Editor’s Note: This week we’re at the 248th AAS meeting in Pasadena, CA. Along with a team of authors from Astrobites, we will be writing updates on selected events at the meeting and posting each day. Follow along here or at astrobites.com for daily summaries, or follow @astrobites.bsky.social on Bluesky for more coverage. The usual posting schedule for AAS Nova will resume on 22 June.
Table of Contents:
- Plenary Lecture: Eliza Kempton, Common Worlds, Uncommon Complexity: Sub-Neptune and Super-Earth Atmospheres in the JWST Era
- Press Conference: Stars Reshaping Galaxies: Clusters, Feedback, and Explosive Aftermaths
- Plenary Lecture: George Helou, The Cosmic Infrared Window: Photons, Technology, and People
- Plenary Lecture: Carolyn Kuranz, Creating Astrophysical Conditions at High Energy Density Facilities
- Plenary Lecture: Cara Battersby, Our Galaxy’s Dynamic Center
Plenary Lecture: Eliza Kempton, Common Worlds, Uncommon Complexity: Sub-Neptune and Super-Earth Atmospheres in the JWST Era (by Lexi Gault)
Eliza Kempton began her talk addressing the undergraduates in the room, showing the meeting website from AAS 200, which she attended as an undergraduate in 2002. Searching this page, there were no presentations on exoplanets — a stark difference from the boom of exoplanet science that we see 24 years later at AAS 248, marking how significantly a field can transform from the start of your career.
Situating us outside of the solar system, Kempton showed the quintessential mass–period plot of all 6,000+ detected exoplanets thus far. Strikingly, we have discovered new types of planets that are not seen in our own solar system, but uncovering exoplanet populations is heavily skewed due to detection limits. While it is much easier to find large planets closely orbiting their stars, occurrence rate studies have shown that small planets on close-in orbits are much more common and typically come in two sizes: gas-rich sub-Neptunes and rocky super-Earths. However, actually deciphering their compositions relies on detailed studies of their atmospheres, which is the primary research work Kempton dove into.
How do we study exoplanet atmospheres? Thankfully, JWST provides the wavelength range and collecting area necessary for observing the minute details in exoplanet atmospheres. Beginning with sub-Neptunes, Kempton laid out four important takeaways from recent work coming from her team:
- Sub-Neptune atmospheres composed of heavier elements and molecules are common.
- Clouds and hazes are pervasive for planets that get a moderate amount of light from their host star. Early JWST observations showed signatures that may point to soot formation in sub-Neptune inner atmospheres; this soot can rise, making the upper atmosphere we observe hazy.
- Sub-Neptune atmospheres may provide a window into their interiors. Observed atmosphere compositions may indicate no solid planetary surface, but rather magma, water, and/or gas that can mix more readily with the upper atmosphere.
- Tying atmospheric observations to formation scenarios is still a challenge. Constraints on planets’ bulk composition has not provided clear answers.
Moving down to super-Earths, Kempton introduced the idea of the cosmic shoreline — the empirical relationship between planetary escape velocity and stellar irradiation shows a stark dividing line between planets with and without atmospheres in our solar system. Does this concept of a cosmic shoreline exist for exoplanets? Kempton highlighted three takeaways for the study of super-Earth atmospheres:
- Spectroscopy of super-Earth atmospheres presents degeneracies in determining their characteristics. A featureless spectrum could be due to the presence of heavy molecules and clouds, or it could just mean the planet has no atmosphere.
- Thermal emission is a powerful tool for identifying candidate atmospheres. The eclipse depth of a transiting planet is directly related to the day-side temperature of the planet. Planets with and without atmospheres will have different day-side temperatures — hotter without an atmosphere, cooler with an atmosphere.
- Many (but not all) transiting super-Earths are bare rocks.
Clearly, JWST has allowed astronomers to make significant progress in understanding exoplanet composition and subsequently their possible formation and evolutionary histories. Kempton ended with reminding us where we came from 24 years ago — the field of exoplanet science has boomed, and we can wonder how much we’ll continue to uncover in the next 24 years.
Press Conference: Stars Reshaping Galaxies: Clusters, Feedback, and Explosive Aftermaths (Briefing video) (by Niloofar Sharei)
This press conference brought together four very different views of star-forming environments: the most distant galaxy cluster caught strongly lensing a background galaxy, the dense young star clusters tucked inside the rings of nearby galaxies, the extreme feedback physics inside the closest luminous infrared galaxy merger, and the first known pair of supernova remnants born from a binary star system.
