, but stellar activity can mimic or drown out planet signals, making them harder to detect. A few studies have investigated stellar rotation periods with TESS, looking at specific star clusters and known planet hosts. To date, however, no existing study has produced a larger catalog of TESS rotation periods — a product that would provide a wealth of information for both exoplanet and stellar evolution science.

Creating a Catalog

Seeking to build a flux- and distance-limited catalog of TESS rotation periods, Andrew W. Boyle (The University of North Carolina at Chapel Hill) and collaborators used TESS full-frame images to survey the local neighborhood for stellar variability. To measure reliable stellar rotation periods for as large and diverse a sample as possible, the authors made selection cuts in brightness, distance, and data availability to build a target sample of 7,481,412 stars. They generated light curves for each observation of each star and searched them for periodicity, or repeated variation in brightness.

Not all brightness variations present in a star’s light curve are due to stellar variability — instrumental systematics and artifacts from the spacecraft’s orbital period can produce periodic variability. To combat this, the authors created a classification algorithm to select sources whose periodicity is most likely due to true stellar variability rather than instrumental or observational effects. Pairing this classification with some additional validation criteria, the authors built the TESS All-Sky Rotation Survey (TARS), a catalog of periods for 1,046,317 stars within about 1,600 light-years of our Sun.

Implications of TARS

Looking more finely at the TARS catalog, the authors provided additional quality cuts to remove other potential sources of stellar variability like binary companions or pulsations. The authors estimated that roughly 93% of their measured periods are due to stellar rotation, which expands the number of stars with known rotation periods by a factor of 2.3 within about 325 light-years and by a factor of 4.0 within about 1,600 light-years. As the largest homogeneous catalog of stellar rotation periods to date, TARS lays the groundwork for studies of stellar evolution, exoplanet discovery and evolution, and even Milky Way structure. For example, the authors found that when mapping the fast-rotating, typically younger stars in TARS, the location of young stellar associations in the local neighborhood became significantly clearer. This underscores the importance of this catalog for a range of science goals, and future work will only improve upon the data provided by TARS.

Citation

“The TESS All-Sky Rotation Survey: Periods for 1,046,317 Stars within 500 pc,” Andrew W. Boyle et al 2026 ApJS 284 75. doi:10.3847/1538-4365/ae6657

The post A New Catalog of Stellar Rotation Periods for Over a Million Stars appeared first on AAS Nova.

One of the biggest discoveries from JWST’s tenure is a population of compact reddish objects nicknamed “little red dots.” Numerous theories have been proposed to explain the small sizes, high luminosities, and characteristic “V”-shaped spectra of these objects, and today we’ll examine two recent research articles that have explored the identity of the universe’s most mysterious inhabitants.

Red Dot, Blue Dot

You can tell a lot about a person by looking at their friends — and the same might be true for little red dots. A team led by Josephine Baggen (Yale University) examined a sample of 83 little red dots imaged with JWST. They found that 43% of the little red dots in this sample had a little blue companion: an ultraviolet-bright object within a projected separation of 1,630–16,300 light-years. The brightest little red dots were even more likely to have a blue companion; 80% of the brightest objects in the sample were paired up.

Baggen’s team set out to test the hypothesis that these red–blue pairs are fundamentally linked rather than coincidental. Under this hypothesis, the ultraviolet-bright blue companions were assembled first. The ultraviolet radiation from these objects suppressed the cooling of molecular hydrogen in pristine gas clouds in the early universe, causing the gas to skip the usual star-forming process and instead form a massive compact object such as a black hole star, supermassive star, or quasi-star — which we see as a little red dot.

Baggen and coauthors investigated whether the ultraviolet radiation from the blue companions is strong enough to have triggered this transformation. The team used spectral energy distribution modeling to determine the luminosities of the blue companions from 91.2 to 111 nanometers. This analysis showed that the radiation from the blue companions is equal to or greater than the threshold necessary to encourage the direct collapse of a gas cloud into a massive compact object.

If little red dots form thanks to their little blue companions, that would imply that every little red dot has or had such a companion. Though little blue companions weren’t so universal in the sample used in this work, the team noted that their analysis techniques, combined with observational limitations and other factors, likely yielded a smaller number of blue companions than are actually present. Further simulations exploring the collapse of pristine gas clouds into massive compact objects and high-resolution spectroscopic observations of little red dots can illuminate the potential link between these objects.

Little Red Dots as Young Globular Clusters

John Chisholm (The University of Texas at Austin) and collaborators hypothesized that little red dots represent a brief phase in the formation of globular clusters. In this hypothesis, the rest-frame ultraviolet emission of little red dots comes from the hot young stars of the newborn cluster, while the rest-frame optical emission comes from a single supermassive star at the cluster’s heart. Thus, in this framework, the little red dot phase lasts only as long as the fleeting lifespan of the supermassive star.

Chisholm’s team first showed that the spectrum of a young globular cluster with a supermassive star at its center is similar to the observed spectrum of a little red dot. But showing that the emission properties of globular clusters in formation and little red dots are similar is not enough — it’s also necessary to investigate whether the numbers and masses of these objects line up.

To do this, the team propagated the observed mass function of little red dots at a redshift of z = 7 forward in time to z = 0. This process accounted for the rapid evolution of the supermassive star into a black hole, as well as the evolution of and feedback from the massive stars in the cluster. Comparing the resulting mass function to the population of present-day globular clusters, the team found that the mass functions had very similar shapes, and the number densities of little red dots and globular clusters in the present day are estimated to be of the same order of magnitude: 0.1–0.3 Mpc^-3 and 0.8 Mpc^-3, respectively.

In addition to describing how the properties of globular clusters in formation match those of little red dots, Chisholm’s team outlined some testable predictions for this scenario, including formation timescales and chemical abundance patterns. If this hypothesis withstands further scrutiny, little red dots may provide a valuable look at the early years of some of our universe’s oldest star clusters.

Citation

“Connecting the Dots: UV-Bright Companions of Little Red Dots as Lyman–Werner Sources Enabling Direct-Collapse Black Hole Formation,” Josephine F. W. Baggen et al 2026 ApJL 1002 L4. doi:10.3847/2041-8213/ae58a5

“Little Red Dots as Globular Clusters in Formation,” John Chisholm et al 2026 ApJL 1004 L4. doi:10.3847/2041-8213/ae6dae

The post Two More Thoughts on Little Red Dots appeared first on AAS Nova.

Editor’s Note: Astrobites is a graduate-student-run organization that digests astrophysical literature for undergraduate students. As part of the partnership between the AAS and astrobites, we occasionally repost astrobites content here at AAS Nova. We hope you enjoy this post from astrobites; the original can be viewed at astrobites.org.

Title: The Wandering Supermassive Black Hole Powering the Off-Nuclear Tidal Disruption Event AT2024tvd
Authors: M. Guolo et al.
First Author’s Institution: Johns Hopkins University
Status: Published in ApJL

A Star Gets Eaten in the Wrong Neighborhood

We find supermassive black holes at the centers of most large galaxies. They end up there because of how galaxies form: as matter collapses and merges over time, material sinks to the gravitational center, and the black hole settles in.

So, what happens when we catch a star being ripped apart by a supermassive black hole that is not at the center of its galaxy?

That is exactly the puzzle posed by AT2024tvd, a tidal disruption event (TDE) spotted roughly 2,600 light-years from the center of a massive galaxy located 600 million light-years away from us (see Figure 1).

We see TDEs when a black hole tears apart a star that gets too close to it. It happens because the black hole’s gravity pulls harder on the near side of the star than the far side, stretching the star until it comes apart. The stellar debris then forms a hot accretion disk, a ring of material swirling around the black hole that spirals inward and releases a burst of electromagnetic energy across many wavelengths — from visible light to X-rays. These events are valuable to astronomers because they briefly light up black holes that would otherwise be invisible, giving us a rare window to measure their properties. Since supermassive black holes live at galactic centers, that is also where we expect TDEs to happen, which makes a TDE found away from a galactic center rare and puzzling. The galactic center is often called the nucleus of a galaxy, so astronomers refer to these displaced events as “off-nuclear” TDEs. AT2024tvd is only the third known off-nuclear TDE, and this research article makes a strong case that it is the most remarkable one yet.

Measuring Mass Using Light

To figure out the mass of the black hole responsible for AT2024tvd, the authors needed to get creative. You cannot weigh a black hole directly, so astronomers have to work backward from what they can see. The key idea is that a black hole’s mass controls how its accretion disk behaves. A more massive black hole produces a larger, cooler disk, while a less massive one produces a smaller, hotter disk. By measuring how bright the disk is at different wavelengths and how hot it gets, you can figure out how massive the black hole must be.

The authors did this by modeling the light the event produced across many wavelengths. They combined data from several telescopes: the Zwicky Transient Facility, the Neil Gehrels Swift Observatory, Pan-STARRS, and two rounds of high-quality X-ray data from XMM-Newton. TDE light curves go through different phases. The early flare in visible and ultraviolet light is bright but complicated, and the physical processes behind it are not fully understood. But after a few hundred days, TDEs settle into a quieter “plateau phase,” where the ultraviolet and visible light come directly from the accretion disk. At this stage, the emission follows well-understood physics, and astronomers can model it reliably.

The authors used a model called kerrSED, which describes the spectral energy distribution (SED) of a spinning black hole’s accretion disk (kerr). It accounts for the disk’s temperature, its physical size, the black hole’s spin (how fast it rotates), and the angle at which we are viewing the system. It also accounts for a process called Comptonization, where hot electrons near the black hole boost lower-energy photons (particles of light) up to X-ray energies. By fitting this model to the observed light at multiple wavelengths simultaneously, the authors could pin down the disk properties and extract the black hole mass. The result was a clean fit: the disk model alone could explain all the observed light during the plateau phase, with nothing significant left over (see Figure 2).

Not an Intermediate, but a Supermassive Black Hole

From their fit, the authors found a black hole mass of about one million solar masses. Black holes above about 100,000 solar masses are considered supermassive, while those below that threshold but above about 100 solar masses are called intermediate-mass black holes. So, this puts AT2024tvd in the supermassive category. This matters because the two previously known off-nuclear TDEs, called 3XMM J2150-05 and EP240222a, were both powered by intermediate-mass black holes. Those black holes were found inside small, dense collections of stars called ultra-compact dwarf galaxies that were orbiting larger host galaxies.

AT2024tvd is different. When the authors looked at deep images of the location where the TDE happened, they found no star cluster or small galaxy there. Whatever group of stars once surrounded this black hole has been almost entirely pulled apart by the gravity of the much larger parent galaxy. The ratio of the black hole’s mass to the mass of any remaining stars around it is extreme: greater than 3%, which is far above what we normally see. This is the signature of a “wandering” supermassive black hole, one that was brought in during a past galaxy merger and has been slowly sinking toward the center of its new host ever since, losing its surrounding stars along the way.

The authors compared AT2024tvd to other TDEs using established relationships between accretion disk properties and black hole mass (Figure 3). In terms of its disk temperature, luminosity, and inferred mass, AT2024tvd behaves like a typical nuclear TDE powered by a supermassive black hole. However, when placed on the black hole mass versus host stellar mass relation, it stands out as a strong outlier. The black hole mass is far too large for the small amount of surrounding stellar mass detected at its location.

The Big Picture

This discovery matters for several reasons. It shows that off-nuclear TDEs are not limited to intermediate-mass black holes sitting in small satellite galaxies. Some are powered by fully supermassive black holes that have been displaced from their original galactic centers. It also shows that TDE modeling, when done carefully during the plateau phase of the light curve (when the emission is dominated by well-understood accretion disk physics), can provide reliable black hole masses on its own, without assuming any relationship between the black hole and its host galaxy. This is particularly important for wandering black holes, where those relationships do not apply.

Looking ahead, upcoming surveys like Vera C. Rubin Observatory’s Legacy Survey of Space and Time are expected to find many more off-nuclear TDEs. Combined with X-ray follow-up from telescopes like XMM-Newton, these events could become our main tool for mapping out the population of displaced black holes in the nearby universe. One disrupted star at a time, we are starting to find black holes that theory told us should exist but that had, until now, stayed hidden.

