Editor’s Note: This week we’re at the 244th AAS meeting in Madison, WI, and online. 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 June 17th.
Plenary Lecture: Scanning the X-ray Sky for Dark Matter, Kerstin Perez (Columbia University) (by Nathalie Korhonen Cuestas)
Throughout the universe, we’ve detected the indirect signatures of dark matter: a hypothetical form of matter that does not interact with normal matter through electromagnetism and makes up most of the matter in the universe. It’s seen in the rotation curves of galaxies, through gravitational lensing in the Bullet Cluster, and in the anisotropies of the cosmic microwave background. Dr. Kerstin Perez (Columbia University), the conference’s last plenary speaker, works to characterize the properties of dark matter through observations of X-ray photons, bringing us closer to understanding the matter that makes up so much of the universe.
It’s possible that dark matter particles interact through forces that we can’t currently understand using the standard model, producing photons with X-ray wavelengths. Perez leverages these interactions to look for “extra” photons as a signature of dark matter. However, it can be difficult to pinpoint which photons are coming from dark matter particles, and which photons are produced by normal, baryonic matter. Ideally, you’d observe a region with a high dark matter density and a low (or very well understood) background of photons from baryonic sources. Even though this technique can be tricky, Perez noted that even when a photon excess doesn’t end up being due to dark matter, it can still tell us something new about the background source.
To make her observations, Perez uses the NuSTAR instrument in a novel way. Normally, astronomers use photons that have traveled through the optics of the NuSTAR telescope, resulting in a small field of view. But one astronomer’s trash is another astronomer’s treasure; Perez uses photons that have come in from very large angles and hit the detector directly, rather than going through the optics system. This results in a larger pacman-shaped field of view, which can be cleverly aligned with a dark matter halo or a star, allowing Perez to search for photons produced by dark matter.
Dark matter particle theories come in lots of different flavors, and in her talk, Perez focused on two: sterile neutrinos and axions. Both types of particles only interact with gravity, and they could address other open questions in particle physics, not just that of dark matter. Perez showed observations of dark matter halos and Betelguese (a well-observed red supergiant) from NuSTAR, and while neither yielded a clear cut detection of dark matter, they do put strong constraints on the properties of dark matter. As these constraints get more stringent, we can get closer to either ruling out a theory or homing in on the true value. Perez ended by highlighting three proposed X-ray missions (HEX-P, GRAMS, and IAXO) that could apply this method with more precision, hopefully bringing us closer to understanding the nature of dark matter.
Editor’s Note: This week we’re at the 244th AAS meeting in Madison, WI, and online. 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 June 17th.
Helen B. Warner Prize Lecture: The Lives and Deaths of Star Clusters, and the Black Holes They Make Along the Way, Carl Rodriguez (University of North Carolina at Chapel Hill) (by Catherine Slaughter)
The Wednesday morning plenary lecture was given by this year’s Warner Prize recipient, Carl Rodriguez (UNC Chapel Hill). Rodriguez is a theoretical and computational astrophysicist, whose recent research focuses on the gravitational waves that could be produced by black holes in globular clusters. He opens the lecture emphasizing how our population of observed black holes has changed dramatically since 2015, when LIGO first came online. While gravitational waves have been used to observe a huge number of new black holes, Rodriguez highlighted a smaller set has been identified using radial velocity and (using Gaia) astrometry.
Rodriguez highlighted that newly identified populations often include black holes in the known upper mass gap; there are few black holes found with masses ranging from 65 to 135 times the mass of the Sun. The mass gap is a predicted result of late-stage stellar evolution, when stellar remnants of these masses are torn apart in highly energetic pulsational pair instability supernovae. We simply don’t expect to see isolated black holes of this size. Additionally, the observed astrometric binaries have masses and separations that are largely inconsistent with the expected parameters of common-envelope evolution of isolated binary stars. Rodriguez explained, however, that both of these oddities may be explained by the unique conditions inside globular clusters.
Rodriguez goes on to describe how black holes move throughout a globular cluster. Generally, dynamical friction causes very massive, dense objects to preferentially move toward the center of the cluster over relatively long timescales (~100 million years). Once they’re in generally the same space, black hole binaries can form through three-body system mechanics. In classical Newtonian mechanics, it is not possible for two unbound point particles to enter a bound orbit via standard gravitational interactions — there is simply too much energy in the system. It is possible, however, with the introduction of a third “interloper” star, which experiences a recoil effect, carrying the extra energy away with it. This phenomenon can explain the seemingly strange orbital parameters of the astrometric binaries. The remaining binary is either kicked from the cluster, merges while in the cluster, or gets disrupted by the cluster.
Of course, this all relies on a strong understanding of how globular clusters form in the first place. In order to better understand this, Rodriguez and his research group make use of their Great Balls of FIRE simulations. This project focuses on “daisy-chaining” three types of models. First, a high-resolution cosmological simulation shows how individual molecular clouds form in galaxies. Then, a cloud-collapse simulation takes in that output and models the creation of stars from the material. Finally, an N-body simulation shows how those stars interact and dynamically evolve over time. Their final result is a simulated galaxy, with mass similar to the Milky Way, containing a similar number of globular clusters to the Milky Way. These clusters are shown to have a similar age-alignment relationship to those in the Milky Way, and — most notably — a distribution of black hole masses that includes the upper mass gap. The question then becomes how the simulated mass-gap black holes formed. Rodriguez speaks primarily about two possible mechanisms: black hole mergers and progenitor star mergers.
An image of one of Rodriguez’s slides, outlining the structure of the Great Balls of FIRE simulation. [Slide by Carl Rodriguez]
Analysis of the simulation found that a given black hole is expected to experience, in the most extreme case, two or three mergers. This is because rapidly spinning black holes release gravitational waves in a preferred direction when they merge, causing the merger remnant to be “kicked” in the opposite direction. The more mergers a black hole experiences, the higher its spin, and the harder it gets kicked, eventually getting kicked from the cluster altogether. Indeed, they find only three of these most extreme hierarchical mergers manage to survive in the cluster. It is also possible that stars themselves merge over time, creating very massive objects that could, in turn, form significantly more massive stellar black holes. Using the simulation, Rodriguez and his research group find that because these clusters form hierarchically, they at some point have density profiles that are flat and relatively unstable, leading to runaway merger events.
An image of one of Rodriguez’s slides, showing the output of the Great Balls of FIRE simulation. [Slide by Carl Rodriguez]
Ultimately, Rodriguez explains, new populations of black holes look unlike how we expect because they were likely formed under fundamentally different conditions than we expect. His simulations show that black hole binaries are ten times more efficiently formed in cluster environments, compared to isolated environments. Importantly, recent observations of binary black holes in the upper mass gap can be well explained by the conditions in globular clusters.
Press Conference: More Stars and Distant Worlds (by Ben Cassese)
Wednesday morning, Madison, Wisconsin. As some clouds gathered over Lake Monona just outside the convention center, a comparatively friendly crowd of attendees of the 244th meeting of the AAS assembled to hear the final research-focused press briefing of the conference. Titled “More Stars and Distant Worlds,” this session had presentations split between individual interesting objects and looks towards future observations.
First up was Mary Barsony, who along with collaborators discovered an unusual and striking pair of young stars using the combined powers of ALMA and JWST. The researchers came upon this rare find after noticing something strange in archival images of a triple star system. Although two of the three members appeared about two million years old, measurements indicated that the third was somehow much younger. A closer look at this outlier revealed that what had previously appeared to be one strange star was actually a tightly bound pair, both of which are spewing out long jets of material. Intrigued, they observed the system again, this time using ALMA. This second look revealed nearly edge-on, skirt-like disks of gas around each star. This unique arrangement is an interesting laboratory to test theories of stellar formation and outflows, and a powerful demonstration of the benefits of combining multiple cutting-edge datasets. [Press release]
Next was Breanna Binder, California State Polytechnic University, Pomona, who jumped beyond the cutting-edge facilities of today and instead spoke about the work required to build the next generation of Great Observatories. The Habitable Worlds Observatory (HWO) currently exists only on paper, but by the 2040s, it should hopefully be a real, gigantic space telescope hard at work discovering and characterizing Earth-like planets. Before engineers and technicians can begin bolting together the observatory, however, astronomers need to figure out exactly where they want to aim the thing and what performance specs they need to achieve their ambitious goals. As part of that effort, Binder and collaborators went through a list of about 200 promising target stars to check which of these were amenable to hosting a habitable planet. They found that about a third of them had previously been observed by X-ray telescopes, and in many cases, these archival observations revealed a disappointing but important reality. Although many of their potential target stars appeared docile in the visible wavelengths, a good portion of them are furiously emitting X-rays that are strong enough to (likely) doom any chance of life emerging on the surfaces of their planets. Her presentation emphasized that while the road to HWO will be long, by the time the telescope reaches the launchpad, it’ll be powered on its journey to space both by not only its rocket but also by decades of planning. [Press release]
Next was Roman Gerasimov, University of Notre Dame, who quickly informed the audience that he is “Paid to figure out where the periodic table came from.” He goes about this substantial task by trying to find ancient brown dwarfs and measure their compositions. Brown dwarfs are too small to sustain nuclear fusion in their cores, which means that after being born bright and hot, they fade and cool over time. If one can find a collection of brown dwarfs that all should be around the same age, say a collection that lives in the same globular cluster, then measure their temperatures, the scientist could use them as “galactic chronometers” to estimate the age of the system. That’s exactly what Gerasimov and collaborators did: using images from JWST, they identified three ancient brown dwarfs in a globular cluster named NGC 6397. These puny, sub-Jupiter-sized worlds are likely among the oldest objects in our galaxy, and also likely are just the first of hundreds of similar discoveries. Gerasimov estimates that just one more set of JWST observations taken about three years from now would reveal hundreds more, since the longer baseline would allow the team to distinguish between members of the cluster and faint objects that happen to lie in front of or behind it.
Finally was Juliette Becker, University of Wisconsin-Madison, who described recent modeling of the “perilous” journey a planet with an ocean must embark on as its star grows old. This journey has elements of a good action movie: in order to reach a happy ending where the planet retains its ocean and travels on a stable orbit around its aging white dwarf, it must survive two distinct challenges. First, as its host expands from a typical main-sequence star into a red giant, the planet must avoid getting engulfed by the suddenly enormous central body (for those curious, when our own Sun becomes a red giant, Mercury and Venus will almost certainly fall prey to the ballooning star, though the jury is still out on whether Earth will similarly suffer). Should it successfully avoid getting eaten, then patiently wait out the star’s inevitable shrinkage from a red giant into a puny white dwarf, the planet will now find itself far too far away and cold for anything liquid to remain on its surface. In order to save its ocean, the planet must be kicked inwards towards the white dwarf by some other object in the system, then survive the resulting high-eccentricity migration and tidal dissipation required to land on a close-in, stable, warm orbit.
Becker has practical motivations for fleshing out the odds of each step in this string of hypotheticals, since planets around white dwarfs are significantly easier to characterize than planets around more generic solar-type stars. That’s because the primary technique astronomers use to measure the atmospheres of close-in planets, the transit technique, returns stronger signals as the radii of the star and planet become more similar. So, Becker and collaborators wanted to assess whether it would be worth our time to put the time into surveying these stars in the first place. Their conclusion? Although an ocean could technically survive the journey laid out above, “it’s not an easy process,” and it’s unlikely that a large portion of white dwarf planets have oceans.
Plenary Lecture: When Data is Not Enough: Illustrating Astrophysics for the Public, Robert Hurt (Caltech/IPAC) (by Will Golay)
Robert Hurt is a researcher at IPAC, an institution based at Caltech that supports four central data archives and 12 different NASA missions. Hurt is a self-described “AstroVizicist,” an expert in visualizing astronomical data for researchers and the public. In his talk, he aimed to motivate the importance of artistic visualization and its role in science communication.
