It feels like there's no escaping AI right now, whether you’re trying to type a sentence without being interrupted by a digital “assistant” or struggling to find a new refrigerator that doesn’t require a Wi-Fi connection for some reason. You’d be forgiven for wondering if we’re in the midst of a quantum leap in tech or whether people are just hyping up a heap of slop.

So what should we make of the growing use of AI in weather and climate modeling?

The conversation didn't get off to a great start earlier this year when a National Weather Service office posted a forecast map featuring nonexistent cities in Idaho with names like “Whata Bod” and “Orangeotild.” Thankfully, that was just an AI-generated image produced for social media, not the actual forecast model. Meteorologists and climate scientists are not yet being replaced by large language model prompt engineers.

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When the third known object from the galactic space beyond our Sun barreled through the solar system last year, Earth was in a terrible spot to view its flyby. Thankfully, however, a spacecraft that was previously busy mapping Mars took advantage of much better positioning for a closer look.

Cheap Seats

Astronomers have now observed three interstellar objects as they’ve flown through the solar system: 1I/ʻOumuamua, which shocked astronomers in 2017; 2I/Borisov, which followed in 2019 and behaved almost identically to a solar system comet; and now 3I/ATLAS, which was found buzzing toward the Sun in July 2025. As soon as 3I/ATLAS was spotted, pretty much every telescope on the planet took a look. The data swiftly revealed much that intrigued astronomers: while 3I/ATLAS was behaving essentially like a standard comet, its chemistry was nothing like its solar system counterparts, and its coma and dust outflow were strangely shaped. Among other oddities, it seemed to counterintuitively have a dust tail that pointed toward the Sun.

Unfortunately for astronomers, 3I/ATLAS didn’t make it easy for them to study the shape of its coma. Thanks to a cosmic coincidence, the interstellar visitor was traveling almost perfectly within the plane of our solar system, and Earthbound observers were often limited to an edge-on view of its tail. Even worse, 3I/ATLAS looped around the back of the Sun from our perspective, meaning no one on the planet could observe the comet for a few weeks in the fall. This led a group of astronomers to consider their assets that are farther from home.

Better View from Mars

The Tianwen-1 spacecraft, which entered Martian orbit in early 2021 and has been diligently mapping the Red Planet ever since, has a high-resolution camera that’s normally pointed at the planet’s surface. By spinning the spacecraft around, a team of researchers led by Xin Ren (National Astronomical Observatories, Chinese Academy of Sciences) repurposed the camera to act as a small telescope when 3I/ATLAS flew by. In another cosmic coincidence, 3I/ATLAS happened to pass very near Mars last fall, and this close approach gave Tianwen-1 a great out-of-plane view of the coma. The orbiter managed to capture 57 images of 3I/ATLAS over three days last fall, representing China’s first-ever observations of an object from an asset in deep space.

The team took full advantage of the great view and leveraged the spacecraft’s unique perspective to extract some intriguing results. By tracking how the gentle pressure of sunlight nudged the escaping grains, the researchers found that the coma is dominated by surprisingly large dust. With an average size of hundreds of microns across, the dust is more like coarse sand than smoke, and they found that it ambles away from the comet at just 3–10 meters per second. All told, 3I/ATLAS was shedding dust at roughly 1,000 kilograms every second. The big grains may be a fingerprint of a cold, distant birthplace: models suggest such grains collect in the frigid outer reaches of planet-forming disks, hinting that 3I/ATLAS was forged far from its parent star before being flung into the dark.

As new surveys begin to turn up interstellar interlopers more often, this improvised observation makes a tidy point: the spacecraft already scattered across the solar system can double as a fleet of opportunistic comet-watchers, each offering a view we simply can’t get from home.

Citation

“Interstellar Object 3I/ATLAS Observed from Mars by China’s Tianwen-1 Spacecraft,” Xin Ren et al 2026 ApJL 1003 L10. doi:10.3847/2041-8213/ae61b3

The post Courtside Seats on Mars appeared first on AAS Nova.

Planets that get too close to their host stars are liable to be engulfed and consumed. New research explores how to identify stars that have had a planetary snack.

It’s Snack Time

Being a planet that closely orbits its star is dangerous, and various dynamical processes can draw a planet inward past the point of no return. When a planet vanishes beneath the surface of its host, it eventually disintegrates within the star, its atoms mixing into the blazing stellar soup.

This outcome is likely extremely common across the universe, and researchers have begun to see evidence for it: stars that appear to have absorbed angular momentum from their planets, white dwarfs with uncanny metals in their spectra, and stars with chemical abundances that don’t match those of their siblings. Now, in a recent publication led by Kaitlyn Lane (Vanderbilt University), researchers seek to find observational signatures of planetary engulfment of rocky exoplanets by main-sequence stars.

Modeling Engulfment

Lane’s team focused on main-sequence stars in the range of 0.5 to 1.4 solar masses, using one-dimensional analytical models to determine which of these stars will most readily display signs of having engulfed a planet. They simulated the stars as they consumed either an Earth-like planet or a super-Earth with the same composition as Earth but 15 times its mass.

At the onset of the model, the engulfment is set to begin, the planet placed tangent to the star’s surface. The planets sink down and orbit just barely within their stars for 1–10 years, their solid surfaces slowly beginning to evaporate.

After that relatively lengthy phase, the process proceeds rapidly: as the planet inches deeper into its star, the drag forces grow stronger and the planet’s demise accelerates, with the planet disintegrating over the course of hours. In the last phase, the planet makes its final plunge and is destroyed in a half hour.

Signs of Planets Past

Lane’s team found that the planets tended to be destroyed fully within the outer convective layer of their stars, except in the case of the most massive stars studied here. For more massive stars, the outer convective zone is shallower than it is for the less massive stars, allowing a chunk of each planet to survive the passage through the convective zone to reach the radiative zone below.

What this translates to, for the purposes of identifying planet-eating stars from afar, is that stars near the top of the mass range studied — from 1.0 to 1.4 solar masses — make the best targets. This is because the tell-tale planetary metals are not overly diluted within the stars’ relatively small convective zones, making these elements easier to detect. In terms of specific metals, the authors found that aluminum, calcium, and vanadium are the best signposts of planetary engulfment, with lithium also making the list.

While the authors acknowledge that there’s more work to be done — they plan to investigate the impacts of planetary engulfment on stellar structure more closely, for example — this work represents an important foray into identifying targets for future studies of stars that have eaten their planets.

Citation

“Observable Metal Pollution in Main-Sequence Stars: Simulations of Rocky Planets Engulfed by Stars in the 0.5 to 1.4 M_⊙ Range,” Kaitlyn T. Lane et al 2026 ApJ 1003 67. doi:10.3847/1538-4357/ae5b9a

The post Now That’s Metal: How to Spot Stars That Have Swallowed Their Planets appeared first on AAS Nova.

The fastest spinning pulsars in the universe are often quite difficult to detect. Leveraging multiple observations from the largest single-dish telescope in the world, researchers have discovered six previously undetected pulsars.

Millisecond Pulsars in Globular Clusters

Globular clusters, compact collections of tens of thousands to millions of stars, are highly dense and rife with dynamical interactions. These active environments are ideal factories for the formation of millisecond pulsars — the extremely fast-spinning cores of once-massive stars, shining beams of radio emission from their poles. One way millisecond pulsars are thought to form is when a pulsar in a binary system steals mass from its companion star, transferring angular momentum and causing the pulsar to spin up. The densely packed environment in a globular cluster provides ample opportunity for a pulsar to acquire a companion to siphon.

However, millisecond pulsars in distant globular clusters are notoriously difficult to detect. Traditional pulsar searches that rely on a single observation tend to miss millisecond pulsars, many of which have signals too faint to be distinguished from noise or radio interference. Instead, researchers must rely on a different method to find these fast-spinning pulsars.