Original astrobite edited by Kelsie Taylor and Veronika Dornan.

About the author, Serat Saad:

Serat is a first-year PhD student in astronomy at The Ohio State University. His research is on stellar and galactic dynamics, where he uses observational data to understand gravity. He also has interests in active galactic nuclei and tidal disruption events.

The post A Wandering Supermassive Black Hole Eating a Star appeared first on AAS Nova.

Microlensing surveys have discovered plenty of regular exoplanets, but more surprisingly, they’ve also turned up many solo Neptunes with no star nearby. New research suggests that first impressions might be deceiving, however, and that at least some of these planets might not be so alone: they just have a complicated family history.

An Abundance of Exo-Neptunes

There are simply too many Neptune-like exoplanets in our galaxy. Or at least that’s the current feeling astronomers get from gravitational microlensing surveys, which look for exoplanets during short-lived magnification events caused by chance alignments between stars. These surveys have now found about a dozen so-called “free-floating” planets, and while this doesn’t sound like that many, running the numbers reveals that this tiny sample implies that there are about two free-floating Neptune-size planets for every star in the galaxy.

The idea that there are more free-ranging Neptunes than stars is unsettling, and astronomers aren’t yet sure how this many planets ended up so isolated. It’s possible that these objects simply formed disconnected from any planetary system, but it’s unclear how something so small could collapse from the interstellar clouds that usually produce stellar-mass objects. It’s also possible that the planets formed around stars in the usual way, only to be later kicked out by some violent dynamical process — but this would either require too much time or too many giant planets capable of ejecting the lower-mass ones.

However, new research by Sam Hadden (Canadian Institute for Theoretical Astrophysics) and Yanqin Wu (University of Toronto) presents an alternative idea: what if at least some of these free-floating planets aren’t fully on their own, but instead remain estranged but weakly bound to their parent stars?

Simulated Scattering

Two celestial objects need to align nearly perfectly in order to create a microlensing pulse that we can detect. For an exoplanet orbiting a star, we should observe two of these pulses: one when the host star drifts in and out of alignment with a background star, and one when the nearby bound planet does the same. In the case of a free-floating planet, there’s only one pulse, and we therefore assume that there is no host star. Hadden and Wu noticed that since the alignment has to be so precise for microlensing to occur, it’s possible that a seemingly free-floating planet is simply widely separated from its host star, and the star managed to dodge the magnification effect. In other words, these planets might not be free floating at all, just on wide and eccentric orbits.

The researchers decided to test whether it’s possible to create these kinds of orbits via a known dynamical process called planet–planet scattering. As the name implies, during this process, planets that begin on orderly orbits around their parent star undergo a dramatic rearrangement as they jostle each other around through gravitational interactions. The researchers created two types of simulations: one with a collection of equal-mass planets, and another in which one planet dominates over a brood of smaller ones. After setting up the systems, they let the “dynamical havoc” proceed for a few hundred million years, then surveyed the aftermath.

They found that both types of simulations readily created the “detached” objects needed to mimic free-floating planets. In fact, the most common outcome was for two or three planets to be bullied into far-out orbits by a planet that then plunges onto a tight inner orbit extremely close to the star.

Though the authors caution that this process likely doesn’t explain all of the free-floating planets observed to date, this is an exciting model that would dramatically lower our estimates of the number of Neptunes roaming alone between the stars.

Citation

“Free Floating or Merely Detached?,” Sam Hadden and Yanqin Wu 2026 ApJ 1000 70. doi:10.3847/1538-4357/ae6508

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Fullerenes — a class of molecules composed entirely of interconnected carbon atoms — are the largest molecules definitively detected in space. Researchers using JWST to study a planetary nebula have found new spectral features from a fullerene composed of 60 carbon atoms, offering another way to study how these molecules form and survive in space.

Full of Fullerenes

The planetary nebula Tc 1 holds special significance in the field of astrochemistry. More than a decade ago, researchers using the Spitzer Space Telescope studied this wispy nebula illuminated by the core of a dead star. These observations led to the first confident identification of molecules called fullerenes in space. Fullerenes are large molecules constructed from interconnected rings of carbon atoms, forming hollow spheres, rugby-ball shapes, and long tubes. Spheroidal fullerenes, especially C₆₀, are commonly referred to as buckyballs.

Since that discovery, Tc 1 has been a hot spot for studies of buckyballs. However, researchers are still puzzling over how these large molecules form and survive in harsh space environments.

From Spitzer to JWST

Morgan Giese (The University of Western Ontario) and collaborators recently reported on the results of a JWST observing program that aimed to understand how fullerenes respond to changes in their environment. The team mapped the distribution of C₆₀ molecules at varying distances from the powerful ionizing radiation of Tc 1’s central star.

The team successfully spotted the emission features from the fullerene C₆₀ seen in earlier observations, but they also turned up something unexpected: a handful of prominent emission features from 3.5 to 5.2 microns that had not been reported previously.

Feature Presentation

What’s the source of these emission features? The distribution of the emission provides a strong clue: known spectral features from fullerenes C₆₀ and C₇₀ are concentrated in a narrow, bright ring around the center of the nebula, with diffuse emission suffusing the rest of the nebula — and the newfound spectral features follow the same distribution.

This evidence hints that C₆₀ or C₇₀ is the source of these new features, but Giese’s team took the investigation a step further. Using anharmonic quantum chemical calculations, they computed the spectrum of C₆₀‘s combination bands, which arise when multiple vibrational modes are excited at the same time. This is the first time this type of spectrum has been calculated for C₆₀, and the authors found good agreement between their computed spectrum and the JWST spectrum, providing further evidence that C₆₀ is the source of these bands.

Giese and coauthors found that 17% of the energy emitted by the C₆₀ molecules in Tc 1 is released in these  combination bands, suggesting that these features must be taken into account when modeling the cooling of C₆₀ molecules. The discovery of new fullerene spectral features also has implications for future studies of these molecules: since these features appear in a wavelength range where features from other complex molecules like polycyclic aromatic hydrocarbons are weak, these newly identified bands provide a promising way to spot and study fullerenes across space environments.

Citation

“Detection of C₆₀ Combination Bands in the Near-IR Spectrum of Tc 1,” Morgan M. Giese et al 2026 ApJL 1004 L32. doi:10.3847/2041-8213/ae76d5

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Editor’s Note: Astrobites is a graduate-student-run organization that digests astrophysical literature for undergraduate students. As part of the partnership between the AAS and astrobites, we occasionally repost astrobites content here at AAS Nova. We hope you enjoy this post from astrobites; the original can be viewed at astrobites.org.

Title: A GLIMPSE of Intermediate Mass Black Holes in the Epoch of Reionization: Witnessing the Descendants of Direct Collapse?
Authors: Qinyue Fei et al.
First Author’s Institution: University of Toronto
Status: Published in ApJ

In the late 2010s, astronomers were getting hints of something strange going on in the early universe. Using the most powerful telescopes on the ground, we were able to find black holes in the centers of some of the most distant galaxies. The light from these active galactic nuclei (AGNs) was emitted over 12 billion years ago, revealing conditions close to the beginning of cosmic time.

To an astronomer, that’s the mundane part. I’m only half joking — thousands of AGNs had already been identified in the previous half century. However, the most distant of these sources were startling because their central black holes appeared much more massive than expected. To be specific, we know how much mass black holes can start with, and we can write down equations to predict how quickly they should grow. The AGNs we observed seemed to violate these predictions. This raised some serious questions and was highlighted as a major point of inquiry to focus on going into the 2020s.

Then JWST launched, and the mystery grew deeper. No matter where we looked, enormous black holes kept cropping up in astonishing numbers. Astronomers who model the universe with equations and computer simulations have tried to explain these results, but this has been a serious challenge. Some researchers have broken the emergency glass and reached for a highly theoretical tool: the direct-collapse black hole. Unlike the normal pathway for forming black holes (the deaths of massive stars), this model suggests that an enormous cloud of gas could directly collapse into a black hole without forming a star at all. The resulting black holes could have as much mass as a hundred thousand Suns put together — orders of magnitude more than a “normal” black hole. Although this pathway can explain the presence of huge black holes so early in the universe’s history, we’ve never directly seen this happen, so for now it remains just a theoretical possibility.

However, if direct-collapse black holes were widespread at early times, there is one indirect signature we might be able to detect: a large population of intermediate-mass black holes with masses between a hundred thousand and a million times that of the Sun. If we can find such a population, we’ll have strong evidence for the direct-collapse model. Let’s go looking!

Intermediate Mass, Impossible Difficulty

Identifying intermediate-mass black holes requires a tricky combination of spectral resolution and sensitivity. Light from an object must be examined very finely in order to detect the telltale features of an intermediate-mass black hole. However, these sources are already quite faint, so spreading their emission this thin means that any potential signal is very likely to get lost in the noise.

The authors of today’s article use an unprecedented set of observations to leap over this hurdle and directly probe intermediate-mass black holes. They not only use the most sensitive spectroscopic instrument (NIRSpec) on the most powerful space telescope (JWST), but they take advantage of a phenomenon known as gravitational lensing.

According to Einstein’s general theory of relativity, gravity is the result of matter curving spacetime. Areas with more concentrated matter will experience stronger curvature. When an object traveling in a completely straight line moves through curved space, its path appears bent. This same effect happens to light. Intriguingly, a large concentration of matter can redirect diverging rays of light to a focus, acting like an enormous magnifying glass.

Astronomers take advantage of gravitational lensing by pointing telescopes at massive clusters of galaxies. The intense gravity of these regions can magnify sources in the background by tens or even hundreds of times. Galaxies that would be impossibly faint to see under normal conditions can thus be observed if they are strongly lensed, making this a powerful technique to examine otherwise hidden objects.

Putting Faint AGNs Under a Lens

The Galactic Legacy Infrared Mid-Plane Survey Extraordinaire (GLIMPSE) program took extremely powerful observations of a galaxy cluster called Abell S1063 using JWST. The long exposure time, combined with the lensing power of the cluster, allows extremely faint sources in the background to be seen in unprecedented detail. The researchers scoured the data to search for signs of active black hole growth in the observed galaxies. Specifically, they carefully studied the emission lines in the spectrum of each object.

Normally, emission lines appear narrow. However, gas surrounding a massive black hole circulates at rapid speeds. A phenomenon known as the Doppler effect then comes into play. This is the same effect responsible for the characteristic rise and fall in the pitch of a siren from an emergency vehicle passing by. Emission from gas moving toward our line of sight appears bluer than it otherwise would, and gas moving away from us appears redshifted. The net effect is that a single emission line is widened, and we see characteristic “broad wings.” The width of the emission line can be used to estimate the mass of the central black hole, where broader wings imply a more massive black hole.

The researchers uncover 10 AGNs that display broadened Balmer series lines. Strikingly, they estimate that these galaxies have central black holes with masses as low as 400,000 times that of the Sun. While that might sound like a lot, it’s practically nothing compared to the monstrous 100-million-solar-mass black holes that JWST consistently turns up in other studies. Detecting such lightweight black holes, pushing into the realm of intermediate-mass black holes, is only possible due to the incredible sensitivity of these observations.

The researchers also compute what’s known as the black hole mass function. This is a measure of how many black holes exist at each mass. In other words, the black hole mass function measures how common lightweight black holes are compared to heavy ones. The mass function computed in this work and several other points of comparison are shown in Figure 1.

Because the AGNs analyzed in today’s article host central black holes with much lower masses than any that have been observed in the past (at this early time in the universe), the authors are able to probe a completely new region of the black hole mass function. As seen in Figure 1, the leftmost red hexagon (lowest-mass data point) deviates from the roughly straight line traced by the other data points. This suggests that there are substantially more black holes with a few hundred thousand solar masses than previously expected.

Amazingly, this is exactly the measurement you would get if direct-collapse black holes (the hypothetical kind of massive black holes mentioned earlier in this article) were common in the early universe. If you scatter huge seeds across a large field, then you shouldn’t be surprised to see a sea of barely larger plants a few months later. Likewise, since these black holes start off so massive, they only need to grow a tiny bit to reach the threshold of that first red hexagon.