Hurt shows one of the first pieces of acrylic artwork he made early on in his life, an image of a galaxy with several key features aiming to communicate how they are structured. However, Hurt points out that his galaxy painting from 1979 was missing a central bulge region. He noted that this was likely a product of the time: the images of galaxies at the time were being collected on photographic film plates, which would highly overexpose the galaxy’s central regions to have enough sensitivity to capture the lower surface brightness components near the edge. Hurt’s message is that scientific illustration is a sort of hypothesis representing our current understanding of the universe.
To determine if a scientific illustration is successful, we can ask if it is accurate, clear, and, most importantly, amazing. These three components — representing the science, communications, and art “Essential AstroViz Tensions” — can shape how we approach creating a new illustration. In any new science result, there are known facts, known falsehoods, and possibilities consistent with the data but not wholly affirmed. As a scientific illustrator, Hurt aims to capture the most important new known facts of the result, but he also mentions that we can’t possibly know everything. Sometimes, an illustrator must fill in the gaps left behind to paint a complete picture. They might even choose to specifically modify and include some “falsehoods,” such as synthetic colors or rescaling an object so it is visible in the image, to clarify the illustration (trading off accuracy for the value of communication).
Hurt then discusses several case studies of his work and how the scientific illustration process works. In one example, he shows an early image of the Milky Way that resulted in a few inaccuracies as new research emerged. So, he aimed to create a new, better illustration of what our own galaxy might look like to an external observer. Illustrating our galaxy in this way can provide insights that are otherwise challenging to understand with our “inside-out” view of the galaxy. This new image was informed by several scientific results, such as gas simulations, spiral arm models, observations along specific sightlines, and even some unpublished results. The new image ended up being so well-constructed that a feature on the far side of the galaxy, the Scutum-Centaurus Arm of the Milky Way, was so accurate that a different researcher ended up confirming some key details and contacted Hurt because he was concerned he had access to his unpublished data! The artist had simply used some basic symmetries.
The updated illustration of the galaxy incorporates updates to the original image informed by accurate science results. This image is our best guess of the Milky Way’s structure. [Slide by Robert Hurt]
Hurt concludes by highlighting his non-traditional career path and the importance of fostering non-traditional and traditional academic career skills in our students. He states that we never know where a student will end up and how their skills outside of the classroom may contribute to a new, unique future role in astronomy that we can’t even predict. It is important for mentors to foster both of these skillsets in their students, even though that might mean a student is working on something beyond their research. Hurt’s illustrations are available online and are free to share with anyone.
Press Conference: Citizen Science from the 2023/2024 Solar Eclipses (by Catherine Slaughter)
Wednesday afternoon brought with it a press conference highlighting citizen science from the 2023 (annular) and 2024 (total) eclipses. Speaking at the conference were Amir Caspi (Southwest Research institute), Angela Des Jardins (Montana State University), Dawn Davies (Hill Country Alliance) and Kate Russo (Being in the Shadow).
Composite image of the solar corona taken by his citizen science teams. The colors indicate the angle of polarization. [Slide by Amir Caspi, photo by Catherine Slaughter]
First up was Amir Caspi, reporting on the results of the Citizen CATE project. Citizen CATE featured an observing network of community participants and aimed to study polarization in the solar corona. He highlights that total eclipses provide better ground-based coronal observing than a coronagraph does because eclipses also create pseudo-dark-sky conditions. Because the coronal activity the team was searching for lasts longer than the few minutes an eclipse can be observed at a single site, the Citizen CATE team gave identical, specialized telescopes to 35 teams along the eclipse path. He highlights that the communities that participated were all allowed to keep the equipment for future science and outreach purposes. In all, more than 85% of the sites were able to obtain full or partial eclipse data for the project.
Next up to the podium was Angela Des Jardins, speaking about her eclipse ballooning project, which aimed to measure the atmospheric response to the eclipse leading up to and after totality. Stratospheric ballooning is a multi-disciplinary endeavor, and is useful because it creates space-like conditions without the need for a rocket. For the eclipse project, two teams of researchers — an atmospheric science team and an engineering team — spent the 24 hours preceding the eclipse and 6 hours proceeding, launching stratospheric weather balloons with weather sensors, accelerometers, cameras, and other student-designed experiments. Her primary goal was to observe atmospheric gravity waves (which, she highlights, are not the same as gravitational waves). The experiment was successful, with the first confirmed observations of eclipse-driven gravity waves. [Press release]
Then Dawn Davies stepped up to speak about her project, LightSound. LightSound is a solar eclipse sonification device, made for those in the blind and low-vision community to better experience eclipses. Leading up to the 2023 and 2024 eclipses, LightSound received more than 2,400 requests for devices internationally. Over the course of eight workshops, 420+ volunteers of a broad range of ages and previous building experience created more than 900 devices for libraries, museums, community task forces, blind and low vision services, national parks, senior centers, and more. The team also set up a live-streamed webinar in conjunction with the American Council for the Blind, which reached an audience of more than 2,500 people. As of now, the LightSound team is looking ahead to the 2026 and 2027 eclipses, and are hoping to implement a haptic feedback feature to the device. [Press release (PDF)]
Finally, Kate Russo took the stage to describe her project, Being in the Shadow. A clinical psychologist by trade and eclipse chaser by hobby, Russo and her collaborators work to observe the feeling of awe inspired by viewing a solar eclipse through brain wave signatures. She defines awe by two specific experiences. The first is vastness, an understanding of something greater than ourselves, and the second is accommodation, the way we re-align our perspectives accordingly. In previous phenomenological research, Russo identifies six experiences that people most often report experiencing during a total eclipse: a sense of wrongness, a primal fear, awe, connected insignificance, euphoria, and a desire to repeat (yielding the appropriately themed acronym “SPACED”). In a pilot project conducted during the 2023 annular eclipse, their primary goal was to simply test the efficacy of the brain-wave mapping technology. What Russo found, however, was that even in a non-total eclipse, they were able to observe awe in every single participant’s data. Looking forward, they are hoping to repeat the experience at the 2028 eclipse in Australia (where Russo primarily works), and possibly extend the project to other astronomical events. [Press release (PDF)]
An image of the panel at the eclipse outreach press conference. Shown (left to right) are Susanna Kohler (at the podium), Angela De Jardins, Dawn Davies, and Kate Russo. Amir Caspi presented from zoom and is not shown. [Photo by Catherine Slaughter]
Royal Astronomical Society Gold Plenary Lecture: Challenges to the Cosmological Model, John Peacock (University of Edinburgh) (by Nathalie Korhonen Cuestas)
Over the course of 67 years, modern cosmology was born and matured into the current standard model, known as Λ cold dark matter (ΛCDM). In his plenary lecture, Dr. John Peacock laid out the history of cosmology, highlighting the measurements that got us to where we are now, explained some of the possible problems with ΛCDM, and outlined how recent results address these challenges.
There’s a plethora of evidence supporting ΛCDM. From redshift measurements of Type Ia supernovae, to the large-scale structure of the universe, to the anisotropies of the cosmic microwave background (CMB), many signs point towards ΛCDM. However, there are some areas of the model that we don’t fully understand — including but not limited to the nature of dark energy and dark matter — and some areas of the model that appear to be in conflict with observations. Peacock touched on four major sources of tension — large-scale streaming velocities, the CMB dipole, Hubble tension, and lensing of the CMB — and focused primarily on the last two.
You may know that the universe is expanding at an ever increasing rate, and the Hubble constant describes the speed of this expansion. There are a number of different ways you can estimate the Hubble constant, but they generally fall into two categories. One method involves measuring the distance to and velocity of distant galaxies. These two quantities are linearly related and the slope of the line can give you the Hubble constant. Alternatively, you can calculate the Hubble constant from the temperature of the CMB, which is very precisely measured. But there’s a problem: these two methods yield different values for the Hubble constant. Typically, Type Ia supernovae or Cepheid variable stars are used to calculate the distance measurements, but, Peacock said, these methods might be introducing unknown systematic uncertainties. He also showed that when a different standard candle (J-region asymptotic giant branch stars in this case), you can get a value for the Hubble constant that more closely agrees with the CMB value.
The second source of tension Peacock discussed was the results from weak gravitational lensing studies. Mass warps spacetime, and this leads to a lensing effect that produces distorted images. If you know what the undistorted image should look like, you can use the distortions to calculate the mass that must have been along the line of sight and produced the lensing. The technique can be applied to the CMB; by measuring distortions in the CMB, you can back out the amount of mass that must have been along the line of sight. Since the CMB is the edge of the visible universe, the mass along the line of sight probes the distribution of mass throughout the universe, which is fundamentally determined by cosmology.
Peacock showed that we do in fact observe slight distortions to the CMB, and the overall distortion is in good agreement with ΛCDM. However, when distortion was broken down into different redshift intervals, astronomers found something different. When only considering the mass at high redshift, the results were consistent with ΛCDM, but this was not the case at lower redshifts, in the local universe. The result might point towards a potential time evolution in ΛCDM, specifically in the dark energy component of the model (that’s the Λ). However, Peacock was careful to emphasize that these results are still in their early stages, and further study is needed before we make any major adjustments to our cosmological models.
Solar Physics Division Harvey Prize Plenary Lecture: Dissipation and Excitation: The Role of Kinetic-Scale Waves and Instabilities in the Evolution of the Solar Wind, Kristopher G. Klein (University of Arizona)
The Karen Harvey Prize is awarded by the Solar Physics Division of the AAS in recognition of significant contributions to solar physics early in one’s career. This year, the award went to Kristopher Klein of the University of Arizona. Klein studies the solar wind — the tenuous plasma that constantly streams out from the Sun and fills the solar system. Because the Sun is by far the closest star to Earth, there are types of data that we can collect from the Sun that we simply can’t get for any other star or distant plasma environment. While Klein jokingly laments that many solar physicists interact not with pretty pictures of the Sun but instead with densely packed plots of particles and electric and magnetic fields, studies of the Sun have far-reaching implications.
Klein’s work uses simulations to understand how energy is transferred within the solar wind plasma. Energy can be transmitted by waves, instabilities, and turbulence, which transfers energy from large spatial scales to small spatial scales. Studying these factors can help researchers understand electron and proton heating, which can in turn help to interpret observations of distant plasma environments, such as the pictures of Sagittarius A*, the supermassive black hole at the center of the Milky Way.
In addition to simulations, solar physicists work with an abundance of spacecraft data: there are currently 20 missions (27 spacecraft in total) capable of making in situ measurements of the solar wind, and 14 more missions are currently being formulated or implemented. Using this fleet of spacecraft, researchers can extract the basic properties of the solar wind and derive more complex parameters, like the plasma beta (the ratio of the thermal pressure of a plasma to its magnetic pressure). Because the plasma beta varies greatly with position in the solar system, different locations within the solar wind can be used as analogs for many different plasma environments across the universe.
Klein expanded on the projects that he and his research team have undertaken to track down the ways in which energy flows within the solar wind. While important advances have been made with existing data and simulations, most current spacecraft missions measure the properties of the solar wind at a single point, taking measurements as the solar wind blows across the spacecraft. (A few missions like the Magnetospheric Multiscale mission involve multiple spacecraft working in tandem.) Klein introduced the upcoming HelioSwarm mission, which will be composed of nine spacecraft that explore the solar wind, magnetosheath, and foreshock on a variety of spatial scales to study these regions in an entirely new way. With new views of the solar wind incoming, we can expect our knowledge of the solar wind and other plasma environments across the universe to increase in leaps and bounds!
Editor’s Note: This week we’re at the 244th AAS meeting in Madison, WI, and online. 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 June 17th.