Stack Search Success

To find faint millisecond pulsars, researchers have developed the stack search method, in which multiple radio observations are combined to tease out faint signals and decrease noise. Reliably stacking observations across epochs requires stability; isolated millisecond pulsars, now no longer spinning up after losing their companion, have very stable rotation periods, making them ideal targets for the stack search method. To date, the stack search method has successfully identified nine isolated globular cluster millisecond pulsars using data from the Arecibo, Parkes, and Green Bank radio telescopes.

In hopes of recovering more of these faint fast-spinning pulsars, Yinfeng Dai (Beijing Normal University) and collaborators used archival data obtained with the Five-hundred-meter Aperture Spherical radio Telescope (FAST), the world’s largest single-dish telescope. Targeting two specific globular clusters, NGC 6517 and M15, the team applied the stack search method to 23 and 19 observations of the globular clusters, respectively. From their search, the authors discovered six previously unidentified isolated millisecond pulsars: four in NGC 6517 and two in M15.

While previous studies identified brighter pulsars in the targeted globular clusters, the authors confirmed that all six newly discovered pulsars are too weak to be reliably recovered from single-epoch searches, underscoring the importance of the stack search method. In particular, this search increased the known pulsar populations of NGC 6517 and M15 by 27% and 18%, respectively, suggesting that a meaningful fraction of globular cluster pulsars are easily missed in traditional pulsar searches. Future studies employing this stack search method will continue to detect faint millisecond pulsars, unlocking this elusive population for further exploration.

Citation

“The Stack Search Tests on FAST Data: Discovery of Six Faint Isolated Millisecond Pulsars in NGC 6517 and NGC 7078 (M15),” Yinfeng Dai et al 2026 ApJL 1002 L31. doi:10.3847/2041-8213/ae5dbb

The post Stacking Up the Discovery of Six Millisecond Pulsars appeared first on AAS Nova.

Where do black hole mergers happen? Recent research finds evidence that most black hole mergers occur in triple systems containing a close inner binary and a more distant third party.

Assembling Merging Black Holes

Thanks to the combined efforts of the LIGO, Virgo, and KAGRA gravitational wave detectors, we’ve now collected the subtle signals from several hundred pairs of merging stellar-mass black holes. As this collection of spacetime ripples continues to grow, researchers are seeking to understand how these merging black hole pairs were assembled.

In the simplest scenario, pairs of high-mass stars independently evolve into black holes, lose momentum by emitting gravitational waves, and meld into one another. But the population of merging black holes likely contains contributions from multiple sources, including multiple-star systems, the disks surrounding accreting supermassive black holes, and black holes that have already experienced a merger. Which of these merging populations is reflected in our catalog of gravitational wave events?

Modeling Challenges

In theory, this question can be answered by extracting the properties of merging black holes — mass, spin, and the like — from gravitational wave observations and comparing these properties against model predictions from different formation pathways. In reality, this is exceedingly difficult, as certain merger pathways can produce a wide variety of results, depending on assumptions or fine tuning.

So far, the increasingly large pool of gravitational wave detections tentatively points to a feature that could illuminate the sites of black hole mergers: a peak in the spin–orbit tilt distribution around 90 degrees. This feature has been most confidently extracted from nonparametric analyses, which do not make assumptions about the population of merging black holes, but it has also been hinted at in parametric analyses, which do make population-level assumptions.

Triple-System Feature

To investigate this feature further, a team led by Jakob Stegmann (Max Planck Institute for Astrophysics) performed a new, astrophysically motivated parametric analysis of the most recent catalog of gravitational wave detections from LIGO, Virgo, and KAGRA.

Their modeling tests combinations of multiple populations, including mergers in isolated binary systems, triple-star systems, and dense environments like star clusters. They also include a potential contribution from higher-mass mergers involving black holes that have merged previously. Using this framework, Stegmann’s team found that the observed spin–orbit tilt distribution is best matched by a model dominated by mergers in triple-star systems, with some contribution from other sources. Specifically, this finding suggests that most mergers occur in hierarchical triple systems, which naturally predict an excess of 90-degree spin–orbit tilts without any fine tuning. Hierarchical triples contain an inner close binary with a distant outer companion; in these systems, relativistic spin precession, gravitational wave emission, and oscillations in eccentricity and inclination work to tilt the black holes in the inner binary by 90 degrees.

Stegmann and collaborators pointed out that the triple-system scenario aligns well with other properties of the observed population of black hole mergers, such as the mass and effective spin distributions. This scenario may also be necessary to explain certain merging pairs that might have had slightly eccentric orbits at the moment of merging. If future gravitational wave observations strengthen the evidence for a peak in the spin–orbit tilt distribution near 90 degrees, it will have profound implications for how and where black holes merge in our universe.

Citation

“Gravitational-Wave Observations Suggest Most Black Hole Mergers Form in Triples,” Jakob Stegmann et al 2026 ApJL 1000 L59. doi:10.3847/2041-8213/ae52ec

The post Third Star’s the Charm: Most Merging Black Holes Might Be in Triple Systems appeared first on AAS Nova.

Each Jupiter-size planet in the galaxy falls into one of three distinct categories: hot, warm, or cold. A new study suggests that despite the apparent differences between these populations, they may have all formed from the same underlying dynamical process: a game of pool played at planetary scales.

A Diversity of Jupiters

Though our solar system has only one Jupiter-size planet, elsewhere in the galaxy we have found three different species of these massive gas giants. Cold Jupiters closely resemble their namesake and orbit far from their host stars; hot Jupiters are the opposite and are found whipping around their stars on extremely close-in orbits. In between these are the warm Jupiters, which tend to orbit in the intermediate space between 0.1 and 1.0 au.

Though these three populations are defined by their orbital distances, they differ from each other in other ways as well. For example, hot Jupiters almost never have nearby companions; if there are any other planets circling the same star, they’re usually far-out cold Jupiters. They can also orbit in pretty much any direction, including opposite the direction of their star’s spin, and are usually on perfectly circular orbits. In contrast, warm Jupiters often have friends nearby, are much more aligned with their stars’ spins, and can have modest eccentricities.

Given these differences, it’s often thought that each of these populations arrived at its current location through different dynamical processes and that the history of the warm Jupiters is likely quite different from the history of the hot Jupiters. However, a new study led by Julia Esposito (Georgia Institute of Technology) has proposed an alternative view. Maybe these populations, though they appear different now, were all created by the same process: planet–planet scattering.

Virtual Planetary Billiards

Esposito and collaborators set up 1,500 virtual planetary systems with three massive planets each, then simulated how the orbits evolved before probing the final configurations. In crucial contrast to previous simulation studies, the team initialized their Jupiters across a range of different distances and included the effects of tides sapping energy from orbits of planets that got too close to their host stars.

At the end of the simulation, the team surveyed the digital carnage. Almost every virtual system ended with only two planets after either ejecting one away from the star or having two planets collide. But, remarkably, the remaining two-planet systems looked tantalizingly similar to what we actually observe, with a mix of hot, warm, and cold Jupiters. Even more exciting, the end populations were highly correlated to where the violent scattering event took place.

For example, the warm Jupiters were almost all produced by “warm scattering” simulations, where the scattering took place between 0.1 and 1.0 au. The planets that survived the simulations and ended up as warm Jupiters matched all of the properties of the real warm Jupiter population: they had nearby companions, were moderately eccentric, and were mostly aligned with their stars. The hot Jupiters, meanwhile, were almost all produced by “cold scattering” events where the flybys happened far from the star and resulted in one planet hurtling inwards. These also matched all of the observed properties of real hot Jupiters.

The researchers concluded that planet–planet scattering can produce both the warm and hot Jupiter populations so long as you let the planets scatter from a variety of different distances. This exciting theoretical insight, if correct, would mean that astronomers could stop searching for different pathways to create each population. Happily, this model also provides testable predictions, and the authors lay out how the theory could be supported or disproven with additional data. Through virtual experiments like these, astronomers continue to build up an understanding of how the wide range of planetary architectures observed across the galaxy came to be.