So is this proof that the early universe was filled with direct-collapse black holes, with this study probing the tip of an astonishing iceberg? It’s too early to tell for sure. While this is certainly an exciting result that sheds light on a previously unexplored population of objects, one can only do so much with a sample size of 10. More follow-up observations will be needed to measure the black hole mass function more precisely. Still, it’s amazing to think how much has changed in just a few years. JWST continues to provide unprecedented insight into some of the most breathtaking questions in all of astronomy.

Original astrobite edited by Tori Bonidie.

About the author, Ansh Gupta:

I’m an astronomy graduate student at the University of Texas at Austin working with Steven Finkelstein. I use data from JWST to study the formation and growth of the first galaxies and black holes in the universe. In my spare time, I enjoy playing piano, reading, and making YouTube videos.

The post Black Holes Reveal Their Seeds appeared first on AAS Nova.

The image above shows a newly discovered molecular cloud. This cloud was discovered through the Milky Way Imaging Scroll Painting project, which uses a 13.7-meter millimeter telescope to survey molecular clouds in our galaxy. Xuepeng Chen (Purple Mountain Observatory; University of Science and Technology of China) and collaborators came upon this cloud in survey data from a region of the Milky Way opposite the galactic center. The newfound cloud is roughly 5,400 light-years away, spans an area of 245 by 294 light-years, and contains an estimated 80,000 solar masses. The most remarkable feature of the cloud is its structure: it appears to have a central cavity, an elliptical disk-like body, and spiral arms. Chen’s team has suggested that the cloud owes its surprising structure to density wave theory — the same process thought to govern the formation of spiral arms in galaxies — but other possibilities such as collisions between molecular clouds can’t yet be ruled out. To learn more about the properties of this unusual molecular cloud, be sure to check out the full research article linked below.

Citation

“Discovery of a Giant Spiral Molecular Cloud in the Galactic Anticenter,” Xuepeng Chen et al 2026 AJ 172 4. doi:10.3847/1538-3881/ae6800

The post Featured Image: A Spiral Cloud in the Milky Way appeared first on AAS Nova.

Editor’s Note: This week we’re at the 248th AAS meeting in Pasadena, CA. Along with a team of authors from Astrobites, we will be writing updates on selected events at the meeting and posting each day. Follow along here or at astrobites.com for daily summaries, or follow @astrobites.bsky.social on Bluesky for more coverage. The usual posting schedule for AAS Nova will resume on 22 June

Table of Contents:

• Plenary Lecture: Ian Roederer, The Ultraviolet Path to the Origin of the Elements

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Plenary Lecture: Ian Roederer, The Ultraviolet Path to the Origin of the Elements (by Susanna Kohler)

When the universe first formed, the only elements present were the three lightest — hydrogen, helium, and lithium. Today, there are 118 confirmed chemical elements that make up the periodic table. So where did the heavier elements come from, when were they first created, and what can they tell us about the first stars that formed in the universe? In the final plenary of AAS 248, Ian Roederer (North Carolina State University) walked us through how ultraviolet observations are the key to understanding the origin of the elements.

We know that hydrogen, helium, and lithium were cycled through the earliest stars in the universe, where fusion and other processes produced the first heavy elements that were spit back out into the cosmos when these stars ended their lives as supernovae. According to Roederer, within just the first two or three generations of stars, every element with stable or long-lived isotopes had already been created. For the heaviest of these elements, the dominant source is likely a process called r-process nucleosynthesis, in which a rapid burst of neutrons bombards atomic nuclei, resulting in the quick capture of the neutrons to form very massive nuclei that subsequently decay to stable isotopes.

The conditions needed for r-process nucleosynthesis are too extreme to reproduce in a laboratory on Earth, so we rely on models and observations of the cosmos to better understand it. We know that to get a rapid burst of neutrons, you need some sort of explosive event — and, in fact, the first example of an r-process event caught in the act was GW170817, the first detected neutron star–neutron star merger.

But remember all those news headlines about how binary neutron star mergers produce gold and platinum? Roederer points out that these were all inferred results — we didn’t actually observe direct evidence of gold and platinum in the aftermath of this explosion. That’s because it’s very difficult to detect the spectroscopic emission lines of heavy elements. To do so effectively, Roederer argues, requires high-resolution ultraviolet (UV) spectroscopy. He showed that in a cool star, high-resolution UV spectra provide a 50% increase in the number of elements you can detect. The heaviest of elements are only detectable with spectra in the UV range.

Roederer walked us through some of the insights we can gain into the production of the heaviest nuclei found in nature when we use a combination of UV and optical spectroscopy. He also gave examples of what we can learn about even some of the lighter elements like phosphorus or boron when we have high-resolution UV spectroscopy to reveal the presence of these elements in low-metallicity stars.

Roederer ended his talk with a look ahead at the future of UV spectroscopy and the path to the universe’s first stars. Right now, the only mission we have that produces high-resolution UV spectroscopy is Hubble. NASA’s next big flagship mission with a high-resolution spectrograph, the Habitable Worlds Observatory (HWO), will be transformational in the ability to detect — or verify the absence of — heavy elements in stellar atmospheres. An observatory like HWO will provide our best shot at identifying low-mass, metal-free stars that survive from the first generation of stars in our universe. As Roederer concluded, “The future of studying the origin of the elements is bright in the UV.”

You can read Astrobites’s interview with Ian Roederer here.

The post AAS 248: Day 4 appeared first on AAS Nova.

Editor’s Note: This week we’re at the 248th AAS meeting in Pasadena, CA. Along with a team of authors from Astrobites, we will be writing updates on selected events at the meeting and posting each day. Follow along here or at astrobites.com for daily summaries, or follow @astrobites.bsky.social on Bluesky for more coverage. The usual posting schedule for AAS Nova will resume on 22 June.

Table of Contents:

• Plenary Lecture: Eliza Kempton, Common Worlds, Uncommon Complexity: Sub-Neptune and Super-Earth Atmospheres in the JWST Era
• Press Conference: Stars Reshaping Galaxies: Clusters, Feedback, and Explosive Aftermaths
• Plenary Lecture: George Helou, The Cosmic Infrared Window: Photons, Technology, and People
• Plenary Lecture: Carolyn Kuranz, Creating Astrophysical Conditions at High Energy Density Facilities
• Plenary Lecture: Cara Battersby, Our Galaxy’s Dynamic Center

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Plenary Lecture: Eliza Kempton, Common Worlds, Uncommon Complexity: Sub-Neptune and Super-Earth Atmospheres in the JWST Era (by Lexi Gault)

Eliza Kempton began her talk addressing the undergraduates in the room, showing the meeting website from AAS 200, which she attended as an undergraduate in 2002. Searching this page, there were no presentations on exoplanets — a stark difference from the boom of exoplanet science that we see 24 years later at AAS 248, marking how significantly a field can transform from the start of your career.

Situating us outside of the solar system, Kempton showed the quintessential mass–period plot of all 6,000+ detected exoplanets thus far. Strikingly, we have discovered new types of planets that are not seen in our own solar system, but uncovering exoplanet populations is heavily skewed due to detection limits. While it is much easier to find large planets closely orbiting their stars, occurrence rate studies have shown that small planets on close-in orbits are much more common and typically come in two sizes: gas-rich sub-Neptunes and rocky super-Earths. However, actually deciphering their compositions relies on detailed studies of their atmospheres, which is the primary research work Kempton dove into.

How do we study exoplanet atmospheres? Thankfully, JWST provides the wavelength range and collecting area necessary for observing the minute details in exoplanet atmospheres. Beginning with sub-Neptunes, Kempton laid out four important takeaways from recent work coming from her team:

1. Sub-Neptune atmospheres composed of heavier elements and molecules are common.
2. Clouds and hazes are pervasive for planets that get a moderate amount of light from their host star. Early JWST observations showed signatures that may point to soot formation in sub-Neptune inner atmospheres; this soot can rise, making the upper atmosphere we observe hazy.
3. Sub-Neptune atmospheres may provide a window into their interiors. Observed atmosphere compositions may indicate no solid planetary surface, but rather magma, water, and/or gas that can mix more readily with the upper atmosphere.
4. Tying atmospheric observations to formation scenarios is still a challenge. Constraints on planets’ bulk composition has not provided clear answers.

Moving down to super-Earths, Kempton introduced the idea of the cosmic shoreline — the empirical relationship between planetary escape velocity and stellar irradiation shows a stark dividing line between planets with and without atmospheres in our solar system. Does this concept of a cosmic shoreline exist for exoplanets? Kempton highlighted three takeaways for the study of super-Earth atmospheres:

1. Spectroscopy of super-Earth atmospheres presents degeneracies in determining their characteristics. A featureless spectrum could be due to the presence of heavy molecules and clouds, or it could just mean the planet has no atmosphere.
2. Thermal emission is a powerful tool for identifying candidate atmospheres. The eclipse depth of a transiting planet is directly related to the day-side temperature of the planet. Planets with and without atmospheres will have different day-side temperatures — hotter without an atmosphere, cooler with an atmosphere.
3. Many (but not all) transiting super-Earths are bare rocks. 

Clearly, JWST has allowed astronomers to make significant progress in understanding exoplanet composition and subsequently their possible formation and evolutionary histories. Kempton ended with reminding us where we came from 24 years ago — the field of exoplanet science has boomed, and we can wonder how much we’ll continue to uncover in the next 24 years.

Return to Table of Contents.

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Press Conference: Stars Reshaping Galaxies: Clusters, Feedback, and Explosive Aftermaths (Briefing video) (by Niloofar Sharei)

This press conference brought together four very different views of star-forming environments: the most distant galaxy cluster caught strongly lensing a background galaxy, the dense young star clusters tucked inside the rings of nearby galaxies, the extreme feedback physics inside the closest luminous infrared galaxy merger, and the first known pair of supernova remnants born from a binary star system.

A New Era of Galaxy Cluster Analysis at Cosmic Noon: JWST’s View of a Distant Galaxy Cluster

Kyle Finner (IPAC/Caltech), presented the discovery of strong gravitational lensing in XLSSC 122, the most distant known galaxy cluster, seen as it was about 10.3 billion years ago. When the team got their JWST imaging back, they noticed bright blue arcs around the brightest cluster galaxy, a clear signature of strong lensing from a background galaxy sitting in just the right place behind the cluster. Using those arcs, the team measured the radial dark matter profile and found that XLSSC 122 is much more centrally concentrated than cosmological simulations predict. To check whether the cluster itself is unusual, they combined the JWST result with multiwavelength data. All of those tracers show an elongated structure pointing the same way as the dark matter, which is a strong sign that XLSSC 122 is a merging cluster. But mergers usually lower concentration rather than boost it, so the question of why this early cluster looks so concentrated is still open. The team plans to follow up with more strong-lensing measurements. | Press release

Hidden Gems in the Hearts of Nearby Galaxies: Evolution of Young Massive Star Clusters in Circumnuclear Rings

Sajia Shahrin Neha (University of Kentucky) presented a study of young massive clusters in the circumnuclear rings of two nearby galaxies: NGC 3351, a normal spiral, and NGC 1097, which hosts an active galactic nucleus. Young massive clusters are extreme star-forming systems that pack hundreds of thousands to millions of stars into a small region, and the ring-shaped star-forming zones around these galactic nuclei provide exactly the kind of dense gas and dust reservoir these clusters need. Because the clusters are heavily obscured, optical, ultraviolet, and infrared light cannot pass through cleanly, so Neha and collaborators turned to radio continuum imaging with the Atacama Large Millimeter/submillimeter Array and the Very Large Array, which can see through the dust. Their team identified 53 young massive cluster sources across the two rings. They also placed them on an evolutionary sequence: heavily embedded “starless” clumps, newborn clusters that are just starting to become visible, and older “exposed” clusters that have already burned through much of their gas. All evolutionary stages are present in both galaxies, regardless of whether the host has an active nucleus. | NRAO press release | U. Kentucky press release