Plenary Lecture: Dark and Quiet Skies for the Future of Astronomy and of the Space Environment, Aparna Venkatesan & Teznie Pugh (University of San Francisco and McDonald Observatory, UT Austin) (by Will Golay)
Aparna Venkatesan (University of San Francisco) and Teznie Pugh (McDonald Observatory, UT Austin) started the second day of the AAS by discussing the exponentially growing challenges of protecting dark and quiet skies. Venkatesan and Pugh are co-chairs of COMPASSE (Committee for the Protection of Astronomy and the Space Environment), an AAS committee dedicated to preserving the viability of ground-based, orbital, and lunar astronomy.
There are growing threats to astronomy across the electromagnetic spectrum, the most well known being light pollution. A recent paper used citizen science reports of star visibility and found that the reduced number of visible stars can be explained by the sky brightness increasing between 7% and 10% every year for the last 11 years. If this trend continues, the number of visible stars in the night sky will halve every 10 years, an existential threat to ground-based optical astronomy. The impact on major astronomical observatories is also profound. Another recent result showed that about two-thirds of major astronomical observatories have sky brightnesses exceeding the International Astronomical Union’s recommended 10% above natural levels.
However, the threat does not end in the optical or on the ground. Radio-frequency interference is another rapidly growing problem that could wipe out ground-based radio observatories. At the other end of the spectrum, space-based nuclear power could threaten space-based high-energy observatories like Chandra (#SaveChandra). Also in space, the growing number of satellites has posed a major problem for ground-based observation. Eighty percent of all active satellites have been launched in the last four years, and 60% of active satellites are part of the Starlink constellation. As of 29 May 2024, there are 547,267 combined International Telecommunications Union (ITU) & Federal Communications Commission (FCC) applications for new frequency allocations for space-based satellites. The impact of these satellites is manyfold: from increasing the sky brightness, streaking in images, and the impact of launches (which are not yet well known), 500,000 satellites would make ground-based astronomy almost impossible. Given current predictions on satellite launchers, the Vera Rubin Observatory anticipates streaking in 30% of images during twilight hours.
A zoom-in of the radio frequency allocation plot showing the location of the 21-cm line relative to the frequency allocations. The 21-cm line is not a frequency protected for astronomy. [Slide by Aparna Venkatesan and Teznie Pugh]
The impact of brighter skies extends far beyond professional astronomers. Amateur astronomers will also suffer the same effects, and the implications on animal and bird migration patterns are just starting to be understood. Some Indigenous populations, which have already disproportionately been impacted and repeatedly displaced, rely on wayfinding with constellations and asterisms. The rising sky brightness already has measurable impacts on this navigation method by reducing the number of visible stars.
However, all is not lost! COMPASSE is taking many steps to combat these challenges. COMPASSE provides templates for local ordinances and advocates for dark skies, education, and outreach in local communities. The committee also works with government organizations like the FCC, the Federal Aviation Administration, the US State Department, etc., to provide comments on the impact of new policies on dark and quiet skies. They are increasing awareness by publishing in scientific journals and popular media outlets, and they’ve taken many more steps to begin combating this issue. Venkatesan and Pugh highlighted that the story is not complete yet, and that it is our story to write by getting involved in advocacy for dark and quiet skies.
Press Conference: From the Galactic Center to the Galactic Disk (by Nathalie Korhonen Cuestas)
The first press conference of the day included five different speakers who described their work on Sagittarius A* (Sgr A*) — the supermassive black hole (SMBH) at the center of our galaxy — and its surroundings. Sgr A* gives us a rare chance to study inactive black holes, which are otherwise too faint to observe with much detail.
The first speaker, Grace Sanger-Johnson (Michigan State University), presented X-ray observations of Sgr A*, which were taken over a period of eight years by the NuSTAR telescope. A puzzling characteristic of Sgr A* is that it flares in X-ray wavelengths. Over a period of a couple hours, Sgr A* can become up to 600 times brighter than it normally appears. The origin of these cosmic fireworks is currently unknown, but there are two main hypotheses: the flares could originate from the magnetic fields in plasma very close to the black hole, or they could be the result of a star coming too close to the black hole and losing some of its mass. Sanger-Johnson’s observations show that there is a correlation between the brightness of a flare and the hardness of a flare. Here, “hardness” refers to how much of the light emitted is at shorter, more energetic wavelengths. A harder flare has more energy at shorter wavelengths, and Sanger-Johnson found that harder flares were generally brighter. This correlation could point to two different origins for these X-ray flares: one that produces dimmer, softer flares, and another that produces brighter, harder flares. Further observations of Sgr A*’s flares will help astronomers determine if this is indeed the case. [Press release]
Next up was Jack Uteg, a rising sophomore at Michigan State University. His talk shifted focus from Sgr A* to the ring of molecular gas that resides around 100 parsecs from the galactic center. This gas, known as the central molecular zone (CMZ), can be observed in X-ray, but we know that molecular gas cannot emit at this wavelength by itself. Therefore, these X-rays may have originated from Sgr A*, and are now being reflected by the CMZ. Uteg specifically studies the emission from a region known as the Bridge Cloud. The distance between Sgr A* and the Bridge Cloud means that light takes about 200 years to travel from Sgr A* to the Bridge Cloud, where it can be reflected. This means that any observations of the Bridge Cloud tell us what Sgr A* was up to 200 years ago. Using X-ray observations taken over 24 years, Uteg reconstructed the X-ray emitting history of Sgr A* and found that around 200 years ago, Sgr A* underwent an outburst that made it 100,000 times brighter than it normally is! [Press release]
Continuing with the theme of the CMZ, Dylan Paré (Villanova University) discussed his observations of the magnetic fields in the CMZ. The FIREPLACE (Far-Infrared Polarimetric Large-Area CMZ Exploration) survey used the polarization of light from the CMZ to map the magnetic fields that thread the clouds. Paré found that the magnetic field was preferentially oriented in two directions, and that higher density regions such as The Brick (see the first inset panel in the image below) have more well-aligned magnetic fields. In the galactic disc, the opposite is observed to be true — denser clouds are less likely to have well-aligned magnetic fields. While further analysis of the different regions of the CMZ is needed, it’s possible that the observed magnetic fields are the result of a large-scale magnetic field, running perpendicular to the galactic plane, being sheared by the molecular clouds.
This picture shows you the CMZ, and the inset panels zoom in to the larger image. Radio emission is shown in yellow, emission from warm dust is shown in purple, and emission from cool dust is shown in cyan. The direction of the magnetic field is shown by the white lines. [Paré et al. 2024]
Another region observed by the FIREPLACE survey is Sagittarius C (Sgr C), an intriguing region with unusually high star formation. Jianhan (Roy) Zhao (UCLA) described the various components of Sgr C and how we can use them to learn more about the mechanisms at play in the CMZ. In the image you can see bright yellow streaks, which are radio filaments. One of these filaments originates in Sgr C, appearing to emanate from a shell of ionized gas that surrounds a molecular, star-forming cloud. One possible source of radio filaments is magnetic reconnection, a high-energy phenomenon that can accelerate electrons and cause them to emit in the radio wavelengths. In Sgr C, Zhao found that the magnetic field lines are converging towards the radio filament, supporting the idea that magnetic reconnection is powering the radio emission. The fact that the radio filament is seen to originate in an ionized region further supports this idea, since in order for electrons to be accelerated, they have to be free.
Last but not least was Dr. Anthony Minter (Green Bank Observatory), who discussed his search for dust and molecules in Smith’s high-velocity cloud. High-velocity clouds are clouds that are flying towards the Milky Way, potentially providing the fuel needed to sustain star formation. Clouds in the Milky Way contain different molecules and dust grains, but Smith’s high-velocity cloud was observed to contain no dust or molecules. It could be that the cloud originally did contain dust and molecules, but over time, they became dissociated, or, it could be that the cloud was formed from a pristine environment. In the galactic disc, we know that clouds further from the galactic plane have less dust and molecules. Minter found that clouds near the galactic center have a similar, but steeper gradient. This means that a cloud at the galactic center will have fewer molecules and dust grains than a cloud at a similar height from the galactic plane, but over the galactic disc. These kinds of abundance patterns help us to understand the structure of the Milky Way and potentially help reconstruct the events that determined the evolution of our galaxy. [Press release]
Unlocking the Mysteries of Exoplanets: The Crucial Role of Laboratory Research, Erika Kohler (NASA Goddard Space Flight Center) (by Catherine Slaughter)
This summer’s AAS meeting is a joint session with the Laboratory Astrophysics Division (LAD). As part of this joint meeting, Dr. Erika Kohler (NASA Goddard Space Flight Center) gave Tuesday’s midday plenary lecture. In this talk, Kohler promoted the use of lab-based experiments in astrophysical research and highlighted a number of her group’s projects, including the prep work for the forthcoming Deep Atmosphere Venus Investigation of Noble gases, Chemistry, and Imaging (DAVINCI) mission.
The talk starts out posing a question that motivates much of the work we do as scientists: “We found it, why not study it?” Kohler describes how recent technological innovation has allowed us to develop advanced spacefaring probes and respond to this question using in situ measurements of solar system planets. The catch, she notes, is that even the most advanced tech could not make in situ measurements of exoplanets. From this, Kohler outlines her talk’s key takeaways: that lab research is fundamental and complements all other astrophysics work, and that (given the cross-disciplinary nature of exoplanet research) communication pathways and user engagement propel us forward. To underscore these ideas she gives two examples from her own research.
The first comes from a study of cloud formation in exoplanet atmospheres. Solar system planets, Kohler explains, represent a very limited region of possible exoplanet parameters, especially in terms of atmospheric pressure and temperature. “If you’re only designing experiments to describe [the solar system planets],” she says, “you’re missing a whole universe out there.” In the project, Kohler and her team used lab-based experiments to recreate the very extreme atmospheric environments found on distant exoplanets. Their goal was to experimentally determine saturation vapor pressure curves — mathematical descriptions of the pressures and temperatures at which a given material will form clouds — for a number of known and expected molecules in exoplanet atmospheres. The preexisting curves were created using calculations based on Earth-like conditions. They found that the heights at which clouds form in a given atmosphere are different in extreme environments, which changes our interpretation of possible exoplanet atmosphere observations. This is a result that could only be reasonably obtained in a lab setting.
A slide from Kohler’s talk, showing the orbital distance–mass parameter space scatter plot for identified exoplanets at present. [Slide by Erika Kohler]
The second example is a study conducted in preparation for the launch of DAVINCI. The mission will include a probe that descends down to the surface of Venus, taking images of the surface in near-infrared and making atmospheric measurements along the way. In order to obtain usable images, however, it is important to ensure that the atmosphere of Venus is reasonably transparent to infrared light. Kohler’s group began by studying the changing opacity of CO2 in the varying temperatures and pressures of Venus’s atmosphere. They conducted a simulated descent, taking observations of infrared transmission through CO2 at conditions mimicking the atmosphere from 55 to 7 km above the surface. In doing so, they are able to identify the wavelengths at which the atmosphere can be expected to become opaque at some point in the probe’s journey. Along with being foundational work for the future DAVINCI mission, these experimental results have huge implications for JWST, which observes in the mid-infrared, highlighting the necessity of lab work as a supplement to distant observation.
A slide from Kohler’s talk showing a sprawling graph-map diagram of the many features studied in exoplanet research. [Slide by Erika Kohler]
Kohler finishes the talk encouraging the crowd to pursue three actionable challenges: 1. Talk to people in other subfields. 2. Look at the assumptions in our own research, and see if they’ve ever been verified in the lab. 3. Take a multi-method approach to research, combining lab-based, modeling, and observational techniques. She leaves us with a reminder that lab-based research allows us to both describe and predict astrophysical observations, and that we want to be prepared before first light.