A New Era of Galaxy Cluster Analysis at Cosmic Noon: JWST’s View of a Distant Galaxy Cluster
Kyle Finner (IPAC/Caltech), presented the discovery of strong gravitational lensing in XLSSC 122, the most distant known galaxy cluster, seen as it was about 10.3 billion years ago. When the team got their JWST imaging back, they noticed bright blue arcs around the brightest cluster galaxy, a clear signature of strong lensing from a background galaxy sitting in just the right place behind the cluster. Using those arcs, the team measured the radial dark matter profile and found that XLSSC 122 is much more centrally concentrated than cosmological simulations predict. To check whether the cluster itself is unusual, they combined the JWST result with multiwavelength data. All of those tracers show an elongated structure pointing the same way as the dark matter, which is a strong sign that XLSSC 122 is a merging cluster. But mergers usually lower concentration rather than boost it, so the question of why this early cluster looks so concentrated is still open. The team plans to follow up with more strong-lensing measurements. | Press release
This two-panel image shows a distant galaxy cluster as it has been observed by NASA’s Hubble Space Telescope and JWST. [NASA, ESA, CSA; Kyle Finner (Caltech/IPAC) Image processing: Robert Hurt (Caltech/IPAC-SELab)]
Sajia Shahrin Neha (University of Kentucky) presented a study of young massive clusters in the circumnuclear rings of two nearby galaxies: NGC 3351, a normal spiral, and NGC 1097, which hosts an active galactic nucleus. Young massive clusters are extreme star-forming systems that pack hundreds of thousands to millions of stars into a small region, and the ring-shaped star-forming zones around these galactic nuclei provide exactly the kind of dense gas and dust reservoir these clusters need. Because the clusters are heavily obscured, optical, ultraviolet, and infrared light cannot pass through cleanly, so Neha and collaborators turned to radio continuum imaging with the Atacama Large Millimeter/submillimeter Array and the Very Large Array, which can see through the dust. Their team identified 53 young massive cluster sources across the two rings. They also placed them on an evolutionary sequence: heavily embedded “starless” clumps, newborn clusters that are just starting to become visible, and older “exposed” clusters that have already burned through much of their gas. All evolutionary stages are present in both galaxies, regardless of whether the host has an active nucleus. | NRAO press release | U. Kentucky press release
Dusty and Over-Pressured: Measuring Stellar Feedback in the Closest Luminous Infrared Galaxy
Deb/Debosmita Pathak (The Ohio State University/IPAC) presented new measurements of pre-supernova stellar feedback in NGC 3256, the closest luminous infrared galaxy and a merger between two roughly Milky Way–mass galaxies. NGC 3256 forms stars about 60 times faster than the Milky Way, which makes it a useful nearby laboratory for the intense, clumpy star formation that dominated the early universe. Using JWST plus multiwavelength data, the team measured feedback pressures around roughly 1,700 young star clusters and compared them with what we see in quieter, normal star-forming galaxies. The results break the standard picture in two ways. First, the feedback and interstellar medium pressures in NGC 3256 are about a hundred times higher than what is typical in normal star-forming galaxies. Second, the dominant feedback mode is different: instead of warm ionized gas pressure doing most of the work, ultraviolet and infrared radiation pressure on dust dominates in these much dustier environments. Even at these much higher pressures, most clusters are still over pressured relative to their surroundings, meaning radiation is strong enough to drive expansion against a dense ambient interstellar medium. | NRAO press release | OSU press release
Unveiling the First Binary-System Supernovae
Miltiadis Michailidis (Kavli Institute for Particle Astrophysics and Cosmology (KIPAC)/Stanford University/SLAC National Accelerator Laboratory) closed the session with the discovery of what appears to be the first known supernova remnant pair born from a binary star system. The starting point is IC 443, one of the best-studied supernova remnants and one of the brightest gamma-ray sources in the sky, thanks to its interaction with a dense nearby molecular cloud. Recent eROSITA observations showed that the faint X-ray “shell” long noticed next to IC 443 is in fact a second, overlapping supernova remnant. The question was whether the two are physically related or just a chance alignment on the sky. They used 15 years of Fermi gamma-ray data and modeled and subtracted IC 443’s contribution and uncovered a distinct, hidden gamma-ray source associated with the new remnant.