Dusty and Over-Pressured: Measuring Stellar Feedback in the Closest Luminous Infrared Galaxy

Deb/Debosmita Pathak (The Ohio State University/IPAC) presented new measurements of pre-supernova stellar feedback in NGC 3256, the closest luminous infrared galaxy and a merger between two roughly Milky Way–mass galaxies. NGC 3256 forms stars about 60 times faster than the Milky Way, which makes it a useful nearby laboratory for the intense, clumpy star formation that dominated the early universe. Using JWST plus multiwavelength data, the team measured feedback pressures around roughly 1,700 young star clusters and compared them with what we see in quieter, normal star-forming galaxies. The results break the standard picture in two ways. First, the feedback and interstellar medium pressures in NGC 3256 are about a hundred times higher than what is typical in normal star-forming galaxies. Second, the dominant feedback mode is different: instead of warm ionized gas pressure doing most of the work, ultraviolet and infrared radiation pressure on dust dominates in these much dustier environments. Even at these much higher pressures, most clusters are still over pressured relative to their surroundings, meaning radiation is strong enough to drive expansion against a dense ambient interstellar medium. | NRAO press release | OSU press release

Unveiling the First Binary-System Supernovae

Miltiadis Michailidis (Kavli Institute for Particle Astrophysics and Cosmology (KIPAC)/Stanford University/SLAC National Accelerator Laboratory) closed the session with the discovery of what appears to be the first known supernova remnant pair born from a binary star system. The starting point is IC 443, one of the best-studied supernova remnants and one of the brightest gamma-ray sources in the sky, thanks to its interaction with a dense nearby molecular cloud. Recent eROSITA observations showed that the faint X-ray “shell” long noticed next to IC 443 is in fact a second, overlapping supernova remnant. The question was whether the two are physically related or just a chance alignment on the sky. They used 15 years of Fermi gamma-ray data and modeled and subtracted IC 443’s contribution and uncovered a distinct, hidden gamma-ray source associated with the new remnant.

The gamma-ray emission is strongly spatially segregated: its northern boundary, where it overlaps the same molecular cloud that IC 443 illuminates, is dominated by accelerated protons colliding with dense gas, while its southern boundary is dominated by accelerated electrons. The team also showed that the optical filament along the northern boundary is a radiative shock that has cooled past the point of efficient particle acceleration. Combined with the fact that both remnants sit at the same distance (about 6,000 light-years), and that a population-synthesis run with a million massive binaries reproduces the observed separation and age difference, the team argues that the two remnants are the remains of a true binary pair. | Press release

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Plenary Lecture: George Helou, The Cosmic Infrared Window: Photons, Technology, and People (by Kerry Hensley)

George Helou (Caltech) gave a sweeping overview of infrared astronomy over the past 40 years, including the impressive role of the Infrared Analysis and Processing Center, or IPAC, which is celebrating its 40th anniversary.

The infrared portion of the electromagnetic spectrum is broad, encompassing wavelengths from 1 to 1,000 microns. In that wavelength range, there’s a lot going on in our universe: redshifted emission from distant galaxies, stars revealed by the drop in dust extinction, rotational and fine structure lines, molecular transitions, and fully half of the radiation density in the universe.

There have been many successful ground- and space-based infrared missions and surveys over the past four decades, starting with the Infrared Astronomical Satellite (IRAS), which proved the potential of infrared astronomy from space and set a new standard for making data accessible and well documented. Next, the Infrared Space Observatory (ISO) revealed the full span of infrared emission from objects like galaxies and gave researchers their first glimpse of H₂ lines. The Two Micron All Sky Survey (2MASS) produced the first fully digital survey of the sky at high angular resolution, creating a dataset that is still widely used. The Spitzer Space Telescope, the Wide-field Infrared Survey Explorer (WISE), the Herschel Space Observatory, and the Planck satellite followed, bringing a slew of new and unexpected discoveries, and pushing the field of infrared astronomy to longer wavelengths.

Helou introduced a few science areas in which infrared missions have contributed greatly. First was the study of polycyclic aromatic hydrocarbons (PAHs), which are a class of molecules containing interconnected rings of carbon atoms. Thanks to infrared instruments, astronomers showed that various unassigned spectral features arose due to PAHs and that these molecules were important for the heating and cooling of the interstellar medium. As infrared instruments became more capable, observations showed how the fraction of carbon that is locked up in PAHs changes with metallicity and revealed novel species like deuterated hydrocarbon nanoparticles.

In the field of exoplanets, IRAS found evidence of excess infrared emission around Vega, hinting at a disk of debris that was later confirmed. (IPAC was instrumental in this discovery; the star Vega was being used for calibration, and the calibration wouldn’t converge because of the unexpected infrared excess.) Later, ISO used spectroscopy to investigate stellar debris disks and showed that they were similar in properties to solar system comets. Though Spitzer wasn’t initially expected to be used for exoplanet studies, the telescope made the first detection of photons from the surface of a planet and helped to discover several planets in the TRAPPIST-1 system. (Here, IPAC played an integral role again; instrument teams and flight engineers worked to ready the spacecraft for exoplanet observations by modifying the heaters on the spacecraft for pointing stability and finding “sweet spots” for photometric stability.) Today, JWST continues to advance the field with sensitive measurements of exoplanet atmospheres.

Finally, Helou touched on the work that IPAC has done to archive data. IPAC maintains the NASA/IPAC Extragalactic Database, or NED, which receives at least three queries per second. It’s also responsible for the Infrared Science Archive, data from which is used in more than 50% of research articles. IPAC also manages the NASA Exoplanet Archive, showing that the center isn’t limited to infrared astronomy!

As for the future of IPAC and infrared astronomy, it’s clear that there is much left to explore and lots of exciting work to be done; the Roman Space Telescope is scheduled to launch in a few months, and within a few years the Near-Earth Object Surveyor will follow. The Ultraviolet Explorer, for which IPAC will provide the UVEX Science Data Center, is slated to launch in 2030, and the PRobe far-Infrared Mission for Astrophysics (PRIMA) is under final review.

Read Astrobites’s interview with George Helou.

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Plenary Lecture: Carolyn Kuranz, Creating Astrophysical Conditions at High Energy Density Facilities (by Lucas Brown)

While astronomy and astrophysics are often considered primarily observational sciences, with most targets of interest being millions to trillions of miles away from us — Carolyn Kuranz’s plenary talk helped to challenge this idea, demonstrating how we can sometimes bring the heavens down to Earth with high energy density (HED) facilities. The basic idea behind Kuranz’s work, and the field of HED laboratory astrophysics more broadly, is that some extreme astrophysical environments, particularly plasmas, can indeed be studied in the lab by producing smaller-scale analogs — so long as we choose the right types of experiments.

Kuranz structured her talk around three big questions she commonly gets asked about her field: firstly, why would astronomers want to do laboratory experiments? Then, what defines the “high energy density” in HED astrophysics? And finally, how do we actually do these experiments in practice? Starting with the why, Kuranz notes that studying systems in astrophysics is inherently difficult as a result of the fact that they are far away, and theoretical models can suffer from a lack of data or missing physics. Experiments can bridge the gap here, providing the ability to collect more data on specific systems of interest, complementing both theoretical models and observations.

While this philosophy can apply to a variety of laboratory astrophysics areas, such as laboratory-based studies of the chemistry of planetary atmospheres, Kuranz focused specifically on the emerging role of HED laboratory astrophysics. Typically, high energy density refers to systems with more than 1 million atmospheres of pressure and temperatures above 1 million K. Generally, this means we’re in plasma territory. In some ways, it’s only natural that studies of these sorts of environments would eventually help astrophysicists, given that around 99.9% of the matter in the universe is in plasma form. Despite this, the laboratory astrophysics side of HED physics has really only emerged over the past 30 years, with its origins being traced to work out of Lawrence Livermore National Lab, the current site of the National Ignition Facility (NIF).

Today, the NIF is only one of a few dozen facilities in which HED laboratory astrophysics experiments are conducted. This is because the type of equipment needed to reproduce environments analogous to various astrophysical systems can vary greatly. This gets to Kuranz’s third question of how these experiments are conducted. The process begins by answering a set of questions, including: do the astrophysical and proposed laboratory environments obey the same governing equations (conservation of mass, momentum, etc.)? Is one able to re-scale the physical parameters in each system (timescale, size, density, pressure, etc.) in a way that retains relevant dynamics like viscosity, Reynolds number, and so on? Once these details have been nailed down, a researcher can assess what types of facilities they may need. For example, the NIF, which uses symmetrical arrangements of lasers to compress and heat up millimeter-scale pellets containing gases that can undergo nuclear fusion, provides a fairly natural environment for studying processes in the cores of stars, which are also hot, dense, and neutron-rich environments where fusion is actively occurring.

As for the future, things look promising for HED laboratory astrophysics — since the NIF achieved “ignition” in 2022, producing a net gain of energy from one of these pellet-crushings for the first time, a huge amount of interest and investment has been flowing into facilities studying HED physics. These facilities range from private companies working to achieve sustained nuclear fusion power generation to longstanding federal research centers working on understanding nuclear weapons and stockpile management, but they all provide astronomers with the opportunity to do what was once unthinkable: bring the universe’s most extreme environments down to Earth.

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Plenary Lecture: Cara Battersby, Our Galaxy’s Dynamic Center (by Niloofar Sharei)

Cara Battersby (University of Connecticut) used her plenary to walk us through her group’s ongoing effort to understand one of the most extreme environments in our own galaxy: the central molecular zone (CMZ), which is a dense, turbulent gas reservoir at the heart of the Milky Way. Her talk pulled together large surveys, new high-resolution zoom simulations, and machine-learning methods designed to bridge between the two.

She opened with the PRobe far-Infrared Mission for Astrophysics (PRIMA), the far-infrared probe mission concept she is a co-investigator on. This mission concept was developed in response to NASA’s recent billion-dollar probe mission call, and selection is expected later this year. PRIMA covers roughly 1.8–25 microns with imaging and spectroscopy, and galactic ecosystems make up about a quarter of its science case.

Battersby paused mid-talk to speak directly to early-career people in the audience about work-life balance, including bringing her daughter and sister with her to the meeting, and the SPARK program at UConn that supports women and underrepresented groups in physics. Her message: astronomy should be done from a place of joy, and visible work-life balance is something the community should be more open about.

Battersby framed the Milky Way as the natural laboratory for star formation across a huge range of environments, and briefly reviewed the ALMAGAL survey, which observed roughly 1,000 high-mass star-forming regions across the disk. But her main focus was the CMZ, which she argued is essentially a different kind of galaxy embedded inside our own. About 80% of all the dense molecular gas in the Milky Way sits in the CMZ, and its gas properties — density, turbulence, temperature, and pressure — are extreme compared to the rest of the disk. Because nearby starburst and high-redshift environments share many of these properties, the CMZ is the closest place we can actually resolve individual star-forming cores under conditions that resemble the early universe.

She showed that gas in the CMZ is extremely filamentary across all scales, and that the relationship between dense gas and star formation rate is unusual: when individual clouds in the CMZ actually form stars, they form them much like clouds elsewhere in the galaxy, but a large fraction of the dense gas in the CMZ never engages in star formation at all. Battersby argued that this is likely because so much of that gas is being shaped by flows toward the black hole and the strong turbulence and dynamics of the central environment, and it never cools and collapses into stars.

She closed with the simulation and machine-learning side of the program. Her group runs zoom simulations that can follow individual star-forming regions and can resolve down to CMZ scales while still capturing the full ~5 kpc bar driving gas inward. To extract more from these simulations than just side-by-side image comparisons, the team built a GPU-accelerated radiative transfer code that runs roughly 10,000 times faster than existing codes. They generate hundreds of thousands of synthetic observations and use them to train an encoder–decoder convolutional neural network that learns to predict the top-down structure of a region from the side-on view we actually observe. Applied to the CMZ, the network produces 3D reconstructions that are physically plausible and broadly consistent across independent training runs.

Read Astrobites’s interview with Cara Battersby.

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The post AAS 248: Day 3 appeared first on AAS Nova.