Press Conference: Massive Black Holes and Surprising Spirals (by Kerry Hensley)
Fan Zou (Penn State University) opened the afternoon press conference with a discussion of supermassive black hole growth. Despite nearly all massive galaxies having supermassive black holes, it’s still not known exactly how these objects get so massive. Accretion and mergers are the two possible growth mechanisms, and researchers need to understand both processes to reconstruct the growth history of black holes. Zou explained that astronomers study black hole accretion through X-ray observations, and they study mergers through supercomputer simulations. Combining results from Chandra X-ray Observatory, eROSITA, and XMM-Newton — three premier X-ray observatories — with output from the IllustrisTNG simulations, Zou’s team found that accretion played a larger role in black hole growth than mergers did under most circumstances. The growth rate due to both mechanisms was higher in the early universe, although the two mechanisms have declined at different speeds. Today, mergers play a larger role relative to accretion than in the early universe. [Press release]
Robert Wheatley and Catherine Grier (University of Wisconsin-Madison) reported on their study of a quasar: a supermassive black hole with a hot, luminous accretion disk that emits radiation across most of the electromagnetic spectrum. Quasars often have powerful winds or outflows that travel at millions of miles per hour out from the accretion disk. Because these winds can block the light from the hot accretion disk, they are visible in quasar spectra as absorption lines. Using observations from the Sloan Digital Sky Survey Black Hole Mapper Reverberation Mapping Project, Wheatley, Grier, and collaborators demonstrated that the outflows from the quasar SBS 1408+544 (also called SDSS-RM 613) have been accelerating over the past eight years because of radiation pressure from the luminous accretion disk. This acceleration was evident from the blueward shift of an absorption line of carbon. While previous observations have hinted at accelerating quasar outflows in a handful of spectra, this new work uses 130 spectra, providing an unprecedented new look at this phenomenon. [Press release]
Next, Riccardo Arcodia (MIT) presented a study on massive — not supermassive! — black holes in low-mass galaxies. Studying these somewhat-less-than-supermassive black holes in the nearby universe can help researchers understand how supermassive black holes grew from lower-mass seeds in the early universe. Accreting black holes emit light across the electromagnetic spectrum and can be highly variable, so Arcodia’s team searched for low-mass galaxies that are variable in the optical and infrared to identify candidate massive black holes. Of the 200 candidate massive black holes, only 17 emitted X-rays. This result is unexpected because accreting supermassive black holes are extremely luminous in X-rays, and the team estimated that X-rays from the black holes in their sample should have been detectable. This might mean that lower-mass black holes have a different accretion mode compared to supermassive black holes, possibly because of the lower gravity, clumpier interstellar medium, or other factors. [Press release]
Lastly, Vicki Kuhn (University of Missouri Columbia) presented some new results from JWST on spiral galaxies. Previous studies using the Hubble Space Telescope have found that there are very few spiral galaxies earlier than a redshift of z = 2, which corresponds to when the universe was just a few billion years old. Kuhn’s team identified 873 galaxies with high stellar mass and redshifts between 0.5 and 4 in observations from JWST, which can look farther back in time than Hubble can. A team of six researchers visually classified each galaxy in the sample as spiral or not, and they found that JWST sees more spirals than Hubble did, especially at low redshift. To account for the fact that spiral structure is harder to discern at high redshift, Kuhn’s team created a sample of mock high-redshift galaxies. After determining how redshift affects the fraction of galaxies in which spiral structure is visible, the team found that about 30% of galaxies are spirals out to a redshift of z = 3. This is far more spirals than found in previous studies, suggesting a need to recalibrate our expectations for when and how spiral structure formed in early galaxies. [Press release]
Plenary Lecture: Leveraging AI to Transform the Astronomy Data Revolution into a Discovery Revolution, Cecilia Garraffo (Center for Astrophysics | Harvard & Smithsonian) (by Will Golay)
Cecilia Garraffo is a researcher at the Center for Astrophysics | Harvard & Smithsonian and the director of AstroAI. She is an expert in machine learning (ML) and artificial intelligence (AI) data analysis methods. She has developed novel techniques for using machine learning to uncover unique and exciting results from large astrophysical datasets. In her talk, she aimed to highlight what AI can contribute to research in astrophysics.
Garraffo motivated the need for AI methods by reminding us of an important point: although we are building massive observatories that will be coming online in the next five to ten years, are we, as a community, prepared for the immense data influx that will ensue? Once observatories like the Vera Rubin Observatory and the Square Kilometre Array begin observing, we will generate more data in one year than all currently existing astrophysical data. We are entering the era of petabyte astrophysics, an era we are not yet prepared to begin. The data volumes are not the only consideration: as astrophysics research becomes increasingly multi-wavelength and multi-messenger, causing datasets to become heterogeneous, it is even more critical that we have methods that can unify the picture and maximize the scientific value of such unique datasets.
AI is one tool we can apply to begin preparing for the upcoming massive influx of data. Garraffo argues that AI has the unique ability to search for patterns and classes intentionally (even if we don’t know what those patterns are a priori), enabling a chance for discovery spaces that would otherwise be inaccessible in smaller datasets. Even the most basic dimensionality reduction and clustering methods have successfully identified new anomalies in large datasets that we can later follow up on.
How exactly do we execute such a search using ML methods? The astronomy community needs experts in AI to help develop strategies specific to our kind of data. Astronomical data often differs from the data used to train large language models (LLMs) in several ways. Our data are biased and complex, could be multimodal, almost always incomplete, and undoubtedly sparse. To address these issues, we need to take specific steps to prepare our data and our ML models, which require user expertise in identifying methods and successfully applying them in the context of astrophysical research.
Garraffo then shared several examples of how AI has been used in various research contexts inside the AstroAI collaboration. One particularly striking example she shared was using ML methods to generate new “realistic” images of a black hole accreting material for comparison with images from the Event Horizon Telescope (EHT). Since general relativistic magnetohydrodynamic simulations are costly to run, we can use ML methods to interpolate between the model’s parameters. In the case of EHT, they are interested in using these methods to generate images of a black hole with differing spins, significantly affecting how the accretion will appear in EHT images.
A slide from Cecilia Garraffo’s presentation showing two images of a black hole that were generated by simulation and one image that was generated from ML methods. Garraffo is illustrating that the human eye is not well suited to distinguish between these cases. [Photograph by Will Golay]
Although ML astrophysics methods are just starting, Garraffo is excited to continue sharing them and educating the community via the AstroAI collaboration. The collaboration aims to educate students about how AI methods can be used in astrophysics research and begin developing a new era in which these methods are common throughout a wide variety of subfields. Stay tuned for more updates about the AstroAI collaboration at the Center for Astrophysics on their website!
Plenary Lecture: With a Wild Surmise: A New Era of Exoplanet Exploration, Tom Beatty (University of Wisconsin at Madison) (by Jessie Thwaites)
Wrapping up today’s talks was Dr. Tom Beatty, whose plenary lecture explored exoplanets, specifically how we can classify them. We already know of more than 5,600 exoplanets, and that number just keeps growing! He discussed how we can measure a planet’s atmosphere to learn how exoplanets form, explore what makes a planet habitable, and search for signatures of water and oxygen that would be necessary to support life.
The attempt to classify exoplanets is multifaceted, he says, including searching for trends in their mass, gravity, age, metallicity, clouds, specific elemental abundances, and more. But these quantities have complicated relationships; for example, he discusses how ambiguity in cloud models on the planet’s surface can change the abundance measurement we get. These measurements of the spectra of these planets are made via transmission (seeing the spectral lines that appear when the planet passes in front of its star) and emission (seeing the spectral lines than disappear when the planet passes behind its star).
Central to the themes of his talk were how improvements in technology have made these detailed and accurate measurements possible. Initially, these measurements were done with the Spitzer Space Telescope, and massively improved upon with the Wide Field Camera 3 instrument on the Hubble Space Telescope, which allowed for more precise and spectroscopic measurements. And now, with JWST’s improved sensitivity, we can measure carbon and oxygen molecules in exoplanet atmospheres for the first time, get spectroscopic measurements of clouds, and even search for signatures of life on exoplanets!
New questions about our understanding of exoplanets, and properties of exoplanets that are currently being studied. [Slide by Tom Beatty]
But searching for biosignatures requires more than just understanding the atmosphere on these planets, he says, so researchers have formed the Wisconsin Center for Origins Research (WiCOR) to bring together astronomy, chemistry, integrative biology, geoscience, bacteriology, botany, and atmospheric and oceanic studies to search for life on exoplanets in a multidisciplinary way.
Editor’s Note: This week we’re at the 244th AAS meeting in Madison, WI, and online. 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 June 17th.
Fred Kavli Prize Plenary Lecture: UNCOVERing Astronomical Gems from Our Backyard to the Edges of the Observable Universe, Rachel Bezanson (University of Pittsburgh) (by Nathalie Korhonen Cuestas)
JWST has pushed our cosmic horizons well beyond what we could previously observe. Its incredible sensitivity, instrument suite, and wavelength coverage makes it excellent at observing previously invisible distant galaxies. These early galaxies can help us understand how galaxies form stars, when they stop growing so rapidly, and how a central supermassive black hole might affect galaxy growth. During this year’s Fred Kavli Plenary Lecture, Prof. Rachel Bezanson discussed how her JWST program UNCOVER is helping us answer these questions.
This diagram shows how a massive galaxy cluster can bend the light rays coming from a more distant galaxy, resulting in magnified images. Click to enlarge. [NASA, ESA & L. Calçada; CC BY 4.0]
UNCOVER uses the power of gravity to unlock a Pandora’s box of high-redshift galaxies. Normally, light travels in a straight line, but this can change if a heavy enough object warps spacetime enough to bend light. This effect is known as gravitational lensing and results in the images of galaxies being distorted and, more importantly, magnified. Gravitational lensing allows us to see galaxies that would otherwise be too faint and resolve galaxies that would otherwise be too small.
By observing galaxies which have been lensed by a massive galaxy cluster Abell 2744 (also known as Pandora’s cluster), Prof. Bezanson is challenging our previous assumptions about galaxy evolution. Many of the galaxies she’s observed are very massive — they can be as massive as the Milky Way, yet their age is just 3% of the age of the universe — and have signatures of evolved stellar populations in their spectra. Some also have supermassive black holes that are much more massive than we’d expect. Our models for galaxy evolution have to be able to explain how these galaxies and their black holes have grown so large, so quickly. Further JWST observations and development of our theoretical models will begin to answer long-held questions and bring up new ones.