Citation

“Unified Formation Channel of Hot and Warm Jupiters via Planet–Planet Scattering,” Julia Esposito et al 2026 ApJL 1003 L3. doi:10.3847/2041-8213/ae61b0

The post Playing Pool with Planets appeared first on AAS Nova.

Discovered in December 2024, the roughly 60-meter-wide asteroid 2024 YR4 was initially thought to have a slim chance of striking Earth in 2032. Further observations ruled out an Earth impact but left open the possibility of a Moon impact. New JWST observations show that 2024 YR4 will speed past both Earth and the Moon without a collision.

Another Update on 2024 YR4

In April 2025, we featured a Research Note that described March 2025 JWST observations of 2024 YR4 and characterized the asteroid’s size and albedo. At the close of that article, the authors suggested that further JWST observations in early 2026 could help to refine our understanding of the asteroid’s trajectory and determine whether it would strike the Moon.

On 18 and 26 February 2026, JWST carried out those critical observations. In this dataset, the asteroid is bright enough to be detected confidently, and the background is peppered with a sufficient number of reference stars — two factors necessary to determine the precise track of the asteroid as it zipped through space.

Trajectory Refinement

Julien de Wit (Massachusetts Institute of Technology) and collaborators analyzed the new JWST data and determined the asteroid’s position. The team used multiple methods to reduce the data and showed that their results were consistent regardless of the reduction method, ultimately yielding a measurement with an uncertainty of just 50 milliarcseconds. This is a huge improvement over the previous trajectory estimate, which had an uncertainty of 700 milliarcseconds.

Combining the latest JWST observations with existing data stretching back to the asteroid’s discovery, de Wit and coauthors determined a new, highly precise orbit for the object — one that definitively shows that the asteroid will safely pass by the Moon at a distance of 22,900 ± 800 km in 2032. In addition to ruling out the upcoming lunar impact, the team also ruled out any collisions with Earth in the next 100 years. Phew!

High-Impact Science

This work highlights JWST’s potential as a tool for planetary defense. The February 2026 observations detailed here represent the faintest-ever detection of a near-Earth object, and JWST can detect objects far fainter than ground-based telescopes can. This ability allows JWST to observe potentially hazardous asteroids over a larger swath of their orbits, which translates to earlier trajectory estimation — JWST pinned down 2024 YR4’s orbit two years before the asteroid would have become bright enough for ground-based telescopes to do so.

JWST’s role may be even more important for smaller objects that rapidly become undetectable after discovery. De Wit’s team demonstrated this for a 10-meter-diameter 2024 YR4 clone on the same trajectory; for an object of this size, JWST would be able to rule out an Earth impact before the asteroid became undetectable, but ground-based telescopes could not. With surveys from facilities like Vera C. Rubin Observatory and Near-Earth Object Surveyor set to discover hundreds of thousands of new near-Earth objects, JWST’s role as a hazard assessor will likely be in high demand.

Citation

“JWST Observations of Asteroid 2024 YR4 Rule Out a 2032 Lunar Impact and Demonstrate a New Regime for Planetary Defense Follow-Up,” Julien de Wit et al 2026 ApJL 1003 L21. doi:10.3847/2041-8213/ae6a95

The post Asteroid 2024 YR4 Won’t Hit the Moon, New JWST Observations Show appeared first on AAS Nova.

How do massive galaxies form and evolve? A recent study traces the stellar and dust distributions across evolutionary phases of massive galaxies to better understand how massive dusty star-forming galaxies fit into the picture.

Dusty Massive Galaxies

Massive galaxies, like the Milky Way or even larger, undergo phases of active star formation and quiescent phases of inactivity, but exactly how these galaxies evolve through these stages is not yet fully understood. Dusty star-forming galaxies, which are undergoing a period of intense star formation and shrouded in dust, might be the missing evolutionary step between star-forming and quiescent phases of massive galaxy evolution. 

Currently, the leading explanation for massive galaxy formation and evolution is inside-out growth — star formation and quenching start in the inner regions of a galaxy and progress outward. However, it’s not clear whether dusty star-forming galaxies also follow the favored inside-out pathway, or if they instead proceed outside-in, first growing their disks and then assembling a central bulge.

The spatial distribution (or morphology) of the stars and dust within dusty massive galaxies can help us trace their evolution. Thanks to high-resolution observations from JWST and the Atacama Large Millimeter/submillimeter Array (ALMA), researchers can now directly compare the morphologies of distant star-forming, quiescent, and dusty galaxies during the height of our universe’s star formation. Filling this gap will reveal how dusty star-forming galaxies may connect star-forming and quiescent galaxies in massive galaxy evolution.

Multiwavelength Morphological Comparisons

To directly compare the star and dust morphologies across massive galaxies, Sarah Bodansky (University of Massachusetts, Amherst) and collaborators selected a sample of 33 dusty star-forming galaxies from the GOODS-ALMA 2.0 survey that searched the sky for 1.1-mm dust emission as well as star-forming and quiescent comparison samples drawn from JWST observations. Combining the ALMA survey data with JWST imaging, the authors studied the rest-frame optical (stars) and rest-frame near-infrared (dust) morphologies of dusty, star-forming, and quiescent galaxies at redshifts around cosmic noon (a few billion years after the Big Bang).

When comparing optical morphologies, the authors found that dusty star-forming galaxies and typical star-forming galaxies had similar distributions, but their near-infrared morphologies showed clear differences. Dusty galaxies tended to show more compact near-infrared emission, with dust tracing their stellar populations and more concentrated in the galaxies’ central regions. Though clearly different from star-forming galaxies, the authors noted striking similarities between the near-infrared morphologies of the dusty star-forming and quiescent galaxies, especially within their centers.

All of these properties suggest that dusty star-forming galaxies have built up stellar mass and dust in their cores, potentially forming a central bulge first and supporting an inside-out model of massive galaxy growth. This points to dusty star-forming galaxies as possible direct progenitors of early massive quiescent galaxies, hanging onto their last bit of star formation before becoming quiet as well. While this study morphologically distinguishes dusty galaxies from their star-forming and quiescent counterparts, future spectroscopic studies comparing the kinematics of these populations and investigations of molecular gas distributions are necessary to better pin down the evolutionary connection between star-forming, dusty, and quiescent massive galaxies.

Citation

“JWST+ALMA Reveal the Buildup of Stellar Mass in the Cores of Dusty Star-forming Galaxies at Cosmic Noon,” Sarah Bodansky et al 2026 ApJ 1001 235. doi:10.3847/1538-4357/ae4f64

The post Hints for Massive Galaxy Evolution from Dusty Star-Forming Galaxies appeared first on AAS Nova.

The NSF–DOE Vera C. Rubin Observatory has yet to begin its 10-year Legacy Survey of Space and Time, but it’s already keeping an eye on the sky. Astronomers recently described Rubin’s serendipitous spotting of 3I/ATLAS days before the interstellar object’s discovery.

Welcome, 3I/ATLAS

Our solar system has been playing host to a rare interstellar tourist: 3I/ATLAS. Just the third known interstellar object to have passed through our star system, 3I/ATLAS was discovered on 1 July 2025 by the robotic telescope network of the Asteroid Terrestrial-impact Last Alert System (ATLAS). After making its closest approach to the Sun in October 2025, 3I/ATLAS is now journeying out of the solar system and is currently located beyond the orbit of Jupiter.

While astronomers would likely grumble about hosting a human guest for nearly a year, they’ve been thrilled with 3I/ATLAS’s lengthy visit and have turned countless telescopes toward the rare interstellar object. They’ve also turned to the archives, searching for pre-discovery sightings of the object — and finding them in the commissioning data from one of the most highly anticipated observatories on the planet: Rubin Observatory.