The gamma-ray emission is strongly spatially segregated: its northern boundary, where it overlaps the same molecular cloud that IC 443 illuminates, is dominated by accelerated protons colliding with dense gas, while its southern boundary is dominated by accelerated electrons. The team also showed that the optical filament along the northern boundary is a radiative shock that has cooled past the point of efficient particle acceleration. Combined with the fact that both remnants sit at the same distance (about 6,000 light-years), and that a population-synthesis run with a million massive binaries reproduces the observed separation and age difference, the team argues that the two remnants are the remains of a true binary pair. | Press release
Plenary Lecture: George Helou, The Cosmic Infrared Window: Photons, Technology, and People (by Kerry Hensley)
George Helou (Caltech) gave a sweeping overview of infrared astronomy over the past 40 years, including the impressive role of the Infrared Analysis and Processing Center, or IPAC, which is celebrating its 40th anniversary.
The infrared portion of the electromagnetic spectrum is broad, encompassing wavelengths from 1 to 1,000 microns. In that wavelength range, there’s a lot going on in our universe: redshifted emission from distant galaxies, stars revealed by the drop in dust extinction, rotational and fine structure lines, molecular transitions, and fully half of the radiation density in the universe.
An example of how infrared capabilities have improved over time. [NASA/JPL-Caltech; MIRI: NASA/ESA/CSA/STScI]
Helou introduced a few science areas in which infrared missions have contributed greatly. First was the study of polycyclic aromatic hydrocarbons (PAHs), which are a class of molecules containing interconnected rings of carbon atoms. Thanks to infrared instruments, astronomers showed that various unassigned spectral features arose due to PAHs and that these molecules were important for the heating and cooling of the interstellar medium. As infrared instruments became more capable, observations showed how the fraction of carbon that is locked up in PAHs changes with metallicity and revealed novel species like deuterated hydrocarbon nanoparticles.
In the field of exoplanets, IRAS found evidence of excess infrared emission around Vega, hinting at a disk of debris that was later confirmed. (IPAC was instrumental in this discovery; the star Vega was being used for calibration, and the calibration wouldn’t converge because of the unexpected infrared excess.) Later, ISO used spectroscopy to investigate stellar debris disks and showed that they were similar in properties to solar system comets. Though Spitzer wasn’t initially expected to be used for exoplanet studies, the telescope made the first detection of photons from the surface of a planet and helped to discover several planets in the TRAPPIST-1 system. (Here, IPAC played an integral role again; instrument teams and flight engineers worked to ready the spacecraft for exoplanet observations by modifying the heaters on the spacecraft for pointing stability and finding “sweet spots” for photometric stability.) Today, JWST continues to advance the field with sensitive measurements of exoplanet atmospheres.
Finally, Helou touched on the work that IPAC has done to archive data. IPAC maintains the NASA/IPAC Extragalactic Database, or NED, which receives at least three queries per second. It’s also responsible for the Infrared Science Archive, data from which is used in more than 50% of research articles. IPAC also manages the NASA Exoplanet Archive, showing that the center isn’t limited to infrared astronomy!
As for the future of IPAC and infrared astronomy, it’s clear that there is much left to explore and lots of exciting work to be done; the Roman Space Telescope is scheduled to launch in a few months, and within a few years the Near-Earth Object Surveyor will follow. The Ultraviolet Explorer, for which IPAC will provide the UVEX Science Data Center, is slated to launch in 2030, and the PRobe far-Infrared Mission for Astrophysics (PRIMA) is under final review.
Read Astrobites’s interview with George Helou.
Plenary Lecture: Carolyn Kuranz, Creating Astrophysical Conditions at High Energy Density Facilities (by Lucas Brown)
While astronomy and astrophysics are often considered primarily observational sciences, with most targets of interest being millions to trillions of miles away from us — Carolyn Kuranz’s plenary talk helped to challenge this idea, demonstrating how we can sometimes bring the heavens down to Earth with high energy density (HED) facilities. The basic idea behind Kuranz’s work, and the field of HED laboratory astrophysics more broadly, is that some extreme astrophysical environments, particularly plasmas, can indeed be studied in the lab by producing smaller-scale analogs — so long as we choose the right types of experiments.
Kuranz structured her talk around three big questions she commonly gets asked about her field: firstly, why would astronomers want to do laboratory experiments? Then, what defines the “high energy density” in HED astrophysics? And finally, how do we actually do these experiments in practice? Starting with the why, Kuranz notes that studying systems in astrophysics is inherently difficult as a result of the fact that they are far away, and theoretical models can suffer from a lack of data or missing physics. Experiments can bridge the gap here, providing the ability to collect more data on specific systems of interest, complementing both theoretical models and observations.