Press Conference: Disks, Atmospheres, and Astronomy from the Moon (by Kerry Hensley)
The first presentation of the AAS 244 press conference series, given by Lisa Prato (Lowell Observatory), tackled the topic of circumstellar disks. Circumstellar disks occur naturally during star formation, forming when a swirling cloud of gas collapses and creates one or more stars. These disks are the sites of planet formation and dissipate after roughly 10 million years, although the time frame can be far shorter. It’s not yet known what sets the lifetime of a circumstellar disk. To learn more, Prato’s team studied planet-forming disks around binary stars. Stars in a binary system have the same age, composition, and radiation environment. Differences in the disks around these stars can then be traced to differences in the stellar properties, such as mass and rotation rate. Prato’s team used the Keck Observatory and the Atacama Large Millimeter/submillimeter Array (ALMA) to observe the circumstellar disks of the FO Tau and DF Tau binary systems. The two stars of FO Tau each had a tidy circumstellar disk and appeared similar in the data from both observatories. Keck data suggested that one star in the DF Tau system lacked a disk, but ALMA showed something different: the secondary star in the system has a disk with a large gap in the middle! Prato proposed that a possible misalignment of the secondary star’s disk could be related to the formation of the cavity. [Press release]
Moving forward in the planet-formation process, Christine Chen (Johns Hopkins University/Space Telescope Science Institute) reported on JWST observations of a debris disk around the young, nearby star Beta Pictoris. In the debris disk phase, the original gas and dust of the disk have mostly dissipated, and planet formation is underway; as planetesimals form, they collide and create rocky rubble and dust. Twenty years ago, the Spitzer Space Telescope detected several types of dust around the star Beta Pictoris, which is known to be orbited by two giant planets. Looking at the star again with JWST in 2023, Chen’s team saw that two of the dust components — hot dust and small, cold forsterite dust grains — had disappeared. Piecing together the clues, Chen’s team proposed that a collision between giant asteroids some 20–30 years ago created the dust seen by Spitzer; by the time JWST turned toward the system, radiation pressure had whisked the small dust grains out of the system, resulting in the less-featured spectrum seen today. Other data support the collision scenario, including 2022 JWST observations of a “cat tail” feature in the disk’s emission and 2014 ALMA observations of carbon monoxide gas. [Press release]
Moving from planet formation to fully formed planets, Thomas Beatty (University of Wisconsin-Madison) presented new JWST observations of a sub-Neptune exoplanet named GJ 3470 b. Astronomers can compare the composition of exoplanet atmospheres to the composition of protoplanetary disks to understand the planet-formation process, much like a baker might try to discern the steps needed to make a finished cake from a list of ingredients. Astronomers have mostly looked for carbon and oxygen in exoplanet atmospheres over the last two decades, but there are many other ingredients to look for. Using JWST to observe GJ 3470 b, Beatty’s team found water, methane, carbon monoxide, carbon dioxide, and a surprising compound: sulfur dioxide. Sulfur dioxide has been seen in the atmosphere of another exoplanet, WASP-39b, which is twice as hot and a hundred times more massive than GJ 3470 b. The researchers didn’t expect to find so much of this molecule in the atmosphere of a small and cool exoplanet — in fact, the planet’s atmosphere contains more than a million times more sulfur dioxide than expected. Sulfur dioxide is a major new ingredient that can be used to trace the formation of small sub-Neptune exoplanets, which are one of the most common types of planets. [Press release]
“Selfie” by ROLSES showing the prematurely deployed antenna, circled. [Intuitive Machines]
Lastly, Jack Burns (University of Colorado Boulder) presented the results of a recent mission to land a radio telescope near the Moon’s south pole: Radio wave Observations at the Lunar Surface of the photo Electron Sheath (ROLSES). For the first time in more than 50 years, NASA landed a scientific payload on the Moon in February 2024. While there were a few bumps along the way — a 2.5-meter antenna deployed unexpectedly in transit, and a failure of the laser-guided navigation system resulted in a too-hard impact that snapped one of the landing legs and tilted the lander nearly on its side — the mission was a success. The lander, observing Earth as would a distant observer for whom our planet is an exoplanet, collected Earth’s radio signals. This is essentially a redo of Carl Sagan’s SETI experiment, which used a close flyby of Earth by the Galileo spacecraft to understand how our planet might look to an extraterrestrial observer. The ROLSES radio spectrum greatly improved upon the measurements from Galileo, providing crucial data to be compared to future observations of exoplanet radio emissions made from telescopes on the far side of the Moon. The future of lunar radio astronomy is bright: NASA has already funded a successor to ROLSES that will fly in 2026, along with the Lunar Surface Electromagnetics Experiment-Night (LuSEE-Night) mission (also in 2026), which will perform cosmological observations from the lunar farside, shielded from terrestrial radio emissions. [Press release]
Plenary Lecture: Ices in Our Backyard: Searching Ices in the Solar System with JWST, Noemi Pinilla-Alonso (Florida Space Institute) (by Will Golay)
Noemí Pinilla-Alonso, a planetary science professor at the Florida Space Institute and the University of Central Florida, gave the final talk of the inaugural morning of AAS 244. In her talk, she described the different kinds of ice in our solar system and discussed what they can tell us about the formation of planetary systems and their relationship to the interstellar medium and molecular clouds.
Ices in our solar system encode information about various stages of its formation history. The most distant objects, broadly categorized as “trans-Neptunian objects” (TNOs), span a spectrum of ice histories. Some of these dirty, icy bodies never melted and thus trace the conditions of the solar nebula. Others have undergone some melting and differentiation; observations of these objects can probe the process of planetary growth and the diffusion of molecules throughout the solar system.
Although TNOs can provide many insights into the solar system’s formation (and the formation of planetary systems in general), they have remained largely unexplored because they are often small and distant, making detailed photometric and spectroscopic studies challenging. Pinilla-Alonso highlighted how JWST, the premier space telescope for infrared observations, will uncover the secrets of our most distant solar system members with its unprecedented spectroscopic capabilities.
A slide from Noemí Pinilla-Alonso’s plenary lecture showing examples of the three spectral groups of trans-Neptunian objects: bowl, double-dip, and cliff-type. Click to enlarge. [Slide by Noemí Pinilla-Alonso]
Pinilla-Alonso shared preliminary results from her Cycle 1 JWST program, DISCo. In this program, her collaboration used the NIRSpec and MIRI instruments to collect infrared spectra of ~60 TNOs that they identified as having various properties. With these observations, they found that the spectra of TNOs fall into three major groups: bowl-type, double-dip-type, and cliff-type. These three categories are physically characterized by the molecules that create these features in the infrared spectra. The bowl-type TNOs are rich in water ice, with some carbon dioxide. The double-dip-type has lots of carbon dioxide and carbon monoxide ice and evidence of more complex organics. Finally, the cliff-type sources have many organic molecules but less carbon dioxide and carbon monoxide.
A slide from Noemí Pinilla-Alonso’s plenary lecture showing how the three spectral classes of trans-Neptunian objects may represent a transition in the distance at which these objects formed from the central star in the protoplanetary disk. Click to enlarge. [Slide by Noemí Pinilla-Alonso]
Although previous observations had only hinted at a transition in the composition of TNOs based on where they formed relative to the “ice lines” (or the distances at which a particular molecule freezes), these JWST observations provide a much stronger case for the origin of TNO diversity. Pinilla-Alonso highlighted that these results indicate we can use the properties of TNOs to learn about the primordial planetesimal disk in a new way. Her collaboration is completing additional analyses of their JWST data, and we should expect more results to come soon.
Press Conference: Stars and Their Antics (by Ben Cassese)
In the afternoon, attendees once again filed into the press briefing room ready to consume another round of news-worthy astronomy research. This session, titled “Stars and Their Antics,” contained talks on individual weird stars, the motions of enormous clusters, and some of the earliest explosions in the universe.
Up first was Adam Burgasser, University of California San Diego, who set the tone with a presentation on a newly discovered speedy star. This object, initially flagged through the citizen science program “Backyard Worlds: Planet 9” doesn’t provide observers the strongest first impression. It’s dim, red, and at only 8% the mass of the Sun with a surface temperature of about 2000K, it easily fits into the “L subdwarf” category of diminutive stars. But, what it lacks in presentation it more than makes up for with pep. Burgasser and colleagues clocked in moving at more than 100 km/s along the line of sight and more than 450 km/s in total. That’s more than a million miles an hour, or so fast that this star has a good chance of escaping the Milky Way altogether. So far the team is not sure how this star got so fast: it may have been kicked around by a supernova, or scattered off a black hole, or it could have fallen in from a satellite galaxy. However it got started, though, it won’t be around for long (cosmically speaking), and the researchers hope that additional measurements can help reveal both where it came from and where it’s going. [Press release]
Up next was Janus Kozdon, a graduate student at Clemson University, who told the assembled audience about his work on a protoplanetary disk with a mysterious line profile. After models of the disk failed to provide a good fit, Kozdon and collaborators realized they could reproduce what they were seeing by considering not just one disk of emitting material, but a pair of two concentric ones. They landed on a best-fitting solution with two nested, eccentric disks, aligned so that their long axes face perfectly away from one another. This eccentricity was likely induced by a baby planet still in the process of growing and forming, a rare and exciting find. [Press release]
Next was Ravi Sankrit, Space Telescope Science Institute, who shared his work on a symbiotic nova named HM Sagittae. This star, though “nondescript” when viewed in a contemporary single snapshot, has led an interesting life over the past half-century. Back in 1975, this star loudly announced to the world that it was actually a pair of tightly bound stars: an accreting white dwarf and a pulsating red giant called a Mira variable. This announcement came in the form of an explosion: material that had been siphoned off the Mira and onto the surface of the white dwarf ignited, and the system grew hundreds of times brighter thanks to the thermonuclear fireball. The pair have felt the effects of the explosion ever since and have been slowly fading towards their original brightnesses. Sankrit shared a comparison of observations taken each decade, including recent ones collected by the Cosmic Origins Spectrograph aboard the Hubble Space Telescope. By watching how different emissions lines have evolved over time, the researchers are beginning to model the long-term relaxation of this feisty system. [Press release]
Sankrit was followed by Cameren Swiggum (whose hometown is Madison, WI!) from the University of Vienna. Swiggum and collaborators used data from the Gaia spacecraft to trace the trajectories of the nearest, youngest star clusters backwards in time. The team found that, intriguingly, the clusters seem to converge on three distinct but nearby locations about 30 million years ago. These locations must have been huge, dense, chaotic regions that spawned numerous stars quickly. These conditions are ideal for forming large stars that live fast and die young, and the team estimates that there could have been more than 200 supernovae caused by stars born in these progenitor clusters. [Press release]
Christa DeCoursey, University of Arizona, and Justin Pierel, Space Telescope Science Institute, rounded out the session with an update on the JADES transient survey. JADES, or the JWST Advanced Extragalactic Survey, is an enormous collaborative effort that involves aiming JWST at a tiny patch of sky for more than 100 hours, waiting a year, then imaging that same patch again. The resulting ultra-deep images contain some of the most distant galaxies ever discovered. Equally interesting, however, are the smaller objects that appear in just one of the two photographs. A few dozen (relatively) bright dots appear in one image but not the other, meaning they must have flared up or died down quickly. The team identified these as supernovae, and given the locations and properties of their host galaxies, they must be some of the most distant eruptions seen to date. The Hubble Space Telescope managed to find about 20 truly faraway supernovae in 20 years, and in just one year of observations, the JADES team has already found 83 comparable events. It’s still early days, but JWST has already proven itself a capable supernova hunting machine, and the community can look forward to more observations of ancient explosions in the coming years. [Press release]
Plenary Lecture: Plenary Lecture: The Broad Legacy of George Ellery Hale: Observatories, Institutions, and Civic Development, Sam Hale (Alliance of Historic Observatories) (by Catherine Slaughter)
Each year, the American Astronomical Society’s Solar Physics Division (SPD) awards the George Ellery Hale Prize to “a scientist for outstanding contributions to the field of solar astronomy.” On Monday, to preface the AAS 244 Hale prize talk, Sam Hale, grandson of George Ellery Hale, gave a lecture highlighting his grandfather’s work and multifaceted legacy of astronomical research and the advancement of the sciences in the United States. Sam himself is not an astronomer, but he presently serves as the CEO and Board Chairman for the Mount Wilson Observatory. He is also a founding member of the Alliance of Historic Observatories, an international consortium of famed astrophysics research sites.
Yerkes Observatory, when it first opened in 1987. [Slide by Sam Hale]
As astronomers, whether or not we know his name, we are familiar with George Ellery Hale’s (GEH, as Sam Hale refers to him) legacy. In the talk, Hale laid out his grandfather’s many achievements. GEH is known for spearheading the construction of the Yerkes, Palomar, and Mount Wilson observatories, his work in heliophysics and the invention of the spectroheliograph, and his efforts to elevate American science on the world stage and establish international partnership between European and American astronomers. In addition, GEH was an original member of the AAS and founder of the Astrophysical Journal.
Interwoven with stories of his grandfather’s achievements, Hale featured many of the significant scientific discoveries made by other astronomers using the resources GEH worked to build. Of particular note is Edwin Hubble’s work on Mount Wilson, where he took the observations of distant galaxies that became our foundational evidence that the universe is expanding.
At the end of the session, Hale left the audience with the reminder that it was his grandfather’s “insatiable curiosity” that drove him through life — a curiosity that continues to benefit the field to this day.