A Serendipitous Sight

In the months since the release of Rubin’s exceptional first images, its 8.4-meter telescope and array of instruments have undergone rigorous testing to ensure they can meet the high standards required for the upcoming survey.

For most of 2025, Rubin was in its commissioning phase, carrying out science validation observations — a critical period during which instruments, procedures, and pipelines are fine tuned, and the quality and quantity of data collection can vary. On 20 June 2025, the very first night of its science validation survey, Rubin happened to turn toward the small patch of sky containing the as-yet undiscovered 3I/ATLAS.

More to Come

In a recent article, Colin Orion Chandler (LSST Interdisciplinary Network for Collaboration and Computing Frameworks; University of Washington) and collaborators described how they tracked down 3I/ATLAS in Rubin’s commissioning data after the object’s discovery was announced. In total, the observatory serendipitously spotted 3I/ATLAS nine times between 21 June and 2 July, then several more times — some on purpose, some by chance — between 3 and 20 July.

Analyzing Rubin’s observations of 3I/ATLAS required the development of custom techniques, since the observatory’s pipeline for handling observations of rapidly moving solar system objects was not in operation at that time. Despite these challenges, Chandler’s team successfully made astrometric measurements, collected photometry, determined 3I/ATLAS’s orbit, and studied the comet’s structure and nucleus. Among other findings, these data clearly show the presence of the object’s fuzzy coma, providing the earliest high-resolution evidence of cometary activity.

In their analysis of Rubin’s observations of 3I/ATLAS, Chandler and collaborators found that had the science validation survey started sooner, and had the analysis pipelines been operational, Rubin might have been the first to welcome humanity’s third interstellar visitor. Findings like these heighten the anticipation for the start of the Legacy Survey of Space and Time, during which Rubin will surely build upon its already impressive record of interstellar object observations.

Citation

“NSF-DOE Vera C. Rubin Observatory Observations of Interstellar Comet 3I/ATLAS (C/2025 N1),” Colin Orion Chandler et al 2026 ApJL 1001 L35. doi:10.3847/2041-8213/ae4b3a

The post Interstellar Comet 3I/ATLAS Through the Eyes of Rubin Observatory appeared first on AAS Nova.

The core of the brightest galaxy in the cluster Abell 402 contains a curious void. New observations suggest that an ultra-massive black hole could have excavated this feature.

At the Center of the Center of a Cluster

Abell 402 is a galaxy cluster located roughly 4 billion light-years away, and at its center is a giant elliptical galaxy called A402-BCG. Zooming in on the heart of this galaxy, astronomers using the Hubble Space Telescope discovered a dark region that they suspected was due to a cloud of dust blocking the starlight from the galaxy’s center.

In a recent research article, a team led by Michael McDonald (Massachusetts Institute of Technology) investigated this dark region to test the dust-cloud hypothesis and explore other explanations.

McDonald’s team compiled new JWST Near-Infrared Camera data, archival Hubble imaging, and spectroscopy from the Multi Unit Spectroscopic Explorer (MUSE) on the Very Large Telescope. The new JWST images show a prominent dark feature at the center of A402-BCG, plus a bright source directly beside it.

Not Hidden, but Missing

If the dark feature at the center of A402-BCG is a dust cloud, the cloud would be less obscuring at the near-infrared wavelengths captured by JWST than at the optical wavelengths sampled by Hubble. However, the feature was equally dark in the JWST images, leading the team to rule out the dust-cloud hypothesis.

Instead, they favor a scenario in which the dark feature is due to an absence of stars rather than the presence of obscuring dust. The team estimated that 2 billion solar masses of stars are missing — equivalent to 1% of the stellar mass of the galaxy. What’s more, the cavity is situated in a larger region of constant surface brightness called a core, in which there are fewer stars than expected.

The Dynamical History of A402-BCG

McDonald and coauthors suggested that the missing stars in A402-BCG’s core and cavity were ejected by at least one supermassive black hole binary. They estimated that the core region, which is roughly 6,500 light-years across, was excavated by a 50 billion solar mass black hole. This epic black hole may be the result of a past merger and is likely located at the infrared-bright spot on the border of the cavity, as this source’s spectral energy distribution resembles that of an actively accreting black hole.

MUSE spectroscopy provided evidence for a second black hole. These data revealed two pockets of ionized gas — one coincident with the infrared-bright source, the other on the opposite side of the cavity — as well as two distinct sets of emission lines consistent with a black hole binary totaling 60 ± 20 billion solar masses. (The team noted that alternate explanations for the second source, like a compact starburst, were less likely but couldn’t be ruled out.)

The team favors a scenario in which these black holes are slowly spiraling toward one another, ejecting stars from the galaxy’s center as they move and carving out a deep deficit of stars. This stellar cavity sits within a larger region of stellar scarcity that was scooped out by a past supermassive black hole merger that created the ultra-massive black hole present in the galaxy today. Simulations suggest that only about 0.5% of massive galaxies are in this phase of evolution at a time, so we may have caught A402-BCG in a fascinating moment — one that provides new clues about how to search for ongoing black hole mergers in other galaxies.

Citation

“A Kiloparsec-Scale Stellar Cavity in the Center of A402-BCG May Be Caused by Dynamic Interactions with an Ultramassive Black Hole,” Michael McDonald et al 2026 ApJL 1002 L19. doi:10.3847/2041-8213/ae5bbe

The post Into the Void: Investigating the Heart of a Giant Elliptical Galaxy appeared first on AAS Nova.

The Sloan Digital Sky Survey (SDSS) fundamentally changed the way modern astronomy research is done. This “grand and bold thing” is not frozen in a museum exhibit, however: instead, the SDSS telescopes and team have continued to iterate. The collaboration recently described the fifth generation of this groundbreaking survey in The Astronomical Journal.

Roots in History

Astronomy is now without question a “big data” science. While a lucky few researchers still occasionally travel to distant mountaintops to sojourn with the stars, most astronomers who can describe their work as “observational” rarely ever leave their laptops. Petabytes of historical data, including images, spectra, enormous simulation archives, and more, are available the instant one’s fingers touch a keyboard. As a result, the speed of discovery has increased exponentially, and the barriers to cutting-edge research have dramatically shrunk.

While no paradigm shift can be pinned to an exact date, astronomy’s turn towards the data-rich era arguably began in 1998 when SDSS first began collecting data. This was among the first of the “industrial” surveys that observed large swaths of the sky with electronic detectors and used automated pipelines for bulk data processing. In the years since, larger robotic telescopes have begun to mimic the SDSS strategy of “mowing the sky.” The latest of these successors, which itself may usher in another paradigm shift in terms of data volume and availability, is the soon-to-begin Legacy Survey of Space and Time at the Vera C. Rubin Observatory.

While SDSS’s twin 2.5-meter telescopes (one in New Mexico and one in Chile, allowing the survey to observe the entire sky) are dwarfed by Rubin’s 8-meter mirror, there is still thrilling science to be done with these moderate-sized observatories. This is especially true after a series of upgrades to the spectrographs and thanks to a deep expertise in not only survey-style science, but also in project management and survey planning. In 2021, in the middle of COVID-19 delays and distancing requirements, the team began upgrades to their existing facilities and construction of a brand new telescope to kick off the latest survey, SDSS-V.

The Next Generation

In a wide-ranging publication that references not only astronomy research articles but also Plato, the Bhagavad Gita, an Egyptian tomb, and Tolstoy, the large collaboration describes that this latest survey is divided into three parts: the Milky Way Mapper, the Black Hole Mapper, and the Local Volume Mapper. The preexisting telescopes, which are outfitted with hundreds of tiny robots that can swivel fiber optic cables into place to collect spectra of up to 500 objects at a time, will handle the first two of these “mappers.” A brand-new facility in Chile that’s specifically designed to map the structure of nearby gas will handle the last mapper. Instead of aiming the fibers at a known star or galaxy, this telescope will instead collect a spectrum for every point across an area the size of the full Moon with every exposure.

