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 (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.
The full exoALMA sample. All 15 disks show evidence of substructure in their gas emission. [Teague et al. 2025]
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
In the model explored by Jim Fuller and collaborators, repeated mass-ejection events can cause red giant stars to be “kicked” up to a relatively high velocity before they collapse to form white dwarfs, explaining the high velocities many white dwarfs are observed to have. [Jim Fuller]
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
Multiwavelength images of two nearby quasars show that the hot X-ray (red) and warm ionized (green) gas are far more extended in the bottom system. Click to enlarge. [Anna Trindade Falcao]
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.
The three types of wind launched from an accreting supermassive black hole. Click to enlarge. [Xin Xiang]
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:
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- 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.
- 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.
- 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.
- 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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