Editor’s Note: This week we’re at the 248th AAS meeting in Pasadena, CA. Along with a team of authors from Astrobites, we will be writing updates on selected events at the meeting and posting each day. Follow along here or at astrobites.com for daily summaries, or follow @astrobites.bsky.social on Bluesky for more coverage. The usual posting schedule for AAS Nova will resume on 22 June.

Table of Contents:

• Helen B. Warner Prize Lecture: Kyle Kremer, Globular Clusters: Astronomical Factories of Gravitational-wave and Electromagnetic Transients
• Press Conference: Our Changing Galaxy and the Skies We See
• High Energy Astrophysics Division Early Career Prize Lecture: Carolyn Kierans, Developing Next-Generation MeV Telescopes
• Press Conference: Fire and Ice in Planetary Systems Near and Far
• Solar Physics Division George Ellery Hale Prize Lecture: Yi-Ming Wang, The Sun as a Laboratory for Astrophysical Magnetic Fields
• Plenary Lecture: David Jewitt, The Interstellar Interlopers

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Helen B. Warner Prize Lecture: Kyle Kremer, Globular Clusters: Astronomical Factories of Gravitational-Wave and Electromagnetic Transients (by Lucas Brown)

Kyler Kremer (University of California, San Diego) kicked off day two of AAS 248 with a “dynamic” talk on the complex interactions and environments that exist within globular clusters — the most massive category of stellar clusters, which can contain upwards of one billion stars. Because of the extreme stellar density of these environments, they are thought to be good factories of systems ranging from accreting white dwarfs to millisecond pulsars, which are often spun up to high speeds via accretion from companion stars. Such accretion, whether onto pulsars or other compact objects, can often generate bright X-rays, and as Kremer noted early on in his talk, it was in fact these X-ray sources that provided some of the earliest evidence of the abundance of exotic systems within globular clusters. By the early 2000s, hundreds of X-ray sources had been identified in globular clusters.

Along with these brightly emitting compact binary systems, we expect globular clusters to be home to a vast population of darker, more elusive objects — black holes. Kremer noted that because about one out of every thousand stars is thought to be massive enough to evolve into a black hole, older globular clusters are thought to produce tens or hundreds of thousands of black holes over time. These black holes are then expected to gradually sink towards the centers of the clusters through dynamical friction, where they will increasingly find themselves in the company of other black holes, or black hole binaries. As these massive objects swing by each other, they can occasionally merge or eject black holes out of clusters entirely. This leads to a complex evolutionary history, leaving many open questions in regards to how many black holes should persist in globular clusters today and with what properties.

Luckily, strong evidence for the presence of black holes in globular clusters began to come in around the early 2000s as a result of the direct measurements of stellar orbits around an invisible, at least 4-solar-mass object in NGC 3201. Since this discovery, multiple others have been made via similar techniques. The role of black holes in shaping our observation of globular clusters may go well beyond these isolated systems, however. Theoretical work has also shown that the presence of black hole binaries in the centers of globular clusters may contribute to dynamical heating of the overall cluster. This suggests that globular clusters that have not undergone core collapse, which represents over 80% of clusters, should retain significant black hole populations today.

While individual black holes can often be hard to spot, black hole binaries are becoming increasingly easy to hear, thanks to the advent of gravitational wave astronomy. At facilities like LIGO, Virgo, and KAGRA, merging black hole binaries are now regularly detected, creating a population-level catalog of black hole binary properties. While many of these systems can be well explained by black holes formed in the “isolated” channel, meaning originating from a preexisting binary star system, some mergers show signs of a “dynamical” formation history, which can arise in the sort of dense environments globular clusters provide. As one example, there seems to be more black holes in the 40-solar-mass and above range than many models predicted. At these high masses, more potential progenitor stars actually become too large to form black holes thanks to a phenomenon called pair instability. However, such massive black holes could be formed from the repeated mergers of smaller black holes — a hierarchical process that simulations have consistently shown can be highly efficient in globular clusters, especially the most massive ones. On top of this, Kremer noted that individual gravitational wave signals have recently shown other telltale signs of hierarchically formed binary black holes, such as asymmetric masses and spin–orbit misalignment.

Finally, Kremer turned to another class of exotic astrophysical objects to explore other ways globular clusters can generate interesting phenomena: pulsars. Pulsars, like black holes, form from the collapse of massive stars. This rapidly rotating sub-category of neutron stars beams radiation from their poles, which gradually slows them down and depletes the strength of their radio emission over millions or billions of years. Because of this, one would expect older globular clusters to have a slowly rotating and mostly invisible population of pulsars. Instead, we see many rapidly rotating millisecond pulsars in these environments, suggesting that the dense cluster environment allows for many of these systems to be spun back up through accretion from other stars. In contrast, we also see young globular clusters which contain slowly rotating pulsars — another puzzle, yet one that may again be explained by the dense environment. Some researchers believe that these pulsars are formed via the direct merger of multiple white dwarfs, rather than from the collapse of a massive star. Such systems may also be the source of some fast radio bursts; the first fast radio burst associated with a globular cluster was discovered in 2020. It seems like globular clusters may be the gift that just keeps on giving!

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Press Conference: Our Changing Galaxy and the Skies We See (Briefing video) (by Niloofar Sharei)

This press conference walked through four very different ways our view of the Milky Way and our skies are changing right now — from extreme gas physics at the Galactic Center, to the hidden stellar populations of a cluster, to the rapid flickers of dying stars, and finally, to a very practical question: what are dark night skies actually worth to the public?

Resolving the Supersonic-to-Subsonic Gas Transition in the Galactic Center for the First Time

Rojita Buddhacharya (Center for Astrophysics | Harvard & Smithsonian; Liverpool John Moores University) presented new results from the central molecular zone (CMZ), the dense gas reservoir at the center of our galaxy about 25,000 light-years from Earth. The CMZ is one of the most extreme environments we know of: gas there is roughly a hundred times denser, hotter, and more turbulent than what we see in nearby molecular clouds. Despite holding huge amounts of star-forming fuel, the CMZ forms stars at a surprisingly inefficient rate, and one of the puzzles is what conditions actually let any of that gas collapse into stars.

Buddhacharya mapped how gas transitions from highly turbulent, supersonic motion to calmer, subsonic motion across a region in the CMZ. This transition is well known in nearby clouds, where it usually precedes gravitational collapse, but it had never been clearly resolved in the CMZ before. Their team found a “calm island” of subsonic gas embedded in the otherwise turbulent sea. This is the first observation of its kind in the galactic center.

The Multi-Age Stellar Populations of Terzan 5 as Revealed by JWST

R. Michael Rich (University of California, Los Angeles) presented new JWST and Hubble Space Telescope observations of Terzan 5, an unusual stellar system near the center of the Milky Way that looks like a globular cluster but doesn’t act like one. Earlier work had already shown that Terzan 5 hosts at least two distinct stellar populations with very different ages and chemical abundances, which is unusual for a typical globular cluster.

Because Terzan 5 sits behind a thick screen of foreground stars and dust, separating real cluster members from contamination is one of the hardest parts of the analysis. The team combined JWST and Hubble imaging to measure stellar proper motions, then used a vector point diagram to isolate the stars that move together with the cluster. They identified two additional stellar populations beyond the two already known. Rich argued that Terzan 5 may be a “fossil fragment,” possibly the leftover core of a small galaxy or early bulge structure that was accreted long ago.

Sub-Day Periodic Variability of Two Central Stars of Planetary Nebulae

Gaoyang Du (Dalian University of Technology) reported the discovery of new short-period signals in the central stars of two planetary nebulae. These central stars are the hot, exposed cores left behind by Sun-like stars at the end of their lives, and finding rapid brightness variations in them tells us about their interior structure and pulsation physics.

Short-period signals well under a day are very hard to recover from the ground because Earth’s rotation introduces strong one-day aliasing, so the team turned to the Transiting Exoplanet Survey Satellite, which observes continuously from space. Using a neural-network pipeline designed to handle the crowded, contaminated backgrounds these stars sit in, they recovered the previously known variability in NGC 1501 and detected a new signal at roughly half an hour. Follow-up spectroscopy will be needed to pin down whether the signals come from pulsations, rotation, or something else, but the result opens a new window on the rapid variability of dying-star cores.

Artificial Light at Night Significantly Degrades the Value of Public Lands

Jordan Smith (Utah State University) closed the press conference with a very different kind of measurement: the economic value of dark night skies. While astronomers usually treat light pollution as an observing problem, Smith and his collaborators are asking what the public is actually losing and what people would pay to keep dark skies on public lands. The team surveyed 634 visitors across International Dark Sky-certified parks, asking detailed questions about visitation behavior, motivations, and willingness to pay. Combining those surveys with satellite-based sky-brightness data, they estimated how the actual darkness of a site translates into the value visitors place on a trip. Based on the survey results, they found that visitors were willing to pay $45 more per visit to go to a park with skies one level darker on the Bortle scale. That sounds small per visitor, but scaled across all visits to all dark-sky public lands, it represents a very large economic value tied to a public good that current policy frameworks rarely account for.

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High Energy Astrophysics Division Early Career Prize Lecture: Carolyn Kierans, Developing Next-Generation MeV Telescopes (by Niloofar Sharei)

Carolyn Kierans (NASA Goddard Space Flight Center) was awarded the AAS High Energy Astrophysics Division Early Career Prize for her work on developing the next generation of megaelectronvolt (MeV) gamma-ray telescopes. Her talk laid out why the MeV band is so valuable (it contains nuclear emission lines like the 511 keV positron-annihilation line that traces high-energy processes in our galaxy) and why it has been so technologically difficult to observe well, since photons at these energies do not focus easily and the dominant interaction in the detector is Compton scattering. She walked through her work using balloon-borne Compton telescopes to mature the technology, the tools her team has developed in recent years to improve event reconstruction, and the broader roadmap for the next generation of MeV instruments.

Read Astrobites’s interview with Carolyn Kierans.

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Press Conference: Fire and Ice in Planetary Systems Near and Far (Briefing video) (by Kerry Hensley)

The afternoon press conference was convened by Astrobites’s own Niloofar Sharei, this meeting’s Astrobites Media Intern. First up in the parade of planetary presentations was Neal Turner (NASA’s Jet Propulsion Laboratory/Caltech). Turner’s focus was Io, a moon of Jupiter and the most volcanically active body in the solar system. Turner’s team put forward a new claim: that the long-lived volcanoes that speckle Io’s surface spew out volcanic ash in their plumes, producing enough of this material to rapidly erase impact craters.

The team modeled Io’s plumes in order to explain the moon’s lack of impact craters, understand how certain plumes have persisted on Io for more than 45 years, and motivate a possible mission concept that includes a plume flythrough and sample return. They modeled the formation of ash as magma rises in a volcanic vent as well as the trajectory of the ash once it’s ejected into the plume, aiming to 1) match the plume observations from the Galileo spacecraft and 2) understand how an ash-filled plume might look different from one filled only with sulfur dioxide. While Turner found that Galileo data couldn’t discern between the two scenarios, ash makes a dramatic difference at the sub-millimeter wavelengths accessible to the Atacama Large Millimeter/submillimeter Array, which the team hopes to use to test this prediction. Finally, returning to the development of the mission concept, Turner proposed using a probe to first fly through the shadow of a plume to assess the particle size before sending the spacecraft through to collect a sample.

Up next, Tunhui Xie (University of California, Los Angeles) turned to Io’s neighbor, Europa. Europa and the other large icy moons of Jupiter are of interest to researchers because they might have subsurface oceans. Observations of Europa from ~30 years ago show that the moon has strange radar properties: its radar albedo is large, and the return signal retains the strong circular polarization of the outgoing signal.

To investigate the moon’s radar weirdness further, Xie’s team observed Europa from 2011 to 2024 and showed that the moon’s albedo (fraction of light reflected from its surface) is roughly constant with longitude. There is some evidence of differences between Europa’s hemispheres, which could be a sign of spiky ice structures called penitentes protruding from the frosty surface; Europa’s trailing hemisphere might be subjected to more particles from Jupiter’s magnetosphere, which could suppress the growth of penitentes in that region and cause a difference in the albedo. Xie also addressed the polarization behavior of the radar signal, showing that this is likely due to the coherent backscatter opposition effect. Finally, Xie showed how observations helped to place an upper bound of 32 meters for the penetration depth of X-band radar photons into Europa’s icy shell.