Solar Physics Division George Ellery Hale Prize Lecture: Solar Irradiance: Earth’s Energy Source, Judith Lean (University of Colorado) (by Jessie Thwaites)
Slide showing the total solar irradiance, along with the presence of faculae and sunspots. Click to enlarge. [Slide by Judith Lean]
Following Sam Hale’s plenary discussing the life and work of his grandfather, the George Ellery Hale Prize was awarded to Dr. Judith Lean, for her work on solar irradiance. When you look up “total solar irradiance,” you’ll find that people once thought the total radiative output of the Sun was a constant — but as Dr. Lean describes, it’s anything but!
The solar irradiance is the radiative output of the Sun, which is inherently interconnected with Earth’s atmosphere and climate. The Sun undergoes an 11-year cycle, which determines how much power is emitted. It can have any number of sunspots, which decrease the Sun’s irradiance, or bright faculae, which do the opposite. The irradiance is driven by the magnetic structure of the Sun, and Dr. Lean has developed a model of the Sun’s dynamo to understand these fluctuations. That model, based on 40 years of observations of the Sun, helps us to understand the cycles of the Sun (in addition to the 11-year cycle, it also undergoes a 27-day cycle due to its rotation, a 100-year cycle, and a 2,400-year cycle that are able to change the amplitude of the minima and maxima for the cycle), and predict the Sun’s activity for the future.
Slide showing the contributions to global surface temperature changes. Click to enlarge. [Slide by Judith Lean]
This is also inherently connected to climate on Earth, and an important part of understanding climate change. Although the Sun is variable, and can raise or lower Earth’s temperature depending on the solar power output, this and other natural factors alone cannot explain the full increase in global surface temperature. The global change in temperature has already surpassed the 1.5-degree Celsius “climate threshold,” and with every 0.1 degree of additional warming we will begin to see exponential effects. By understanding the solar cycle, we can better understand the trends happening in our changing climate.
This week, AAS Nova and Astrobites are attending the American Astronomical Society (AAS) summer meeting in Madison, WI, and online.
AAS Nova Editors Kerry Hensley and Susanna Kohler and AAS Media Fellow Ben Cassese will join Astrobites Media Intern Nathalie Korhonen Cuestas and Astrobiters Will Golay, Catherine Slaughter, and Jessie Thwaites to live-blog the meeting for all those who aren’t attending or can’t make it to all the sessions they’d like. We plan to cover all of the plenaries and press conferences, so follow along here on aasnova.org or astrobites.org! You can also follow Astrobites on Bluesky at astrobites.bsky.social for more meeting content.
Where can you find us during the meeting? We’ll be at the Astrobites booth in the Exhibit Hall all week — stop by and say hello! You can also find Kerry, Susanna, and Ben at the press conferences Monday through Wednesday. AAS press conferences are open to all, and they can also be viewed on the AAS Press Office YouTube channel for anyone not attending the meeting.
AAS 244 is nearly here! The AAS Publishing team looks forward to connecting with meeting attendees in Madison, WI, and we’re excited to share a preview of upcoming publishing-related events. Attending the meeting will be Julie Steffen (AAS Chief Publishing Officer), Ethan Vishniac (AAS Journals Editor in Chief), Gus Muench (AAS Journals Data Editor), and Katie Merrell (AAS Journals Data Editor). Several of the editors of the AAS journals, including Fred Rasio (Editor of the Astrophysical Journal Letters) and Steve Kawaler (Lead Editor of the Stars and Stellar Physics research corridor) will be in attendance as well. Be sure to stop by the AAS booth in the Exhibit Hall to say hello, chat about the journals, have your data questions answered, and pick up some swag!
AAS Nova Editors Kerry Hensley and Susanna Kohler, AAS Media Fellow Ben Cassese, Astrobites Media Intern Nathalie Korhonen Cuestas, and the rest of the Astrobites team will also be available periodically at the Astrobites booth in the Exhibit Hall.
Open Science at AAS 244
Note: The following section contains links to the AAS 244 block schedule. You must be logged in for these links to direct you to the correct session; otherwise, they will take you to the main block schedule page.
On Tuesday, an oral session on outreach and education will take place in Ballroom D from 2:00 to 3:30 pm CDT. One of the talks in this session will introduce a recent special issue of the Bulletin of the American Astronomical Society that provides “eclipse science and investigations, resources for safe viewing, astrophotography, education tools and resources, personal reflections, peer-reviewed papers, explorations of individuals’ reactions to solar eclipses, descriptions of events, and discussions of logistics” for the three most recent solar eclipses to cross North America. As a bonus, this session also includes a talk by Tom Rice (AAS Education Specialist) on eclipse-related outreach to Deaf, hard-of-hearing, and signing audiences.
On Wednesday, be sure to attend the Astrophysics and Open Science splinter session. This session will bring together members of the NASA Astrophysics Division and the NSF on a panel to speak on NASA and NSF efforts to enable Open Science and take questions on this topic. You can submit your questions ahead of time; the link to submit questions is available in the abstract linked above. The session will take place 11:00 am – 12:30 pm CDT in the Hall of Ideas I.
Are you an astronomy graduate student who’s interested in science communication? Do you wish you had the opportunity to explore that interest and gain professional development without having to take time off from your graduate studies? Do you want to write for AAS Nova, report on astronomy meetings, help organize and run press conferences, and learn the ins and outs of academic publishing?
Then the AAS Media Fellowship might be for you! This position was developed in 2017 by the American Astronomical Society to provide training and experience for a graduate student in the astronomical sciences interested in science communication. The fellowship is a remote, quarter-time, one-year (with the possibility of extension to two years) position intended to be filled by a current graduate student at a US institution. The new AAS Media Fellowship term will begin in Fall 2024.
If this sounds like a good fit for you, you can get more information below or at the job register posting. Apply by 21 June 2024 by submitting your contact information, a cover letter, and a short CV to personnel@aas.org. See the job register posting for the full application details.
Essential Duties & Responsibilities
The AAS Media Fellow will report to the AAS Communications Manager. The Fellow will work the equivalent of one day per week (on a schedule that will be jointly developed and agreed upon by the Fellow, the AAS Communications Manager, and the AAS Communications Specialist) and be responsible for a wide range of duties. The Fellow will be expected to:
Assist in sharing astronomy press releases via AAS press office channels.
Regularly write and publish articles for AAS Nova.
Occasionally help to prepare other written communications such as AAS or Division press releases.
Assist in managing AAS communications such as social media accounts, postings to the AAS website, and emails to members or authors.
Serve as backup to the AAS Communications Manager or the AAS Communications Specialist during absences for daily tasks like distributing press releases and publishing AAS Nova posts.
At the AAS winter and summer meetings, help the AAS Communications Manager plan and run press conferences, help represent AAS Nova, and help organize live-blogging coverage of the meeting by Astrobites and AAS Nova.
Qualifications
The Fellow must:
Be a graduate student in good standing in the astronomical sciences or a related field at a US institution.
Receive the approval of their advisor or department chair to apply.
Receive their primary support from their home institution.
Have a keen eye for detail and accuracy.
Have the ability to absorb complex material, synthesize information, and write short articles that concisely reflect key points of the material to a target audience.
Have good working knowledge of, and/or ability to quickly master, tools such as WordPress, Drupal, Microsoft Office, and Adobe Creative Suite.
Compensation
The stipend for this position is $7,500 per year for the equivalent of one day of work per week, payable on a quarterly basis. Travel support will also be provided for travel to the summer and winter AAS meetings.
Editor’s Note: This week we’re at the 243rd AAS meeting in New Orleans, LA. 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 January 16th.
Committee on Astronomy and Public Policy Plenary Lecture: Lia Epperson (American University – Washington College of Law) (by Briley Lewis)
The final day of AAS 243 began with a plenary on an important topic: what the recent Supreme Court decisions on the use of race in college admissions mean for us as educators. In these cases, a group called Students for Fair Admissions (SFFA) challenged Harvard University and University of North Carolina (UNC) on their race-based considerations in admissions.
Epperson began by saying, “In an era where sometimes the pursuit of knowledge is maybe less appreciated than we would have liked as educators, I think it’s important for all of us to really understand the history of how we got to this moment.” Before diving into the details of the current cases, she provided an overview of how race, education, and affirmative action have been intertwined in the history of US law.
Race is embedded in the US Constitution (with the three-fifths, importation, and fugitive slave clauses), clearly indicating that our country’s founding document cared about “embedding a racial hierarchy,” said Epperson. This initial founding law has had “ripple effects on education and access to education” throughout US history, she added.
The first landmark case on education and race was Sweatt vs. Painter in 1950, when a Black student challenged a Texas law school. The Supreme Court decided that denying admission denied the student “standing in the community, traditions, and prestige customarily accorded to white students.” This ruling made clear that diversity and inclusion were to be considered a fundamental part of higher education.
Soon after, in 1954, the famous Brown vs. Board of Education ruling was issued, establishing separate education as inherently unequal. The term “affirmative action” then appeared in 1961 — not as a Supreme Court ruling or law specific to education, but from an executive order from President Kennedy initially intended for employment and contracting. The order stated that “government contractors may take affirmative action” to ensure treatment is not racially divided.
Forty years of legal precedent thereafter solidified the importance of race in holistic admissions processes, citing the benefits to democracy and pathways to leadership provided by education. Three crucial cases in this precedent were Bakke vs. Regents of UC Davis (1978), Grutter v. Bollinger and Gratz v. Bollinger (2003), and Fisher v. Texas I and II (2003, 2006). Research on K-12 schools has also shown that diverse schools improve students’ critical thinking skills, increase their civic engagement, and lead to higher graduation rates.
The Harvard case was the first to challenge race-conscious admissions, at an institution that excluded people of color for 85% of its 400-year history. UNC was founded in 1789 to serve the children of slave owners and didn’t admit their first Black student until 1951 (and even then, it was only due to a federal court order).
The questions posed before the court in these two contemporary cases were the following: Does Harvard violate Title IX by discriminating against Asian Americans? Do these schools fail to use race-neutral alternatives? Do they use race as more than just a factor to boost applicants?
Lower court decisions upheld the precedent supporting race-conscious admissions, yet the Supreme Court changed tack. In a decision that Judge Ketanji Brown Jackson described as defying “law, history, logic, and justice,” the court cited that there was no compelling interest to continue affirmative action (considering diversity only a “commendable goal”), claimed that affirmative action relied on racial stereotypes, and that there was no clear end in time for affirmative action as described in the past.
Epperson clearly described what colleges may and may not do in the wake of this decision, and factors the court did not address. Colleges may design their missions as they see fit, and they may include qualities from student experiences based on race. The decision did not address scholarships, financial aid, recruitment, retention, pathway programs, employment, or DEIA programs — only admissions. It also does not affect employment, which is covered by Title VII of the Civil Rights Act.
Additionally, colleges are still allowed other forms of affirmative action that universities use to shape their student population. Legacy admissions are still legal, and often biased towards white students; for example, Princeton legacy applicants have nearly a 30% success rate in admissions, while everyone else has a less than 5% shot. Similarly, colleges are allowed to consider major donors, demographic/regional preferences, socioeconomic status, and athletes. Shockingly, only 11% of athletes would be admitted without this bonus factor in their favor.
In the wake of this decision, SFFA is instigating further litigation, including a challenge to a prestigious high school magnet program focused on diversity, to fellowship and grant programs aimed at increasing diversity, and to West Point (because the original court decision didn’t apply to military academies). Epperson also highlighted ongoing efforts to counter these efforts and increase diversity in university admissions: targeted recruitment and retention, a more holistic admissions process, elimination of other forms of affirmative action (e.g., legacy), elimination of college entrance exam requirements, and legislation to further diversity.
Press Conference: High-Energy Universe (by Mark Popinchalk)
It’s the last day of AAS, and while attendees might have low energy, this press conference was full of high-energy (astrophysics)!