By the end of the survey, SDSS-V will have collected optical and near-infrared spectra for roughly 6 million objects spread across the whole sky, as well as time-series spectra from about a million of these sources. This dataset, which is unprecedented in both its spatial and temporal coverage, will allow researchers to probe questions ranging from how quasars evolve over time to how commonly young stars have brown-dwarf companions. Long since SDSS initiated the era of industrial survey astronomy, this latest publication shows how the survey continues to lead the way.

Citation

“Sloan Digital Sky Survey. V. Pioneering Panoptic Spectroscopy,” Juna A. Kollmeier et al 2026 AJ 171 52. doi:10.3847/1538-3881/ae0576

The post A New View of the Spectroscopic Universe appeared first on AAS Nova.

Nature sometimes behaves in ways that are difficult to recreate in simulations. New research tackles the computational challenge of turbulent mixing and rules out a commonly assumed source of data–model disagreement.

Mixing Up Stellar Interiors

What do Earth’s oceans, red giant stars, and white dwarfs have in common? These are all sites of thermohaline mixing, a form of turbulent mixing that takes place when there is a vertical gradient in both temperature and chemical composition. For example, in Earth’s oceans, water near the surface is warmer and saltier than water in the depths below, setting up an unstable situation prone to mixing.

Thermohaline mixing has been explored in simulations to explain the evolution of red giants’ surface abundances, as well as how quickly rocky debris that accretes onto a white dwarf is absorbed into the star. However, effectively modeling this process in the interiors of stars has proven difficult.

One of the most important parameters for modeling mixing is the Prandtl number, Pr, which is the ratio of viscosity to thermal diffusivity (in other words, a way of describing whether momentum or heat diffuses more quickly within a fluid). For stellar interiors, Pr is around 10⁻⁶, but computational limitations have prevented modelers from setting this value lower than around 10⁻². When tensions between models and reality arise, this gap between simulated and realistic Pr values is often assumed to be the source of the mismatch.

Bridging the Prandtl Number Gap

In a recent research article, Adrian Fraser (University of Colorado Boulder) aimed to test this assumption. Fraser carried out 3D simulations of thermohaline mixing, using a semi-implicit modeling technique that lowered the computational cost and allowed the simulations to probe Pr values of 10⁻¹, 10⁻², 10⁻³, 10⁻⁶, and 0.

By comparing these results against a benchmark model of thermohaline mixing, this exploration showed that adopting a realistic value of Pr doesn’t dramatically change the dynamics of the system — meaning that data–model incompatibilities can’t be swept under a Prandtl number–shaped rug and must instead be resolved by including additional physics.

Recreating Reality

Where does this leave modelers attempting to recreate the reality of stellar interiors? First, a silver lining of this investigation: Fraser found that setting Pr = 0 delivered nearly identical results to Pr = 10⁻⁶. This suggests that valid results can be attained in a much less computationally intensive way, since setting Pr = 0 lowers the complexity of the simulation. While simulations with Pr = 0 may not be appropriate for all scenarios, including systems with strong magnetic fields, it may provide a way forward in certain situations.

For modeling of red giants and white dwarfs, Fraser suggested that incorporating magnetic fields, stellar rotation, or additional sources of mixing may resolve the current discrepancies. In fact, some modeling work has shown that magnetic fields could entirely close the gap between observations and models for red giant surface abundances — suggesting that bringing models and observations into agreement may be within reach.

Citation

“Bridging the Prandtl Number Gap: 3D Simulations of Thermohaline Convection in Astrophysical Regimes,” Adrian E. Fraser 2026 ApJL 1001 L22. doi:10.3847/2041-8213/ae5796

The post Simulations of Turbulent Mixing Close One Gap but Open Another appeared first on AAS Nova.

Galaxies pull in and pump out gas as they form and evolve, but distinguishing between the two directions is tricky. A recent study used emission lines and dust absorption to try to pin it down.

Inflow or Outflow?

Throughout their lives, galaxies churn gas into stars, stars fuse new metals, supernovae blow enriched material back out, and the cycle repeats. To maintain this process and sustain star formation, a galaxy must fuel up by accreting gas from its surroundings. However, catching galactic gas accretion has proven difficult — both emission from gas falling into the galaxy (inflows) and gas blown out by supernovae (outflows) can appear blueshifted or redshifted along an observer’s sight line, depending on if the flowing material is in front of or behind the galaxy.

While direct evidence of inflows has been identified in the Milky Way, only a few direct detections of inflowing gas in other galaxies exist due to the degeneracy of inflow and outflow emission-line features. Relying on additional absorption measurements, some studies have teased out inflows in other galaxies, but these star formation fuel pumps remain overwhelmingly evasive. The angle at which we observe a galaxy also limits our ability to detect both inflows and outflows, with face-on galaxies best oriented to detect these shifted spectral features. How then do we uncover this critical component of a galaxy’s evolution?

Breaking Through with the Balmer Decrement

To try to break through the confusion between inflows and outflows, Meghna Sitaram (Columbia University) and collaborators explored how the strengths of hydrogen emission lines vary depending on the location of the emitting gas. Referred to as the Balmer decrement, the ratio between the Hα (redder) and Hꞵ (bluer) emission lines is sensitive to dust between the emitting gas and the observer. Because dust preferentially absorbs bluer photons, an inflow or outflow behind a galaxy is expected to have a higher Hα/Hꞵ ratio due to the intervening dust in the galaxy’s disk absorbing some of the Hꞵ emission.

Testing this idea, the authors performed a hydrodynamic simulation of an isolated, face-on Milky Way–like galaxy and tracked inflows and outflows over a billion years. From the simulation, they extracted mock spectral observations to measure the ionized gas motions and Hα and Hꞵ emission lines along different sight lines throughout the galaxy. Separating gas components into three categories — inflow, outflow, and in the disk — the authors found that dust extinction does cause noticeable differences in the Balmer decrement depending on a component’s location with respect to the disk.

Front Inflow Finds

What does this mean for identifying the inflows that provide galaxies with star-forming fuel? The authors reported that components in front of the galaxy — redshifted inflows and blueshifted outflows — tend to exhibit lower Hα/Hꞵ ratios compared to components behind the disk, aligning with the expectation that dust in the disk absorbs Hꞵ. In particular, these front inflows appear to be the most readily distinguished from gas in and behind the galaxy’s disk.

However, things get more complicated for gas behind the galaxy. Because the dust in the simulation is distributed nonuniformly in small clumps throughout the galaxy, it is difficult to distinguish between disk gas and gas behind the galaxy. While future simulations with improved dust modeling are necessary to resolve this issue, this study offers a useful method to distinguish inflow and outflow in dusty face-on galaxies.

Citation

“Identifying Signatures of Inflow onto Face-On Galaxies Using Balmer Decrement,” Meghna Sitaram et al 2026 ApJ 1001 87. doi:10.3847/1538-4357/ae5222

The post In or Out? Using Balmer Emission to Distinguish Inflows from Outflows appeared first on AAS Nova.

In 2019, a supermassive black hole in a galaxy 300 million light-years away woke up. Now, it’s puzzling astronomers with an unexpected slowdown in its X-ray bursts.

Ansky Awakens

Nearly seven years ago, the Zwicky Transient Facility saw the galaxy SDSS J133519.91+072807.4 suddenly brighten at optical wavelengths, with the source given the moniker ZTF19acnskyy or “Ansky.” Within the next few years, Ansky brightened at other wavelengths, possibly signaling the first recorded case of a slumbering supermassive black hole grumbling to alertness.

In 2024, Ansky entered a new phase of behavior, exhibiting a series of semi-regular X-ray flares called quasi-periodic eruptions. The leading explanations for these flares, which have been detected from several nearby galaxies, involve a star-sized object spiraling toward a supermassive black hole. The repeating X-ray flares arise when the object crashes through an accretion disk around the black hole, or when the object loses mass each time it passes closest to the black hole. In either scenario, the time between flares is expected to decrease over time — but as new work shows, Ansky is behaving in ways that fail to fit existing theories of quasi-periodic eruptions.