Bryce Bolin (Eureka Scientific) reported on the third known visitor from another star system: 3I/ATLAS. Using the Multi-Object Spectrograph for Infrared Exploration on the Keck I telescope, Bolin’s team obtained some of the first infrared images of the interstellar visitor and detected its fuzzy coma — the cloud of gas and dust that surrounds the solid body of the comet — shortly after its discovery in July 2025. In August, observations revealed that the comet had started to grow a tail. As the team monitored 3I/ATLAS during its journey through our solar system, they saw significant changes. The comet was initially very red, likely due to space weathering from the galactic environment, but it became greener as the comet became active and refreshed its surface.

In some of the earliest spectroscopy taken by a large-aperture telescope, Bolin’s team found cometary volatiles like CN, but not C₂ or C₃, which are common in comets, giving them a green color. These missing species emerged a couple of months later, which coincided with the comet taking on a greener appearance. As the comet retreated from its encounter with the Sun, these emission features faded. This presentation by Bolin showed how early and continuing monitoring of an interstellar object by a large-aperture telescope can reveal how these objects are affected by their journeys through our solar system.

Moving out of the solar system entirely, Tiffany Kataria (NASA JPL/Caltech) turned the discussion toward exoplanets. Kataria discussed HD 80606b, a 4.1-Jupiter-mass planet on an extremely eccentric (e = 0.93) orbit with a period of 111 days around a solar-type star. Kataria used JWST to observe HD 80606b’s phase curve, which revealed different parts of the planet as it travels along its orbit. Each time the planet makes its extremely close approach to its host star, it gets “flash roasted” and experiences a rapid increase in temperature. This rapid heating event is complex, depending on factors like the planet’s atmospheric chemistry and winds. The JWST data revealed that HD 80606b’s temperature skyrockets an incredible 1,100℉ over the course of its orbit. There’s still much more to learn from the rich spectroscopic dataset from JWST, so keep an eye out for more findings about this flash-roasted exoplanet in the future!

Finally, Aurora Kesseli (IPAC/Caltech) discussed another toasty exoplanet called CoRoT-2b, which is a hot Jupiter on a 1.7-day orbit around its star. Because hot Jupiters orbit their hosts so closely, astronomers expect all of these extreme exoplanets to be tidally locked, with one side of the planet perpetually facing the star and the other side in perpetual darkness. However, CoRoT-2b might be breaking that trend. In 2018, researchers reported that CoRoT-2b had winds that blew in the opposite direction from all other known hot Jupiters. They drew this conclusion from the location of the hottest point on CoRoT-2b, which appeared just after the planet ducked behind its star, rather than just before — unlike all other hot Jupiters studied so far. At the time, researchers hypothesized that the unusual location of the hotspot was due to clouds on one side of the planet, a magnetically induced westward wind, or a lack of tidal locking.

Using new data from the Very Large Telescope and Gemini South, Kesseli found that the planet’s strange properties can be explained best by a lack of tidal locking. CoRoT-2b appears to rotate at 2.24 km/s — far slower than the 4.37 km/s expected if the planet were tidally locked. There are no theories yet that explain why CoRoT-2b wouldn’t be tidally locked, so it remains a mystery for now!

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Solar Physics Division George Ellery Hale Prize Lecture: Yi-Ming Wang, The Sun as a Laboratory for Astrophysical Magnetic Fields (by Kerry Hensley)

Yi-Ming Wang (Naval Research Laboratory) gave the AAS Solar Physics Division’s George Ellery Hale Prize Lecture for “sustained, foundational contributions to understanding solar magnetism, the solar cycle, and the solar wind.” Wang is perhaps most known for the Wang–Sheeley–Arge solar wind model, which is widely used in space weather forecasting.

Wang began by musing on how his winding career path brought him to solar physics. Initially a theorist who modeled neutron stars, Wang was later hired to do radio astronomy but arrived for the position later than expected, so he was roped into working on solar physics instead — where he learned many things about magnetic fields that he wished he’d known when working on neutron stars!

In this talk, Wang gave an overview of three aspects of the Sun related to its magnetic field: quasi-rigid rotation of coronal holes, the source of coronal heating, and the speed of the solar wind. First up, coronal holes: these are dark areas in the solar corona where magnetic field lines stream out into space, which solar physicists call “open” field lines. (“Closed” field lines curve back to the solar surface.) Wang described how we know that coronal holes are regions of open field lines by extrapolating the photospheric magnetic field. (The photosphere is the visible “surface” of the Sun.) Because coronal holes rotate quasi-rigidly (compared to the photosphere, which rotates differentially), magnetic field lines must be continually converted from closed to open and vice versa at the boundaries of these holes.

Next, Wang discussed the source of coronal heating. The solar corona is famously extremely hot, running at a few million degrees compared to the ~6000K solar photosphere. For decades, the Parker nanoflare model has been the leading explanation for how the corona gets so hot. In this model, the places where coronal loops touch down in the solar photosphere are continually wiggled around by random motions of the photosphere, which tangles up the magnetic field lines in the coronal loop. When the current sheets in this system dissipate, the corona is heated. Instead, Wang favors an observationally based model in which the heating comes from magnetic reconnection with underlying small-scale fields.

Finally, Wang briefly touched on the connection between the Sun’s magnetic field and the speed of the solar wind. The solar wind has been measured at Earth since the 1960s, and these measurements have shown that the mass and energy flux density of the solar wind scales with the strength of the footprint magnetic field strength, but the observed solar wind speed is independent of the footprint field strength. Instead, the speed scales inversely with the rate of magnetic flux-tube expansion in the corona. Thus, the solar wind speed at Earth can be calculated from the rate of flux-tube expansion along open magnetic field lines using maps of the photospheric magnetic field.

In the end, Wang’s work on the solar magnetic field did connect back to his earlier work in high-energy astrophysics, with relevance to period changes in binary pulsar systems and other areas. Magnetic fields really do connect all parts of astrophysics!

Read Astrobites’s interview with Yi-Ming Wang.

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Plenary Lecture: David Jewitt, The Interstellar Interlopers (by Niloofar Sharei)

David Jewitt focused his plenary talk on a rare kind of small body: the three confirmed interstellar objects that have passed through the solar system so far. He opened with the Oort cloud as a framing device. Comets in the Oort cloud did not form there — they formed near the giant planets and were scattered out by gravitational interactions. The same process leaks comets to interstellar space very efficiently: only about 1–10% are trapped into a star’s own Oort cloud. Across the galaxy, that implies a free-floating population on the order of 10²⁴–10²⁵ objects. Seeing some of them pass through our solar system is exactly what we should expect.

The bulk of the talk walked through the three known interlopers. ʻOumuamua (1I/2017 U1) is the strangest: a tiny inert body about 80 meters across, with an extreme light curve consistent with either a 6:1 elongated shape or a flattened disk, and a non-gravitational acceleration of about 0.1% of solar gravity despite no detectable outgassing. Jewitt walked through the proposed explanations: exotic ices, ultra-low-density fluffballs, and sail-like sheets, and showed why each runs into a physical problem. 2I/Borisov (2019), by contrast, looks like a perfectly normal comet, with a ~400–500-meter nucleus, a coma, a tail, and a solar-system-like composition. 3I/ATLAS is the largest at roughly a kilometer, and JWST infrared spectroscopy has revealed CO₂ emission about an order of magnitude richer than typical solar system comets. This is the first detailed look at the volatile inventory of an interstellar visitor.

Jewitt then turned to what the three objects tell us as a population. The strongest constraint comes from ʻOumuamua, precisely because its discovery was such a near miss: catching one in that brief visibility window implies roughly 1,000 similar objects crossing the solar system per year. The three objects look very different in size, activity, and composition, which is consistent with sampling a broad galactic population, and their velocity dispersion lines up with the disk-heating picture, in which older galactic populations are kinematically hotter. The leading origin story is the same one he set up at the start: scattering from the protoplanetary disks of giant planets around other stars.

Read Astrobites’s interview with David Jewitt.

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The post AAS 248: Day 2 appeared first on AAS Nova.

Editor’s Note: This week we’re at the 248th AAS meeting in Pasadena, CA. Along with a team of authors from Astrobites, we will be writing updates on selected events at the meeting and posting each day. Follow along here or at astrobites.com for daily summaries, or follow @astrobites.bsky.social on Bluesky for more coverage. The usual posting schedule for AAS Nova will resume on 22 June.

Table of Contents:

• Fred Kavli Plenary Lecture: Richard Teague, Revealing the Dynamics of Planet Formation
• Press Conference: The Science of Stellar Remnants
• Plenary Lecture: Sanmi (Oluwasanmi) Koyejo, The Measurement Gap: What AI Can Get Wrong and Why Astronomers Are the Fix
• Press Conference: Variable, Windy, and Disruptive: The Behavior of Supermassive Black Holes
• Plenary Lecture: Mario Juric, Early Results from the Rubin Observatory: Mapping the Solar System and Beyond
• Plenary Lecture: Esra Bulbul, Cosmology and Baryons Across Scales: Probing Halo Mass Function to Cosmic Filaments with eROSITA

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Fred Kavli Plenary Lecture: Richard Teague, Revealing the Dynamics of Planet Formation (by Lexi Gault)

Richard Teague (Massachusetts Institute of Technology) gave the Fred Kavli Plenary Lecture on his groundbreaking work in the dynamics of planet formation. The study of planet formation, as Teague introduced, has advanced significantly in the last two decades with the discovery of thousands of exoplanets and the launch of cutting-edge instruments. While planets are found everywhere orbiting a wide variety of stars, not all planetary systems look the same. Our solar system looks very different from other exoplanetary systems, challenging our understanding of planet formation and requiring us to build a picture that works across the board.

Where do we look to build a better understanding of planet formation? Planets are inherently the byproduct of star formation, forming in protoplanetary disks around new stars. These disks are filled with gas and dust, concentrating mass into rings that then eventually form planets. Exactly how this process proceeds is variable, and the resulting planetary system depends on how the material in the protoplanetary disk mixes and combines into planets. Teague compared planets to bread: we know the simple list of ingredients that it takes to make them, but what you end up with depends on how you bring those same ingredients together. We need to study what is happening in the planetary mixing bowls to understand how planets form.

Leveraging the high spatial and spectral resolution of the Atacama Large Millimeter/submillimeter Array (ALMA), Teague and collaborators have developed exoALMA, a planet-hunting campaign focusing on the still-forming planets of protoplanetary disks. This project has focused on 15 sources, obtaining and analyzing high-resolution observations to explore the kinematics, 3D velocity structures, and mass distributions within these protoplanetary disks.

The first science results from exoALMA have started to reveal that the planet formation process is highly dynamical — precise kinematic measurements uncover dynamical perturbations within protoplanetary disks across their sample. These perturbations point to the impacts protoplanets have on disk kinematics and mass distributions as they continue to form, and the high resolution of ALMA observations unlocks the inner workings of protoplanetary disks.

Looking forward, Teague emphasized that the future is broad for planet formation science. The upcoming Wideband Sensitivity Upgrade on ALMA will enable even more detailed maps of protoplanetary disks, unlocking the mysteries of planet formation while it happens.

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Press Conference: The Science of Stellar Remnants (Briefing video) (by Lucas Brown)

In AAS 248’s very first press conference session, we heard from a variety of scientists and research teams on all sorts of stellar remnants: white dwarfs, supernovae, pulsars, and beyond. Basically, if it came from a dying star, it was fair game for this session.

Boron and Beryllium as Unlikely Probes of Extrasolar Planets

First up was Ben Zuckerman (University of California, Los Angeles), who updated us on ongoing research into the presence of boron and beryllium in certain white dwarf systems. For some context, there exist many white dwarf systems in which a companion object — sometimes a planet — can have its material accreted onto the surface of the white dwarf due to tidal disruption during close approaches in its orbit. This deposition of material can then be detected via spectral signatures in observations of the white dwarf.