Evidence of a Relic Active Galactic Nucleus Eruption (Press release)
The press conference started with Kimberly Weaver (NASA Goddard SFC) telling us how XMM Newton found a relic of an eruption from an active galaxy! Active galactic nuclei (AGN) are the centers of galaxies with a supermassive black hole accreting a hot disk of material. This produces lots of energy, and it can even produce high-powered jets, such as the AGN in Messier 87.
The team wanted to understand how AGN may affect star formation and power galactic outflows. All this high energy and moving matter should have a significant effect on galaxy evolution, and it was expected that one could trace previous nuclear activity.
So the researchers used ESA’s XMM Newton to look at NGC 4945. NGC 4945 is a spiral galaxy, also classified as a starburst due to its recent star formation. XMM has high sensitivity and a wide field of view. With just one observation they could image the entire galaxy.
Using their data, they saw that high-energy X-rays were outlining a huge clump of cold gas, 32,000 light-years long! But there were clearly some things in the way of the gas, such as individual stars and the light from the AGN itself. So they took further images using NASA’s Chandra X-ray Observatory. Using these observations they could remove the intervening features and still see a huge amount of cold gas.
A slide from the press conference of Kimberly Weaver showing cold gas in a distant galaxy.
The gas lined up with other observations suggesting a strong collimated outflow of material. The team thinks that 5 million years ago, jets from the AGN weren’t aimed out into space like they are in Messier 87, but instead smashed into the rest of the galaxy! Theory says that once they smash into the thing, the jets then disappear. So what we have leftover is a relic signature of how the jet drove in and left behind the cold gas clouds as a fossil of that activity.
Unveiling the Most Promising Formation Channel of Fast Radio Bursts Using Local Universe Bursts (Press release)
Next up were Aaron Pearlman (McGill University) and Mohit Bhardwaj (Carnegie Mellon University), who were presenting the evidence for a potential dominant formation channel of fast radio bursts (FRBs). FRBs are bright radio pulses of millisecond duration. What causes them is unknown, but the source must be very powerful, as the signals travel between galaxies. We know this because as radio waves move through intervening material, the signal disperses, and the amount of dispersion in FRB signals implies that they come from outside the galaxy.
But what causes them? And can there be multiple formation channels? The researchers used the CHIME radio telescope. Using it, they are able to find roughly 100 new FRBs per month. Using the telescope they can identify the location of the FRBs within 1 arcmin.
Using their previous database, they associated four of the FRBs to nearby spiral galaxies. Then they looked at other local-universe FRB sources that were associated with a galaxy, and saw that the sources are spiral galaxies.
Now that they had spiral galaxies as a clue, they could rule out many of the proposed formation methods. Globular clusters as a source was out, as we would see them from elliptical galaxies too. Certain stellar interactions? No way, otherwise it wouldn’t just be spirals either. Since they were all coming from spirals, they think this means it has to be one thing and one thing only: core collapse supernovae.
A slide from the press conference of Aaron Pearlman and Mohit Bhardwaj showing potential origins of fast radio bursts.
The prevalence of spiral hosts in the local universe is a major clue for FRBs, but it doesn’t answer everything. For example, we know of repeating FRBs — how does a supernova happen twice!
Evidence for Large-Scale Anisotropy in the Gamma-ray Sky (Press release)
Next up was Alexander Kashlinsky (NASA Goddard SFC), who had a real mystery to share with us all, about the distribution of gamma-ray radiation in the universe.
To start, there is a well-documented and studied dipole distribution in the cosmic microwave background radiation. In other words, there seems to be a preferred direction to it. There shouldn’t really be, but one possible explanation is that it could be due to the motion of the solar system making it appear that way.
If the CMD dipole is simply due to the solar system’s motion, then it should be detectable in gamma-ray radiation, too. If it isn’t, then it could have a potential cosmological implication.
Kashlinsky intended to probe for the dipole moment of the gamma-ray sky using Fermi LAT observations. Gamma rays are not microwaves, and due to relativistic effects they expected any dipole to be a bit higher in amplitude than that of the CMB.
However, what they measured was a gamma-ray dipole 10 times greater in amplitude than the CMB! They checked to see if the same is true for ultra-high-energy cosmic rays and found a similar dipole. They thought that maybe the ultra-high-energy cosmic rays are causing the gamma-ray dipole when they cascade and decay, but after looking at how that energy would be dissipated, it doesn’t make sense.
A slide from the press conference of Alexander Kashlinsky showing the location of the bizarre gamma-ray dipole.
Instead, it may be possible that the ultra-high-energy cosmic rays and the gamma rays come from the same source. So this co-emission of both ultra-high-energy cosmic rays and gamma rays seems to be coming from a yet unknown source!
Astronomers Find Spark of Star Birth Across Billions of Years (Press release)
Finally, Michael Calzadilla (MIT) asked the room how we arrived at the galaxies that we see today. Galaxies that we see today are either elliptical, sometimes called “red and dead,” while others are star-forming spirals. How do galaxies acquire the gas needed for star formation? Gas comes in and out of galaxies, and when the thermodynamics is right, stars can form. This atmospheric cooling has been known for the last 2 billion years and shown to be important for modern galaxies, but what about the past?
Well, the past was different! The peak of cosmic star formation was in the past, as well as galaxy mergers and black hole accretion, all peaking in the last 7–11 billion years. The challenge has been to find distant clusters and get multiwavelength follow up to understand their star formation.
The team used a well studied SPT-Chandra sample, which consists of an unbiased sample of 95 galaxy clusters spanning 10 billion years in evolution and that already had multiwavelength follow up.
A screenshot of the press conference of Michael Calzadilla discussing the atmosphere needed for star formation in galaxies.
They showed that the necessary thermodynamic conditions to trigger star formation that exist in the most recent 2 billion years are also needed back to 10 billion years ago too. So, it seems like making stars is still pretty similar! However, they found that the black hole feedback that regulates star formation in the current universe might not be doing the same thing in the past.
Perhaps a topic for a press conference at a future AAS!
Plenary Lecture: New Views of Dust and Star Formation in Nearby Galaxies with JWST, Karin Sandstrom (University of California, San Diego) (by William Lamb)
JWST is the gift that keeps on giving. It’s revolutionising astrophysics, cosmology, and our view of the universe. In this plenary, Karin Sandstrom offered attendees a snapshot of the incredible science that is being conducted with JWST after only 1.5 years of science operation.
Before JWST, there were some outlying questions regarding the baryon cycle: the flow of gas and dust from the interstellar medium onto galaxies that fuels star formation, which then causes the expulsion of material via outflows from the galaxy back into the interstellar medium. Those questions include what controls the gas reservoir for star formation and what controls the efficiency of star formation?
Previously, we had limited techniques to trace the interstellar medium and stellar formation, but with the telescope’s resolution and sensitivity to the near- and mid-infrared spectrum, this is no longer an issue. For example, Dr. Sandstrom attempted to get the audience excited about polycyclic aromatic hydrocarbons (PAHs), which are large carbonaceous molecules. The infrared emission from PAHs is strongly correlated with the presence of the interstellar medium. Thus, this makes PAHs a high-resolution tracer, which means by detecting PAHs, you detect where the interstellar medium is and where it is flowing. JWST’s light filters were designed to capture the emission from PAHs, hence JWST can create high-resolution maps of the interstellar medium in our Local Group. With this new map, we can compare simulations of galaxy formation to high-quality data to improve our models, and further refine our models of stellar formation.
And of course, Sandstrom just had to share some of the stunning images from JWST’s remarkable instrumentation…
Sandstrom presenting an image of NGC 628 as taken by JWST.
Press Conference: Oddities in the Sky (by Isabella Trierweiler)
True to its name, this session included a variety of puzzling phenomena that challenge our current astronomical models!
A Big Ring on the Sky: Alexia Lopez (Jeremiah Horrocks Institute – University of Central Lancashire) (Press release)
The standard model describes our best understanding of cosmology in our universe, and it hinges on a critical assumption, that the structure of our universe is isotropic and homogeneous on the largest scales. Verifying the assumption of homogeneity is really important; we currently estimate that the scale of homogeneity is about 1.2 billion light-years. In other words, the universe should not have any overarching structures that are larger than this scale. However, two years ago Lopez presented one large-scale structure that challenges homogeneity (the “Giant Arc”), and today she presented a second such structure called the “Big Ring.” The two structures are 3.3 billion and 1.3 billion light-years across, respectively.
To find these structures, Lopez uses the light from distant quasars to identify clumps of intervening matter. From the quasar mapping, she can construct a 3D map of intervening large-scale structure, with locations based on the dimmed quasars and distances extrapolated from Mg II absorption. Both of the identified structures are curiously about 9.2 billion light-years away, and they are quite close together on the sky. However, it’s unclear if this is a sign of a larger trend in the distribution of large scale structures. If these structures are proof that our current standard model for cosmology is insufficient, some options for improving our model include invoking cosmic strings, which may construct large scale structures, or assuming a “conformal cyclic cosmology” in which we are living in an infinite cycle of universes, resulting in the creation of circular structures. Lopez plans to continue her quasar analysis to get a better idea of how common these homogeneity-breaking structures might be.
A Potentially Isolated Quiescent Dwarf Galaxy: Timothy Carleton (Arizona State University)
Carleton presented an odd galaxy that was fortuitously observed by the PEARLS project, an extragalactic survey using JWST. He noticed the galaxy (called PEARLSDG) in the PEARLS images due to its odd appearance relative to the other nearby galaxies, which were the original targets of the survey. PEARLSDG is a dwarf galaxy imaged in remarkable detail — JWST was actually able to resolve individual stars in the galaxy! While most dwarf galaxies imaged by PEARLS and other projects are either young and isolated or old with a massive companion, PEARLSDG sticks out as an old, isolated galaxy. How old and isolated galaxies form remains an open question, and Carleton says further spectroscopy of the galaxy will help characterize it and hopefully shed more light on how it formed.
Timothy Carleton presents JWST observations of a potential isolated dwarf galaxy.
Close Encounters of the Supermassive Black Hole Kind: Tidal Disruption Events and What They Can Reveal About Black Holes and Stars in Distant Galaxies: Ananya Bandopadhyay (Syracuse University) (Press release)
Supermassive black holes (SMBHs) are intriguing objects that are generally very difficult to study as they do not emit light. Because of this, tidal disruption events (TDEs) are especially valuable events, providing some insight into the properties of the SMBH. TDEs occur when a star approaches a SMBH and is disrupted by the strong tidal forces around the black hole. The disruption and accretion of the star in turn spark a flare whose light curve we can measure. TDEs are relatively rare, and we know of about a hundred of these events so far. The typical pattern for a TDE light curve is a rise in brightness over a 30–50 day period, followed by a gradual tapering off period. The main question in this work is what determines the peak luminosity and the timescale of this light curve.
We typically use analytical approximations to recreate the shape of the light curves, but Bandopadhyay demonstrated that the generally accepted analytical model for TDEs results in a very different light curve relative to detailed hydrodynamical simulations, motivating the need for a new model. She presented an updated model for TDE light curves in which she demonstrated that the timing of the peak in the light curve is actually independent of the mass of the accreted star, remaining at ~50 days across the board, while the peak luminosity of the TDE scales with the stellar mass. One of the implications of this finding is that TDEs that are energetic enough to cause jets around the SMBH are likely related to the disruptions of high-mass stars.
Impressively, much of the work of the project was completed by high school students! Syracuse University hosts a summer research program, and their student interns worked on the numerical simulations for the TDEs and are co-authors for this work.
Zooniverse People-Powered Research Platform Reaches New Milestones: Laura Trouille (The Adler Planetarium; Zooniverse)
Zooniverse is the largest platform available for citizen science, with over 2.6 million participants around the world. It was started in 2007 through the founding of the GalaxyZoo project, in which members of the public helped classify different galaxy images. The platform grew rapidly, particularly after 2015 when a DIY project builder was added so that any researcher could easily create their own project. Laura shared that currently 40–50 new projects are added every year! Between the large user base and integrated machine learning algorithms, Zooniverse is a very powerful tool for analyzing large datasets and has led to over 400 scientific publications, often with citizen scientists included as co-authors.