An Unexpected Slowdown

Astronomers first reported on Ansky’s strange behavior in 2025, finding evidence that the time between eruptions was increasing rather than decreasing as expected. To investigate this emerging trend, Joheen Chakraborty (Massachusetts Institute of Technology) and collaborators analyzed data from the Neil Gehrels Swift Observatory’s X-ray Telescope, XMM-Newton, and the Neutron star Interior Composition Explorer (NICER).

This X-ray monitoring campaign spanned from January 2025 to January 2026 and captured 23 bursts, including 19 consecutive bursts — the most seen from a quasi-periodic eruption source to date. The bursts each lasted about three days, and the burst luminosity and total energy remained roughly constant, but the time between bursts increased smoothly from 9.9 days in January 2025 to 13.5 days in January 2026.

Possible Explanations

What physical process can produce X-ray bursts that are roughly consistent in energy and peak luminosity, last for approximately three days, and become more spaced out over time? The team considered five possibilities:

1. A star orbiting a black hole could transfer a bit of mass to the black hole each time it draws close… but it’s not clear whether the energy of each burst would remain the same as the star loses mass, nor is it clear how a three-day eruption duration could be achieved.
2. A star partially disrupted by a black hole could be kicked progressively farther from the black hole due to asymmetric mass loss or the reformation of its core… but this scenario cannot explain the bursts’ consistent energies and luminosities.
3. An object orbiting a black hole with an accretion disk could be experiencing general relativistic precession… but no combination of known sources of precession can reproduce Ansky’s behavior.
4. A second supermassive black hole could cause reflex motion of the inner black hole, changing how far the signal must travel… but even though this scenario can increase the time between bursts, the rate of increase is three orders of magnitude too small.
5. Instabilities in the black hole’s accretion disk could trigger recurrent bursts of accretion… but it’s not yet clear how an instability scenario could produce such predictable behavior.

While none of these models can fully solve the mystery of Ansky’s slackening X-ray flares, this work provides new avenues for exploration. In the meantime, we may get new clues simply from waiting to see what this source does next!

Citation

“A Positive Period Derivative in the Quasiperiodic Eruptions of ZTF19acnskyy,” Joheen Chakraborty et al 2026 ApJL 1001 L6. doi:10.3847/2041-8213/ae548b

The post A Black Hole’s Puzzling X-Ray Bursts appeared first on AAS Nova.

The Sun’s activity history, the sources of tiny jets, and how magnetic fields might impact space weather forecasts: today’s Monthly Roundup introduces a trio of recent research articles from the Astrophysical Journal that tackle hot topics in solar physics.

From 1755 to 2020: Reconstructing Centuries of Solar Activity

Since the 1970s, regular monitoring of the Sun’s magnetic field has allowed researchers to decipher the Sun’s behavior as it cycles through periods of low and high activity. But what resources exist for studying the Sun’s past behavior? To investigate the long-term behavior of the Sun, researchers reach for historical records of sunspots, which stretch back to the 1700s.

Bibhuti Kumar Jha (Southwest Research Institute) and collaborators explored whether historical records and modern statistics could be used to reconstruct the behavior of the solar magnetic field centuries into the past. Jha’s team used recorded sunspot numbers from 1755 to 2020 as an input for their newly developed Synthetic Active Region Generator, which generates synthetic solar active regions based on known statistics of these regions. This catalog of active regions becomes the input for the Advective Flux Transport model, which simulates the active regions as they emerge and evolve, allowing for an estimation of the magnetic field across the Sun’s disk.

Jha and coauthors found that this method successfully reproduced the expected large-scale behavior of the Sun’s magnetic field across multiple solar cycles, such as the reversal of the polarity of the solar magnetic field near the peak of the activity cycle. While this work highlights the impressive results obtained from combining historical sunspot records with modern sunspot statistics, the team pointed out that this method cannot accurately reproduce all quantities because of the nonlinear nature of the underlying physics. Future work will refine the model further, and in the meantime, the team’s simulated historical magnetic field maps will be made publicly available.

Where Do the Tiniest Coronal Jets Come From?

The Sun’s atmosphere is filled with an ever-shifting maze of magnetic field lines, which reconfigure and release pent-up magnetic energy in a process called magnetic reconnection. Magnetic reconnection can launch particles and heat plasma, and it’s thought to be responsible for driving jets on a variety of scales in the Sun’s tenuous outer atmosphere, or corona. Annu Bura (Indian Institute of Astrophysics; Pondicherry University) and coauthors investigated the physical origins of the smallest of these reconnection driven jets, picoflare jets, using data from the Extreme Ultraviolet Imager on board Solar Orbiter. Solar Orbiter has ventured within 0.3 au of the Sun, and its Extreme Ultraviolet Imager has returned exceptionally precise high-energy images of our home star.

Bura and collaborators identified picoflare jets by the presence of a hot, bright spire coupled with a cool, dark streak, forming a structure shaped like the letter “Y” upside down. They found that the bright and dark features were on average 650 and 490 kilometers wide, respectively, with a typical jet length of 16,900 kilometers. They also found that the bright features moved more quickly than the dark features, and the jets tended to last about 6 minutes. Overall, these measurements place the jets in between the scales expected for picoflare jets and slightly larger features called jetlets, though the energies are consistent with expectations for picoflare jets.

Using radiation magnetohydrodynamics simulations, the team explored the origins of their sample of jets. The simulations suggested that the bright features arose from hot, tenuous coronal plasma, while the accompanying dark features were due to cooler, denser plasma venturing upward from deeper in the Sun’s atmosphere, in the chromosphere. Overall, the simulations and observations support a picture in which picoflare-scale jets are driven by magnetic reconnection after magnetic flux emerges through the Sun’s surface. This echoes the formation route of larger coronal jets, suggesting that this process may apply to a wide range of physical scales.

Investigating the Influence of the Solar Polar Magnetic Field

The vast majority of our observations of the Sun have come from within a few degrees of the ecliptic plane, either from telescopes situated on Earth’s surface or from spacecraft that stuck close to the plane of our solar system. With rare but notable exceptions — the Ulysses spacecraft, which measured the Sun’s magnetic field and plasma environment from a near-polar orbit, and Solar Orbiter, which took the first-ever image of the Sun’s poles in November 2025 — the Sun’s poles have remained hidden from our instruments.

Our limited knowledge of the Sun’s polar magnetic field has consequences for our ability to model space weather events like coronal mass ejections. A team led by Xiao Zhang (Chinese Academy of Sciences; University of Chinese Academy of Sciences) has used numerical simulations to investigate how solar polar magnetic field conditions influence the propagation of a coronal mass ejection (CME) through the solar system.

The team simulated a CME from 4 December 2021, which was observed by the BepiColombo spacecraft at Mercury and Tianwen-1 and MAVEN at Mars. The simulations showed that as the polar magnetic field strength increases, the CME’s movement through the solar system becomes slower. CMEs typically expand as they billow outward from the solar corona and sweep past the planets; increasing the polar magnetic field strength slowed the CME’s expansion as well. A stronger polar magnetic field also alters the background solar wind, making it slower and denser. Overall, these results demonstrate that the strength of the Sun’s poorly constrained polar magnetic field can have a significant impact on the movement and evolution of a CME. In future work, Zhang’s team plans to expand their investigation to a larger sample of CMEs.

Citation

“Historical Reconstruction of Solar Surface Magnetism from Cycles 1–24 Using the Synthetic Active Region Generator and the Advective Flux Transport Model,” Bibhuti Kumar Jha et al 2026 ApJ 997 279. doi:10.3847/1538-4357/ae279a

“On the Origin of Coronal Picoflare Jets,” Annu Bura et al 2026 ApJ 1000 94. doi:10.3847/1538-4357/ae48e6

“Influence of Solar Polar Magnetic Fields on the Propagation of Coronal Mass Ejections,” Xiao Zhang et al 2026 ApJ 1000 200. doi:10.3847/1538-4357/ae4c54

The post Monthly Roundup: Science of the Sun appeared first on AAS Nova.