In 2021, evidence was first presented for two white dwarfs being “polluted” with trace amounts of beryllium, which is a particularly rare element, cosmically speaking. This raises the question of how so much beryllium ended up in these systems. In the hunt for answers, however, another mystery has emerged: missing boron. As Zuckerman went on to describe, boron was also recently discovered in some of these white dwarf systems, but at an abundance roughly equal to that of the beryllium. This is despite boron being about a hundred times more common in the universe, further muddying the waters of what exactly is causing such a strange pattern of heavy metals in these systems. Work remains ongoing to find a physical model that can reconcile these observations.

White Dwarf Kicks via Episodic Mass Ejection from Red Giant Stars

Next we heard from Jim Fuller (Caltech). Fuller filled us in on some recent studies aiming to explain why white dwarfs often obtain such high velocities when formed. Just like our own Sun occasionally ejects plumes of plasma from its surface, the red giant stars that eventually form white dwarfs are expected to periodically undergo mass-ejection events. But unlike with our own Sun, these ejections can shear off a significant amount of the star’s total mass — up to ~0.01% per ejection. Each time such an ejection occurs, Newton’s 3rd law ensures that the star itself will also receive a random velocity boost in the opposite direction. Over many thousands of ejections, assuming they occur randomly in all directions, this can significantly “kick” a meandering red giant up to speeds exceeding half a kilometer per second. Once such a star collapses to form a remnant white dwarf, the white dwarf will have this excess velocity too.

Additionally, this random ejection process predicts that red giants in binary systems will experience a sort of “random walk” in their orbital parameters, not just their overall velocity. This can lead to the complete dissociation of binaries, or to the direct collision of a red giant with its companion — leading to predictions about how many widely spaced white dwarf binary systems should exist. | Press release

Probing Intrabinary Material in a New Spider Millisecond Pulsar

Rebecca Kyer (Michigan State University) gave an update on research into so-called “spider” millisecond pulsars. These rapidly rotating neutron stars are a sub-class of pulsar characterized by their very high spin rate and the presence of a companion from which the pulsar is accreting material. Such systems are further sub-classified as either “Black Widows,” which have very low-mass companions (~3% solar mass), “Redbacks,” which have larger companions at ~10-80% solar mass, and “Huntsmans,” which have more massive red-giant companions. These Huntsman pulsars are the newest category, with only two known cases — until now!

Kyer presented evidence collected by their team that may indicate the discovery of a third Huntsman pulsar. The evidence involves radial velocity measurements of the companion star, which shows an orbital period of 3.64 days and variable H-alpha emission. In these systems, the radio emission typically associated with the pulsar can be blocked from our view for unpredictable amounts of time due to clouds of hot gas and dust that emerges from the complex interaction between the pulsar and red giant winds. Despite this, Kyer hopes that with enough targeted observations with the Green Bank Telescope, a radio signal will eventually be detected, confirming the pulsar’s presence.

NASA’s Chandra Finds Unexpected Fireworks in Aftermath of Stellar Explosions

Finally, we heard from a team of three researchers — Andrea Prestwich (Catholic University of America / NASA Goddard SFC), Roy Kilgard (Wesleyan University), and Zoe Hoiland (Vassar College) — on an unexpected supernova discovery. Traditionally, supernovae are modeled as having a relatively constant or slightly decreasing luminosity, at least after their initial explosion. As the stellar material is blasted away from the progenitor’s core, it interacts with the surrounding interstellar medium and a blob of hot, shocked gas is left over. This blob will eventually cool and dim, but often over a long time period, leading to the aforementioned prediction of constant or slightly decreasing brightness.

However, in 14-year Chandra observations of a supernova remnant in Messier 83, Prestwich and her collaborators actually found significant X-ray variability, with the remnant occasionally even increasing in brightness. In a follow-up study, it was found that supernova remnants in Messier 51 likewise show this up-and-down variability. In contrast, an analysis of remnants in Messier 101 showed zero variable remnants. Notably, the former two galaxies are very actively star-forming, while the latter is not. Some possible theoretical models to explain this variability include the possibility of stellar material falling back on the compact object leftover by the supernova, creating an accretion disk that can generate variable emission. Alternatively, it has been proposed that there could be a neighboring star to the remnant object, forming an accreting X-ray binary system that could also induce variability. | Press release

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Plenary Lecture: Sanmi (Oluwasanmi) Koyejo, The Measurement Gap: What AI Can Get Wrong and Why Astronomers Are the Fix (by Lexi Gault)

Sanmi (Oluwasanmi) Koyejo, a professor of computer science at Stanford University, focused this plenary talk on the limitations of AI as it becomes more integrated with science and how astronomers can help solve these problems. Koyejo began by addressing the question of why an AI researcher is talking to astronomers. His research explores how to set AI standards and how to best assess the performance of an AI model, which becomes particularly important when these models are used to do science.

Evaluating the performance of an AI model relies on benchmarks, a fixed set of questions with known answers that are used to score the AI. These benchmarks are simple, reproducible, and comparable, but passing a benchmark does not equate to getting a meaningful scientific result. Benchmarks assume cheap checks, fast feedback, and fixed questions, but science is none of those things; answering astronomy questions relies on telescope time, and ground truth cannot be found quickly.

Much like telescopes, AI benchmarks are measuring instruments with noise that can compound. If you run an AI model many times, the goal is often convergence on an agreed-upon answer, but getting to an agreed-upon answer does not mean that the answer is correct. Koyejo’s recent research found that AI models more often agreed with each other than they did with the actual truth. This is made worse when AI is used to evaluate itself. For example, Koyejo notes the rising number of academic paper submissions due to AI-written papers greatly exceeds the capacity of human reviewers. If AI tools are used to evaluate AI-generated paper submissions, the AI will tend to favor AI-written materials, ignoring the actual scientific merit. Making evaluation of AI an AI problem compounds its failures, straying further from a correct answer.

This is where astronomers come in. Having the expert knowledge of what “correct” looks like, being able to judge which errors matter, access to expensive ground truth (telescope time), and a culture of blind analysis (not knowing exactly what the answer should be), astronomers are well equipped to build standards for AI evaluation. We can define what good AI is for astronomy and use our expertise to help build the standards. Koyejo left the audience with the charge to engage with AI (engagement does not mean endorsement), so that astronomers can help set the standards for appropriate AI use in science.

Read Astrobites’s interview with Sanmi Koyejo.

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Press Conference: Variable, Windy, and Disruptive: The Behavior of Supermassive Black Holes (Briefing video) (by Niloofar Sharei)

This press conference focused on what supermassive black holes do to the world around them, from relativistic jets of the most famous black hole, to the multi-phase winds launched from active galactic nuclei, to temperature-shifting coronae, and even the radio burps that are produced years after a black hole tears apart stars.

Chandra Tracks the Evolving Jet from Messier 87’s Black Hole: 

Camille Poitras (Laval University) presented the largest Chandra X-ray movie of jet evolution in the famous supermassive black hole Messier 87 (M87). M87 has been studied across the electromagnetic spectrum, but X-ray observations of its jet have always suffered from blur because high-energy photons are hard to focus. Using improved Chandra calibrations and deconvolution techniques, the team produced a 13-year X-ray movie of M87’s jet from 2012 to 2025. Tracking a bright knot within the jet, Poitras’s team saw it split into two components in 2023, with one component moving at an apparent five times the speed of light (which is a known illusion called superluminal motion). That allowed the team to look into where and how the particles are being accelerated to extreme energies along the jet. | Press release

Watching a Black Hole Wind Grow: Chandra and Hubble Reveal the Early Stages of Galaxy

Anna Trindade Falcao (NASA Goddard SFC) presented combined Chandra and Hubble observations that may capture a supermassive black hole wind in its earliest stages of growth. Active galactic nucleus (AGN) feedback is thought to happen, but how it begins remains poorly understood. Studying two nearby quasars in which Chandra (tracing hot X-ray wind) and Hubble (tracing warm ionized gas) data are aligned, the team found that the hot and warm phases extend together and not independently. This would suggest a single multi-phase outflow. Their team proposed a four-stage sequence for AGN feedback and also argued that their two systems capture the earliest stages of that process. XRISM Reveals Changing Accretion-Driven Winds in a Nearby Active Galaxy:

Xin Xiang (University of Michigan) presented the most detailed X-ray portrait of the winds flowing out of NGC 4151, an active galaxy roughly 16 million light-years away with a 30-million-solar-mass black hole. Every major X-ray observatory has observed this galaxy before, but earlier instruments could not separate its multiple wind components. With the high-resolution X-Ray Imaging and Spectroscopy Mission (XRISM) spectrometer, Xiang resolved three wind populations by velocity: warm absorbers (100–1,000 km/s), very fast outflows (1,000–10,000 km/s), and ultra-fast outflows (over 10,000 km/s). Across 14 XRISM observations over a year, they found that the fast winds turn on three hours after each bright X-ray flare, matching the predicted timescale for magnetically driven wind. | Press release

NuSTAR Reveals a Significantly Variable Active Galactic Nucleus Corona

Xiurui Zhao (Caltech) presented the first observational evidence of significant temperature variation in the corona of an AGN. The corona produces about 90% of all X-ray photons from an AGN, but its temperature can only be measured with X-ray missions sensitive to high-energy spectral curvature like NASA’s NuSTAR. They compared NuSTAR’s observations across multiple years and found that despite having the same luminosity in 2015 and 2024, the 2024 corona was significantly cooler than the 2015 corona. In follow-up observations in 2025, it was back at its earlier temperature. This is the first clear observation of coronal temperature variability in an AGN. | Press release

New Surprises from Radio Observations of Tidal Disruption Event Outflows

Kate Alexander (University of Arizona) presented new radio observations of tidal disruption events (TDEs). TDEs occur roughly once every 100,000 years in a given galaxy. It happens when a star drifts too close to the black hole, is stretched and squeezed into a long stream of debris (a process astronomers call spaghettification) and some of that debris falls onto the black hole while the rest is thrown outward and lights up in radio. Alexander and her team used six years of Very Large Array monitoring of several dozen nearby TDEs. They found that many TDEs unexpectedly turn on in the radio years after the original event, even long after their optical light has faded. Their team combined radio data with X-ray and optical accretion-rate measurements and found that these late-time radio flares appear when the black hole is eating either very quickly or very slowly, but not at moderate rates! This pattern matched what is seen in stellar-mass black holes and this suggests that accretion physics may operate similarly across many orders of magnitude in black hole mass. | Press release

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Plenary Lecture: Mario Jurić, Early Results from the Rubin Observatory: Mapping the Solar System and Beyond (by Kerry Hensley)

Mario Jurić (University of Washington; PI of the University of Washington Rubin operations element) began by remarking on how our collective concept of what an astronomer is has been transformed over the past 25 years. While a Google image search for “astronomer” yields an array of people pointing small telescopes at the night sky, today’s version of professional astronomy looks quite different: huge telescopes with enormous cameras covering vast swaths of the sky, with analysis aided by software and data deposited in massive databases.

This rapid transition was first spurred by enterprises like the Sloan Digital Sky Survey, which collected 20 terabytes of raw data from 1.2 billion observations. Now, digital sky surveys are common, and they’re becoming ever larger. The next massive digital sky survey will be the Legacy Survey of Space and Time from the NSF–DOE Vera C. Rubin Observatory — an observatory that can “download the universe” and is poised to transform our understanding of everything from asteroids to dark energy.

Rubin released its first images on 23 June 2025, and among these stunning images is a broad view that contains thousands of galaxies in the Virgo cluster, a golden tangle of four colliding galaxies, a nearby galaxy cluster, a distant galaxy cluster, and a handful of nearby spiral galaxies bursting with star formation. As fantastic as this image is, Jurić emphasized that it’s just one still image in a movie: as Rubin returns to the same fields of view time and time again, it’ll spot things that change brightness (like variable stars and transients) and things that move (like asteroids).