While this philosophy can apply to a variety of laboratory astrophysics areas, such as laboratory-based studies of the chemistry of planetary atmospheres, Kuranz focused specifically on the emerging role of HED laboratory astrophysics. Typically, high energy density refers to systems with more than 1 million atmospheres of pressure and temperatures above 1 million K. Generally, this means we’re in plasma territory. In some ways, it’s only natural that studies of these sorts of environments would eventually help astrophysicists, given that around 99.9% of the matter in the universe is in plasma form. Despite this, the laboratory astrophysics side of HED physics has really only emerged over the past 30 years, with its origins being traced to work out of Lawrence Livermore National Lab, the current site of the National Ignition Facility (NIF).
Today, the NIF is only one of a few dozen facilities in which HED laboratory astrophysics experiments are conducted. This is because the type of equipment needed to reproduce environments analogous to various astrophysical systems can vary greatly. This gets to Kuranz’s third question of how these experiments are conducted. The process begins by answering a set of questions, including: do the astrophysical and proposed laboratory environments obey the same governing equations (conservation of mass, momentum, etc.)? Is one able to re-scale the physical parameters in each system (timescale, size, density, pressure, etc.) in a way that retains relevant dynamics like viscosity, Reynolds number, and so on? Once these details have been nailed down, a researcher can assess what types of facilities they may need. For example, the NIF, which uses symmetrical arrangements of lasers to compress and heat up millimeter-scale pellets containing gases that can undergo nuclear fusion, provides a fairly natural environment for studying processes in the cores of stars, which are also hot, dense, and neutron-rich environments where fusion is actively occurring.
As for the future, things look promising for HED laboratory astrophysics — since the NIF achieved “ignition” in 2022, producing a net gain of energy from one of these pellet-crushings for the first time, a huge amount of interest and investment has been flowing into facilities studying HED physics. These facilities range from private companies working to achieve sustained nuclear fusion power generation to longstanding federal research centers working on understanding nuclear weapons and stockpile management, but they all provide astronomers with the opportunity to do what was once unthinkable: bring the universe’s most extreme environments down to Earth.
Plenary Lecture: Cara Battersby, Our Galaxy’s Dynamic Center (by Niloofar Sharei)
Cara Battersby (University of Connecticut) used her plenary to walk us through her group’s ongoing effort to understand one of the most extreme environments in our own galaxy: the central molecular zone (CMZ), which is a dense, turbulent gas reservoir at the heart of the Milky Way. Her talk pulled together large surveys, new high-resolution zoom simulations, and machine-learning methods designed to bridge between the two.
She opened with the PRobe far-Infrared Mission for Astrophysics (PRIMA), the far-infrared probe mission concept she is a co-investigator on. This mission concept was developed in response to NASA’s recent billion-dollar probe mission call, and selection is expected later this year. PRIMA covers roughly 1.8–25 microns with imaging and spectroscopy, and galactic ecosystems make up about a quarter of its science case.
Battersby paused mid-talk to speak directly to early-career people in the audience about work-life balance, including bringing her daughter and sister with her to the meeting, and the SPARK program at UConn that supports women and underrepresented groups in physics. Her message: astronomy should be done from a place of joy, and visible work-life balance is something the community should be more open about.
Battersby framed the Milky Way as the natural laboratory for star formation across a huge range of environments, and briefly reviewed the ALMAGAL survey, which observed roughly 1,000 high-mass star-forming regions across the disk. But her main focus was the CMZ, which she argued is essentially a different kind of galaxy embedded inside our own. About 80% of all the dense molecular gas in the Milky Way sits in the CMZ, and its gas properties — density, turbulence, temperature, and pressure — are extreme compared to the rest of the disk. Because nearby starburst and high-redshift environments share many of these properties, the CMZ is the closest place we can actually resolve individual star-forming cores under conditions that resemble the early universe.
She showed that gas in the CMZ is extremely filamentary across all scales, and that the relationship between dense gas and star formation rate is unusual: when individual clouds in the CMZ actually form stars, they form them much like clouds elsewhere in the galaxy, but a large fraction of the dense gas in the CMZ never engages in star formation at all. Battersby argued that this is likely because so much of that gas is being shaped by flows toward the black hole and the strong turbulence and dynamics of the central environment, and it never cools and collapses into stars.
She closed with the simulation and machine-learning side of the program. Her group runs zoom simulations that can follow individual star-forming regions and can resolve down to CMZ scales while still capturing the full ~5 kpc bar driving gas inward. To extract more from these simulations than just side-by-side image comparisons, the team built a GPU-accelerated radiative transfer code that runs roughly 10,000 times faster than existing codes They generate hundreds of thousands of synthetic observations and use them to train an encoder–decoder convolutional neural network that learns to predict the top-down structure of a region from the side-on view we actually observe. Applied to the CMZ, the network produces 3D reconstructions that are physically plausible and broadly consistent across independent training runs.