How do galaxies grow? A massive survey from JWST can help astronomers answer that fundamental question about galaxy evolution.

Time Machines

When astronomers look into the night, they are greeted by a sky full to bursting with galaxies. But immediately after the Big Bang, none of these grand structures could have existed in our universe: all of the matter was too hot and dense to collapse into the whirlpools and ellipses we see today. We know that it took time for dark matter to collapse into halos, for gas to cool and fall into those halos, and even more time for those halos to merge together and galaxies to form. However, quantifying that story is tricky. How long did it take for the gas to cool and collapse? How often did small galaxies merge? How did the birth and death of stars play into all of this?

One way astronomers could go about answering these deep, fundamental questions in galaxy evolution would be to look at many galaxies spread across different distances. Famously, since the speed of light is fairly slow (cosmically speaking), we can only see distant objects as they appeared in the past. (This is why any aliens looking toward Earth from 65 million light-years away — from within the Virgo Cluster, perhaps — would see our planet as it was when dinosaurs roamed free.) In principle, then, by looking at a progression of galaxies farther and farther away, astronomers could convert these still images into a sort of movie of how typical galaxies look moving further and further back in time.

Seeing Red

There is a complication to this strategy, however. The farther away an object is, the more the light it emits is stretched towards redder wavelengths. As a consequence, any telescope designed to detect visible light won’t see anything; to take pictures of these galaxies, we need to build detectors that are specifically sensitive to stretched-out, near-infrared light.

This is one of the primary reasons that JWST was designed, constructed, and flung into space. It was purpose-built to collect and analyze near-infrared light from distant galaxies, and now after several years of observations and data crunching, astronomers are finally getting some answers to those fundamental questions.

A Massive Survey

Recently, a team led by Lilan Yang, Rochester Institute of Technology, released their analysis of one of the earliest and largest surveys JWST has undertaken, a program called COSMOS-Web. The researchers mined a patch of sky about the size of the full Moon and extracted more than 30,000 distant galaxies, most of which had never before been seen by human eyes. They measured the brightness and size of each one and grouped them according to their redshift (a proxy for their distance) and whether they were actively forming stars or not.

The team found that, unsurprisingly, galaxies tend to grow over time. Excitingly, however, they also found that for star-forming galaxies, the relationship between a galaxy’s mass and its size is fairly constant for redshifts of z = 2–8. The scaling law between them also nicely matches up with measurements taken by the Hubble Space Telescope at smaller redshifts. Beyond that, though, for redshifts of z = 8–10, it’s possible that the scaling changes, though the authors emphasize that their sample is much smaller in these distant bins.

While more data are needed to confirm whether the youngest of these galaxies grow at a different pace than their later counterparts, we can be comforted that studies like this represent just our very first peek into a whole new era of galactic evolution, and that many more insights are sure to come as JWST keeps snapping images.

Editor’s Note: This article previously contained an error relating to the distance at which aliens would see Earth as it was when inhabited by dinosaurs. This error was corrected on 4 May 2026.

Citation

“COSMOS-Web: Unraveling the Evolution of Galaxy Size and Related Properties at 2 < z < 10,” Lilan Yang et al 2025 ApJS 281 68. doi:10.3847/1538-4365/ae0e1b

The post How Galaxies Grow Up appeared first on AAS Nova.

What factors impact how long it takes for a supermassive black hole binary to merge? New research investigates the influence of orbital inclination on the population of merging black holes in our universe.

One Merger Leads to Another

When galaxies merge, the supermassive black holes at their centers are thought to link up in a binary system and eventually merge as well. Evidence for these supermassive black hole pairs and their collisions is piling up: researchers have identified a small but growing number of galaxies containing two accreting supermassive black holes, and the compelling evidence for the gravitational wave background points to the existence of an immense population of supermassive black hole binaries.

With observational evidence for supermassive black hole mergers taking shape, theorists are exploring the details of these mergers. One aspect of this process that hasn’t yet been examined fully is how the relative inclination of the merging galaxies impacts the time it takes for their central black holes to merge — a factor that has the potential to shape the demographics of merging supermassive black holes across our universe.

Ready, Set, Spiral

Sena Ghobadi (Georgia Institute of Technology) and collaborators used 3D dynamical models to explore how the angle at which galaxies collide — and therefore how the black holes’ orbits are tilted relative to one another — impacts the time it takes the supermassive black holes at their centers to merge.

In the simulations, Ghobadi’s team placed a 10⁶–10⁸-solar-mass black hole at the center of a disk galaxy. Then, they sent a second, smaller black hole spiraling toward it from a distance of 1 kiloparsec (3,300 light-years).

The team varied the inclination of the incoming black hole’s orbit relative to the disk of the target galaxy from 0 to 75 degrees. They also explored the impact of changing the black hole masses and the galaxy’s central gas density, disk rotation speed, and gas mass fraction. For each simulation, they recorded how long it took for the incoming smaller black hole to get within 10 parsecs of the larger black hole.

(Dis)inclined to Merge

The simulations showed a clear trend with changing inclination: a black hole with an orbital inclination greater than 20 degrees took longer to merge than those with inclinations of 0–20 degrees. For black holes approaching the merger on slightly inclined orbits, dynamical friction between the black hole and the stars and gas of the galaxy worked to drag the black hole down into the disk, decreasing its inclination over time and guiding it toward a merger. Aside from the influence of inclination, the team also found that higher-mass supermassive black holes and more rapidly rotating galactic disks tended to lead to faster mergers.

For inclinations greater than roughly 45 degrees, a dramatic transition took place, with the orbits of the incoming black holes becoming more inclined over time rather than settling down into the disk. These simulated black holes failed to merge in the allotted time of 14 billion years.

With highly inclined binaries failing to merge within the lifetime of the universe, this suggests that the dual active galactic nuclei and the supermassive black hole binaries that produce gravitational waves in the universe today are the result of binaries with initial inclinations of 20 degrees or less.

Citation

“Evolution of Supermassive Black Hole Pairs on Inclined Orbits in Postmerger Galaxies,” Sena Ghobadi et al 2026 ApJ 999 131. doi:10.3847/1538-4357/ae40bc

The post How Tilted Orbits Impact Supermassive Black Hole Collisions appeared first on AAS Nova.

Prior to exploding, massive stars advance through action-packed evolutionary stages that are exciting but often difficult to fully decipher. A recent study focuses on a unique late-stage star to better understand its properties and evolution.

To B[e] a Supergiant

After depleting their cores of hydrogen, massive stars journey off the main sequence through a series of evolutionary phases before ending in dramatic supernova explosions. A massive star’s post-main-sequence evolution is intense, often sloughing off layers of material that can settle into a circumstellar disk. The B[e] supergiant phase describes a blue supergiant star surrounded by a cool, dense circumstellar disk where oxygen is more abundant than carbon. These environments often lock up carbon atoms in carbon monoxide molecules, leaving excess oxygen available to form other molecules including SiO, TiO, and water vapor. These molecules can survive under different physical conditions, making them key tracers of the environments around B[e] supergiants.

One particularly interesting B[e] supergiant, LHA 115-S 18, has been the subject of numerous studies but remains poorly constrained. The star exhibits significant variability both in brightness and emission features on timescales of days to years, and previous works have suggested that the star may have an as-yet unconfirmed binary companion. Molecular line emission from CO and TiO have been identified in LHA 115-S 18, indicating a circumstellar disk, but to date, water vapor emission has not been identified in any B[e] supergiant. Identifying more complex oxygen-bearing molecules like water will further reveal the physical properties and possible binary companion of LHA 115-S 18.