Jurić highlighted four areas in which Rubin has already contributed greatly, focusing on discoveries within our solar system:

1. 1. Asteroid variability: Rubin has already collected hundreds of thousands of observations of asteroids, resulting in the discovery of extremely fast rotators like 2025 MN45, which must have an extremely high tensile strength not to fly apart.
   2. Observations of interstellar object 3I/ATLAS: During the observatory’s commissioning survey, the Rubin team realized that they had observed 3I/ATLAS before it was discovered — but in observations that were technically under embargo. Recognizing the high impact of the data, the team found a way to share their findings, leading the 150-person collaboration to write a paper on their findings in a mere three days.
   3. High-precision asteroid photometry: While analyzing the commissioning data, the Rubin team discovered systematic offsets in the positions of asteroids — but no other types of objects. They found that this effect varied across the sky and was worse in the south. They eventually discovered that because most asteroids are observed from the north, that catalogs of asteroid orbits are systematically biased at a level of 20-40 milliarcseconds. Luckily, Rubin will provide the much-needed southerly data necessary to clean up these catalogs within about a year.
   4. Outer solar system studies: Researchers discovered 380 new trans-Neptunian objects in Rubin’s commissioning data. (Compare that to just 5,000 known trans-Neptunian objects in total!) In the time since the commissioning data were collected, hundreds more candidate objects were discovered.

With such enormous data yields from Rubin, how do we efficiently turn data into science? Jurić outlined strategies for handling massive datasets using well-crafted data formats, computing tools, and AI. In particular, Jurić highlighted the Astronomical Catalog Inference Driver, or ACID, which he built in four weeks on his phone using Claude. The tool is comparable to “a product developed in >3 years by extremely capable human professionals” and can rapidly handle immense data tables, showing how AI can accelerate the development of tools to handle tomorrow’s datasets.

Read Astrobites’s interview with Mario Jurić.

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Plenary Lecture: Esra Bulbul, Cosmology and Baryons Across Scales: Probing Halo Mass Function to Cosmic Filaments with eROSITA (by Lexi Gault)

Esra Bulbul (Max Planck Institute for Extraterrestrial Physics) began her plenary talk at the beginning of time — the Big Bang marked the start of the universe, and from there we attempt to constrain cosmological parameters in order to understand how the universe was born and how it has evolved. Bulbul notes that a lot of work has been done to constrain cosmology from the cosmic microwave background (CMB), and we must compare those early time measurements to those from later times to build a full picture. In cosmology, tensions have arisen between early-time and late-time probes. CMB measurements of the Hubble constant and S8, the “clumpiness” parameter of the universe, do not agree with late time probes that find that the universe is accelerating faster with smaller fluctuations than the CMB predictions. How do we work toward resolving this tension?

The extended ROentgen Survey with an Imaging Telescope Array (eROSITA) is a space telescope that has performed the first imaging all-sky survey in the medium X-ray range, seeking to map the large-scale structures of the universe to better constrain cosmological constants. eROSITA focuses on finding galaxy groups and clusters via the hot X-ray gas within and between them across the last 5-7 billion years of the universe. Since its launch in 2019, eROSITA has completed more than four full-sky surveys. Of the million X-ray sources detected by eROSITA, only 12,247 (1%) are galaxy clusters and groups.

From the observed X-ray emission from the galaxy clusters and groups, the eROSITA team has been able to measure the temperature of the intercluster medium within the sample. Working with weak gravitational lensing surveys, they have been able to measure the masses of the newly discovered clusters and groups. These measurements show that eROSITA has detected sources across three orders of magnitude in mass, reaching from the galaxy level to large-scale clusters.

The galaxy cluster and group observations allow them to constrain a few cosmological parameters including S8 (density fluctuations), Ωm (matter density), and w0 (dark energy). From the impressive eROSITA data, Bulbul showed that they could constrain S8 and Ωm to five times better precision than ever before! These late-time results are fully consistent with what has been measured from the early-time CMB measurements. Additionally, the dark energy measurements agree with what has been measured thus far from the Dark Energy Spectroscopic Instrument survey.

Bulbul then switched us from the exciting cosmological results to those regarding baryon detection. A striking result from eROSITA was the detection of hot gas well beyond what is typically considered the gravitational extent of a galaxy cluster — reaching out to 16 million light-years, often larger than the galaxy cluster itself. This underscores the importance of X-ray surveys in detecting the very extended gas encapsulating the largest-scale structures of the universe.

Looking forward, Bulbul discussed the future work planned for eROSITA. Transitioning now to working with the deepest data of the survey, the team expects to find about 40,000 galaxy clusters with about half of those being used for cosmology. They anticipate obtaining even higher precision on cosmological parameter measurements, comparable to that obtained from CMB observations. The work of eROSITA is revolutionizing cosmology at later times in the universe, and the future is exciting.

Read Astrobites’s interview with Esra Bulbul.

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The post AAS 248: Day 1 appeared first on AAS Nova.

The Transient Artifact and Continuous Learning System (TACLS) leverages data from continuously operating satellite networks coupled with machine learning models to help meteorologists at the National Weather Service forecast flash floods more efficiently. This new software is the result of a collaboration between NASA’s Jet Propulsion Laboratory, the University of California, San Diego (UCSD), and the National Oceanic and Atmospheric Administration (NOAA) National Weather Service (NWS).

Created with support from NASA’s Earth Science Technology Office (ESTO), TACLS leverages machine learning to automatically locate evidence (unusual increases in atmospheric moisture) of impending flash flooding that meteorologists may otherwise miss as they analyze large amounts of data. TACLS flags that evidence, indicates where flash flooding could likely occur, and displays that information via a user-friendly visualization for human analysts to interpret. Those analysts can then decide whether to issue a flash flood warning or weather advisory.

This novel framework for tracking extreme weather events and predicting imminent flash floods operates in near real-time, producing forecasts in as little as fifteen minutes.

“That’s really what we wanted to do, to give meteorologists a tool to help decision making for flash flood warnings,” said Yehuda Bock, Distinguished Researcher at the UCSD Scripps Institution of Oceanography and principal investigator for TACLS.

In simulations testing, TACLS used data from diverse severe weather events—including atmospheric rivers, monsoonal convection, and tropical cyclone remnants—between 2017 and 2023 and successfully captured 93% of the issued flash-flood warnings. Meteorologists from the National Weather Service are currently working to incorporate TACLS into their existing systems for forecasting flash floods in Southern California.

This learning system has two main components. First, an analytic back-end software suite uses machine learning algorithms to process satellite data and determine areas at risk for flooding. Second, user-friendly visualization software highlights those areas for further analysis by humans.

The ACLS back-end software analyzes data from satellites in the Global Navigation Satellite System (GNSS), a constellation of satellite networks that drive navigation services around the world. Water vapor in the troposphere delays signals from these satellites as they travel to Earth. This signal delay can be analyzed to calculate the amount of water vapor in the atmosphere over a particular location on Earth.

The TACLS analytic back-end software suite features a machine learning model trained using more than 30 years of past GNSS data. This model is an anomaly detector that tracks unusual increases in atmospheric moisture. The model then carefully examines that atmospheric moisture data and determines whether it’s either an artifact (a false feature or distortion in the data) or a transient (a time-sensitive physical event, like heavy precipitation) that requires interpretation by human analysts.

If TACLS determines the data represents a transient, such as an extreme weather event that warrants a flash flood warning, it will forward that data to the TACLS visualization software (MGViz) for further evaluation by humans. The analysts use their judgement and experience to interpret these events and determine whether the flagged data indicates a flash flood is likely, and, if necessary, issue a flash flood warning.

Several past innovations developed at JPL are leveraged by TACLS to process GNSS data and present the results. The analytic back-end software suite incorporates elements from JPL’s Domain-agnostic Outlier Ranking Algorithms program and the Time-series Forecasting, Evaluation, and Deployment program. The TACLS visualizer is based on the Multi-Mission Geographic Information System, originally developed at JPL for NASA’s Mars missions.

The TACLS software binds all these components within a novel system that enhances existing methods to reduce the amount of time it takes for a human analyst to determine whether to issue a flash flood warning.

Both the TACLS software and the data used to train it will be open-source, allowing scientists to either tailor this model in response to their unique research needs or create their own model from scratch.

For additional details, see the entry for this project on NASA TechPort. 

Project Lead: Dr. Yehuda Bock, University of California, San Diego. 

Sponsoring Organization(s): NASA’s Earth Science Technology Office Advanced Information Systems Technology Program; JPL; NOAA; National Weather Service. 

The Transient Artifact and Continuous Learning System (TACLS) leverages data from continuously operating satellite networks coupled with machine learning models to help meteorologists at the National Weather Service forecast flash floods more efficiently. This new software is the result of a collaboration between NASA’s Jet Propulsion Laboratory, the University of California, San Diego (UCSD), and the National Oceanic and Atmospheric Administration (NOAA) National Weather Service (NWS).

Created with support from NASA’s Earth Science Technology Office (ESTO), TACLS leverages machine learning to automatically locate evidence (unusual increases in atmospheric moisture) of impending flash flooding that meteorologists may otherwise miss as they analyze large amounts of data. TACLS flags that evidence, indicates where flash flooding could likely occur, and displays that information via a user-friendly visualization for human analysts to interpret. Those analysts can then decide whether to issue a flash flood warning or weather advisory.

This novel framework for tracking extreme weather events and predicting imminent flash floods operates in near real-time, producing forecasts in as little as fifteen minutes.

“That’s really what we wanted to do, to give meteorologists a tool to help decision making for flash flood warnings,” said Yehuda Bock, Distinguished Researcher at the UCSD Scripps Institution of Oceanography and principal investigator for TACLS.

In simulations testing, TACLS used data from diverse severe weather events—including atmospheric rivers, monsoonal convection, and tropical cyclone remnants—between 2017 and 2023 and successfully captured 93% of the issued flash-flood warnings. Meteorologists from the National Weather Service are currently working to incorporate TACLS into their existing systems for forecasting flash floods in Southern California.

This learning system has two main components. First, an analytic back-end software suite uses machine learning algorithms to process satellite data and determine areas at risk for flooding. Second, user-friendly visualization software highlights those areas for further analysis by humans.

The ACLS back-end software analyzes data from satellites in the Global Navigation Satellite System (GNSS), a constellation of satellite networks that drive navigation services around the world. Water vapor in the troposphere delays signals from these satellites as they travel to Earth. This signal delay can be analyzed to calculate the amount of water vapor in the atmosphere over a particular location on Earth.

The TACLS analytic back-end software suite features a machine learning model trained using more than 30 years of past GNSS data. This model is an anomaly detector that tracks unusual increases in atmospheric moisture. The model then carefully examines that atmospheric moisture data and determines whether it’s either an artifact (a false feature or distortion in the data) or a transient (a time-sensitive physical event, like heavy precipitation) that requires interpretation by human analysts.

If TACLS determines the data represents a transient, such as an extreme weather event that warrants a flash flood warning, it will forward that data to the TACLS visualization software (MGViz) for further evaluation by humans. The analysts use their judgement and experience to interpret these events and determine whether the flagged data indicates a flash flood is likely, and, if necessary, issue a flash flood warning.

Several past innovations developed at JPL are leveraged by TACLS to process GNSS data and present the results. The analytic back-end software suite incorporates elements from JPL’s Domain-agnostic Outlier Ranking Algorithms program and the Time-series Forecasting, Evaluation, and Deployment program. The TACLS visualizer is based on the Multi-Mission Geographic Information System, originally developed at JPL for NASA’s Mars missions.

The TACLS software binds all these components within a novel system that enhances existing methods to reduce the amount of time it takes for a human analyst to determine whether to issue a flash flood warning.

Both the TACLS software and the data used to train it will be open-source, allowing scientists to either tailor this model in response to their unique research needs or create their own model from scratch.

For additional details, see the entry for this project on NASA TechPort. 

Project Lead: Dr. Yehuda Bock, University of California, San Diego. 

Sponsoring Organization(s): NASA’s Earth Science Technology Office Advanced Information Systems Technology Program; JPL; NOAA; National Weather Service. 

The post NASA Uses Machine Learning to Enhance Flash Flood Warnings appeared first on NASA Science.