Identifying Emission in LHA 115-S 18

To characterize the emission around LHA 115-S 18, María Laura Arias (Institute of Astrophysics La Plata; National University of La Plata) and collaborators obtained high-resolution near-infrared spectroscopy of the star using the Immersion Grating Infrared Spectrometer on the Gemini South telescope. From the high-resolution spectra, the team identified several atomic emission lines indicative of the star’s gaseous envelope, revealing the structure of material around the star: an inner hot disk of ionized material and an outer cool disk of neutral material. Looking at molecular emission from carbon monoxide — a tracer of both gas motions and stellar age — the authors confirmed the presence of a rotating ring of gas around LHA 115-S 18 and determined that the star is an evolved, post–red supergiant object.

Through computing a synthetic spectrum to compare to the observed spectrum, the authors identified many water vapor emission lines in the circumstellar environment around LHA 115-S 18. While water vapor has been detected in other evolved late-type stars, this is the first detection of water vapor from a B[e] supergiant star. For water vapor to survive the star’s intense radiation, it must exist in a dense, cool, heavily shielded disk around the B[e] supergiant.

Sustaining a cool disk around such a hot star indicates that the circumstellar environment around LHA 115-S 18 is complex and likely shaped by binary interaction. With emission features characteristic of both cool and hot evolved stars, this particular B[e] supergiant presents itself as a unique object holding critical insights into the late-stage evolution of massive stars. Further multiwavelength observations of LHA 115-S 18 will constrain its potential binarity and reveal a possible evolutionary link between B[e] supergiants and other late-stage evolutionary phases of massive stars.

Citation

“High-resolution Near-Infrared Spectroscopy of the B[e] Supergiant LHA 115-S 18: Discovery of Hot Water Vapor Emission,” María Laura Arias et al 2026 ApJL 1000 L49. doi:10.3847/2041-8213/ae524a

The post Water Vapor Around a Sizzling Supergiant: High-Resolution Spectroscopy of B[e] Supergiant LHA 115-S 18 appeared first on AAS Nova.

The Event Horizon Telescope (EHT), the facility that delivered humanity’s first-ever picture of a black hole, can produce some of the sharpest images in all of astronomy. But turning the EHT’s raw data into images is a complex process involving messy statistics and powerful algorithms. Recent work presents a potential upgrade to that process: for the first time in long-baseline interferometry, it may be possible to model everything everywhere all at once.

The Hardest Eye Test

The EHT has some of the sharpest eyes in all of astronomy. With its effective resolution of just 20 microarcseconds, in principle you could use it to read a newspaper in New York while sitting at a cafe in Paris. But this planet-spanning instrument (it relies on data from radio telescopes on four continents) doesn’t snap pictures like an ordinary camera. Instead, each pair of telescopes measures something called an “interferometric visibility,” which is related to a single Fourier component of the actual underlying image.

Combining these components into an image is a process fraught with assumptions and modeling choices. Since the EHT doesn’t have an infinite number of telescopes, each measurement can be mapped to infinitely many images. This forces researchers to choose how to “regularize” this space of images to select one best picture. Making things harder, they also must contend with all the typical issues of real-world data collection. Each telescope has slight calibration errors, and every data point is affected by weather and temperature-dependent processes.

Typically researchers break the problem down into several stages: first calibrate the data, then regularize and construct the best-fitting image, then analyze that image to constrain the actual physics you care about like the width of the ring surrounding a black hole. This is how the original EHT publications went about their groundbreaking work on the now-iconic glowing ring around the supermassive black hole in the galaxy Messier 87 (M87*).

A New Approach

Recent work led by Paul Tiede (Black Hole Initiative at Harvard University) suggests an alternative process. Instead of separating the stages of analysis as described above, the team demonstrated that one could fit everything simultaneously in a framework they call hierarchical interferometric Bayesian imaging, or HIBI.

By fitting all parameters that go into an image together, the method doesn’t select one “best” image. Instead, by allowing the pixel-by-pixel intensities, calibration parameters, and underlying physics to inform one another during inference, HIBI explores the full range of images consistent with the data. This prevents the degeneracies that plague the traditional approach, where image and calibration estimates can trade off against each other in misleading ways. The team validated HIBI on synthetic data mimicking the EHT’s 2017 setup, showing that it reliably recovered a range of source shapes with well-calibrated uncertainty estimates.

Even more exciting, the team demonstrated that it’s possible to skip the image construction step altogether and go straight to the science. By fitting parameters describing the physics underlying a scene, the team was able to constrain the width of the ring around M87* without any reference to a picture. They predict that this technique could be crucial for extracting information when future instruments like the Next Generation Event Horizon Telescope observe more distant black holes that are only marginally resolved. Though we’ll likely have to wait years for these next-generation telescopes, work like this ensures that astronomers will be able to squeeze as much science from them as possible once these new facilities are ready.

Citation

“Hierarchical Interferometric Bayesian Imaging,” Paul Tiede et al 2026 ApJ 997 262. doi:10.3847/1538-4357/ae2749

The post Enhancing the Sharpest Images appeared first on AAS Nova.

Researchers tracked the tail of comet C/2023 P1 (Nishimura) as it interacted with a string of coronal mass ejections, leading to the first-ever quantitative analysis of a cometary tail detachment event.

A Comet’s Journey

When comets journey into the inner solar system, they tend to do so sporting two tails: a dust tail that sweeps back from the comet along its curved trajectory and an ion tail that points away from the Sun, in the direction of the interplanetary magnetic field.

The ion tail, which forms when ultraviolet light from the Sun ionizes gas in a comet’s fuzzy coma, interacts with structures in the solar wind, causing it to shift, sputter, and sometimes even disconnect entirely. Now, for the first time, researchers have quantified the timescales involved when a comet loses — and regrows — its tail.

The Tale of a Tail

Shaheda Begum Shaik (George Mason University; US Naval Research Laboratory) and collaborators studied this phenomenon in observations of the comet C/2023 P1 (Nishimura) from 1 to 14 September 2023. In high-resolution images from the Solar Orbiter Heliospheric Imager, Shaik’s team analyzed the dynamics of C/2023 P1’s tail as the comet braved blustery solar wind conditions in the inner solar system.

In a two-week period, the comet underwent four separate tail disconnection events, in which the connection between the ion tail and the comet was severed. Each of these events coincided with the passage of a coronal mass ejection: a tangled mass of solar plasma and magnetic fields ejected from the Sun’s outer atmosphere.

Lizard-Like Regrowth

Focusing on the tail disconnection event with the highest-resolution and highest-cadence data, Shaik’s team observed constant small-scale fluttering of the ion tail, reflecting the buffeting of the tail by the solar wind. The tail then developed a kink, which the team speculated is due to compressed solar wind plasma piling up in front of an oncoming coronal mass ejection. The wide-field images show the coronal mass ejection advancing upon the comet and the comet’s tail seemingly being sliced in two.

The free-floating tail segment sped away from the comet at roughly 295 km/s, likely indicating that the tail became caught up in and was transported by the flank of the coronal mass ejection as it barreled past the comet. The timescale and geometry of the event suggest that the interaction of the coronal mass ejection’s magnetic field with the comet’s tail was responsible for the disconnection.

Over the following 24 hours, the comet’s tail slowly regrew at a rate of 86 km/s to its original length of 1.9 million kilometers. The rate of regrowth is likely determined by several factors, such as the rate at which the comet produces ions and the local magnetic field configuration. This work represents a first look at the quantitative behavior of a tail disconnection event, paving the way for future investigations of cometary behavior and a greater understanding of the complex magnetic and plasma environment of the inner solar system.

Citation

“The First Quantitative Study of Cometary Tail Regrowth Following a Coronal Mass Ejection-Driven Disconnection Event,” Shaheda Begum Shaik et al 2026 ApJ 999 60. doi:10.3847/1538-4357/ae3bdb

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