Trouille noted a few recent results from Zooniverse projects. Having so many different eyes on the data makes Zooniverse especially good at identifying unusual features that would typically escape notice in simple coded pipelines. In the past few weeks, the project “Planet Hunters TESS” discovered a habitable-zone planet while the “Backyard Worlds” team identified an aurora on a brown dwarf! To date, citizen science users have contributed 1.6 million hours of work to Zooniverse projects, the equivalent of nearly 800 full-time workers.
If you’d like to contribute as a citizen scientist, getting involved is super easy! Consider joining the gamma-ray bursts team, or hunt for asteroids with the Daily Minor Planet group. And if you’re a scientist who would like to start your own project, definitely do reach out to Trouille and her team.
Dannie Heineman Prize Lecture: Small Bodies: Primitive Witnesses to the Birth of a Habitable Solar System, Karen Meech (University of Hawaiʻi) (by Yoni Brande)
Karen Meech, the winner of the 2023 Dannie Heineman Prize for Astrophysics, has spent her career studying small bodies (like comets and asteroids) in the solar system. Her prize lecture today focused on how observations of these bodies can teach us about how both our own solar system evolved and how extrasolar planetary systems may be able to develop habitability.
Our current understanding of the development of life says that habitability needs liquid water, organic energy sources, and rocky planets. No currently known extrasolar planetary systems meet these criteria, so we need to know whether the conditions in our solar system are unique.
A common refrain in astrobiology is “follow the water” — that is, understand where water is in a system and how it moves around, and then we should be able to predict where life might arise. In order to study the water content of the early solar system, astrobiologists like Meech and collaborators use remote observations as well as direct analysis of samples of comets and asteroids, which are cosmic detritus left over from those early eras. Meech showed a short review of this history, showing that within a few hundred million years of Earth’s formation, it already had liquid water oceans. The main question, then, is how the water got here.
One theory says that icy bodies from the outer reaches of the solar system were gravitationally scattered to the inner solar system and eventually impacted Earth. This cometary water then became the main reservoir. To test this, we can look at the ratio of deuterium to hydrogen (D/H). The D/H ratio of the early solar system is low near the Sun and increases with distance from the Sun, making it a good tracer of formation location. Earth’s D/H value is significantly elevated for its current position, which is a point in favor of the icy body delivery theory. If high D/H comets swung by Earth and dropped off their water, that could increase Earth’s D/H ratio. However, the last few decades of observations have shown mixed D/H results for different small bodies, and Meech stressed that we really don’t fully understand these primordial isotopic ratios, or if they are even meaningful in studying these formation and evolution processes.
Ultimately, Meech says, water probably comes from multiple sources — we just need to figure out which sources and when. Planet formation is complex, with many chemical and dynamical processes jumbling up the possible tracers of this history. A newly observed kind of comet may finally untangle some of this historical web.
Long-period, tailless comets called “Manxes” (named after the cat) show spectra similar to inner-solar system rocky asteroids. Meech and collaborators’ studies of Manxes show they may have a complex history. They likely began their lives as normal main-belt asteroids (hence the similar spectra), but were dynamically scattered out to the Oort Cloud, and then scattered back into the inner solar system on comet-like orbits. They appear to have a range of surface colors, which could be evidence of diverse formation locations across the solar system.
Meech concluded with some final thoughts: the study of Earth’s water is interdisciplinary, merging expertise from astronomy, planetary science, geology, and more. We need a better understanding of the chemical and dynamical history of our solar system, and in order to obtain that we need in-situ explorations of solar system planets, small bodies, and even interstellar interlopers like ʻOumuamua. These topics have far-reaching implications for habitability and the origin of life. If the solar system is not representative of planetary systems in general, and if the conditions here are special, we can’t assume all other potentially habitable systems will have them as well.
Berkeley Prize Lecture: Exploring Our Transient Universe In All Colors, Wen-fai Fong (Northwestern University) (by Pratik Gandhi)
Wen-fai Fong, while receiving the Berkeley Prize, remarked that the award is important to her because it recognizes not only her work but also that of her amazing research group. Throughout her plenary talk, she highlighted the work of her graduate students, postdocs, and external collaborators. Fong likes to study astronomical “transients,” or phenomena that are time-varying, using the technique of multi-messenger astronomy — probing these phenomena using observations across the entire electromagnetic spectrum from radio waves to gamma rays, and also using gravitational waves. As she remarked, “the universe varies on remarkably human timescales,” and she derives great joy from observing it in all its variety of colors.
Speaking of colors, Fong highlighted three key themes throughout her talk: (1) Teamwork, which she discussed as being crucial for the kind of fast-paced, time-sensitive research required in transient astronomy, (2) the importance of color, in terms of leveraging the entire electromagnetic spectrum, and (3) that timing is everything, especially in the discipline that she and her group specialize in.
In terms of why the study of transients is important, Fong mentioned that they are often the birthplaces of numerous heavy elements, laboratories for studying extreme physics, the sources of gravitational waves, and probes of otherwise invisible material that we wouldn’t have noticed otherwise. The sources of transients are often the formation of the three classes of compact objects: white dwarfs (WDs), neutron stars (NSs), and black holes (BHs). These compact objects are all the end stages of the life cycles of stars of different masses, with NSs and BHs occurring as a result of massive stars going supernova (which happen to be the most common transients).
Gamma-ray bursts (GRBs)
Fong mentioned how GRBs were first discovered in the 1960s, after which NASA developed multiple gamma-ray observatories in space. Thousands of GRBs have been detected to date, and they are usually extragalactic in origin. GRBs come in two populations (long and short), with short GRBs occurring during NS-NS mergers and long GRBs happening during the collapse of massive stars. Her group focuses mainly on short GRBs; the first evidence for which was the 2017 discovery of gravitational waves from a NS-NS merger followed by a GRB. Short GRBs have been detected in galaxies out to redshifts of z ~ 2!
Fong highlighted how when GRBs are detected (by the Swift telescope, for example), her phone will ping with notifications. Time is of the essence, because they have to mobilize multiple telescopes across the spectrum immediately. Right before Thanksgiving 2023 there was a GRB that was detected, and it was only through the amazing teamwork of her group that they were able to mobilize multiple telescopes and get memos (“circulars”) out to the transients community!
Questions that the Fong group is trying to address concerning GRBs include the following: What do two NSs create? How and where are heavy elements created? What conditions are required to produce these rare transients? The afterglow radiation that produces the GRBs gives us a handle on burst energetics. The NS-NS merger itself tells us about the mass of heavy elements produced. Finally, her group is working on building the BRIGHT repository, a catalog of galaxies that host GRBs, to try to understand the conditions required for them to occur.
Fast radio bursts (FRBs)
Fong also highlighted a second kind of transient, which has only recently been discovered. In 2007, a serendipitous discovery sparked the fast radio burst (FRB) revolution. FRBs are milliseconds-long bright radio pulses similar to GRBs but on the radio side of the spectrum. Some FRBs repeat periodically while others do not, and the cause of this difference is still unknown! Leading hypotheses for the sources of FRBs include magnetars, or extremely magnetized neutron stars. The Fong group is part of the “Fast and Fortunate FRB Follow-up” (F4) collaboration, which mobilizes telescopes across the electromagnetic spectrum, from ALMA to Chandra, in order to also look at the host galaxies of the FRBs.
Fong concluded the talk by returning to the importance of teamwork, color, and timing, and saying, “There is incredible momentum behind this field and the era of 1,000+ hosts is not far away — we’re thrilled; we’re excited; we’re scared!”
Editor’s Note: This week we’re at the 243rd AAS meeting in New Orleans, LA. 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 January 16th.
Henry Norris Russell Lectureship: Frank Shu’s Legacy in Unraveling Star Formation, Susana Lizano (Instituto De Radioastronomia Y Astrofisica) (by Ivey Davis)
Frank Shu was a titan of astrophysical fluid dynamics theory, with his work being seminal to our understanding of star and planet formation, protoplanetary (and planetary) disk structure, galactic spiral arm formation and stability, and nigh countless other topics across essentially all fields in astrophysics. He was awarded the Henry Norris Russell Lectureship before his passing in April of 2023. Upon being awarded the Lectureship, he not only requested that Susana Lizano give this lecture on his behalf, but also donated the associated money back to the AAS. In honor of Shu’s contribution to astrophysical fluid dynamics, and astronomy as a whole, Lizano gave an overview of Shu’s career, which in a way is an overview of the field of star formation theory.
Shu’s first work was addressing the spiral structure of galaxies by treating them as density waves propagating through a disk, rather than as fixed, physical structures as had originally been assumed. This new framework solved the winding problem that had arisen in the fixed-structure framework, as well as addressed other galactic features like color gradients and the locations of OB star associations. Similar density-wave treatments would later be applied to other places we see disks, such as in Saturn’s rings and in the material around young or forming stars.
In 1977, Shu published his work on the collapse of spheres of gas as a way to explain core formation and subsequent star formation. A decade later, he, along with Lizano and Fred Adams, would publish the review that is still used as the star formation paradigm, showing how pressure, temperature, and density evolve with time to eventually form young stellar objects from molecular gas clouds and also explains the onset of the Hayashi track. Expansions of this work to rigorously analyze the effects of magnetic fields and rotation on gaseous bodies, both by Shu and by others, would go on to explain or elaborate on evolutionary sequences from protostars to main-sequence stars, the scale height and aspect ratio of accretion disks, disk formation conditions, planetary migration, planetesimal formation, and so much more.
Shu was an active researcher and astronomical community member, serving as president of the AAS from 1994 to 1996, and most recently was investigating technologies to help combat the climate crisis. Questions following Lizano’s talk not only included questions about what the future of the field looked like, but also recountings of individuals’ personal experiences with Shu. This lecture was a truly heartfelt tribute to a dedicated astronomer and mentor.
Press Conference: Supernovae and Stars (by Mark Popinchalk)
This press conference was all about stars going supernova! (Except for one result about galactic gas that was shuffled into the session due to a missed flight.)
A 12.4-Day Periodicity in a Close Binary System After a Supernova (Press release)
First, Ping Chen (Weizmann Institute of Science) shared a peculiar system with us. You can measure the kind of light a supernova gives off to see what elements are in it. It may have some hydrogen, or helium, or neither. This is often thought to be due to what the outer layers of the star were doing before the explosion. The dense core will stay put, but the outer layers of hydrogen or helium may or may not get stripped off. Whether this stripping always occurs, and how it happens, is hotly debated.
The case of the supernova SN 2022jli is especially weird. Its brightness shows a periodic dimming and brightening on a 12.4-day period, which is already unique. It becomes even more interesting that the spectra of the supernova usually doesn’t show hydrogen, except for particular points in the 12.4-day period!
A six-panel slide from Ping Chen’s talk showing the orbital interactions of the compact supernova survivor and its binary companion.
The story appears to be that there were two stars in a binary system, one that went supernova and is now a compact object, and the other a star in an elliptical orbit around the remnant. When the outer star approaches the remnant on its orbit, the remnant strips some hydrogen from the outer star and the extra hydrogen is added to the remnant’s spectra. The outer star has to be on an elliptical orbit so that the stripping only occurs at certain points during the star’s orbit.
Interesting!
Rare Insight Into the Origins of Type Ia Supernovae Progenitors From a Double Detonation (Press release)
Estefania Padilla Gonzalez (UC Santa Barbara and Las Cumbres Observatory) introduced the audience to a great candidate for a double detonation Type Ia supernova. She started by introducing us all to Type Ia supernovae. They have predictive luminosity, which is to say that the light from their explosions are understood really well, and they have been used as “standard candles” to enable distance measurements to other galaxies.
Even though they are well understood, there are still some questions on how Type Ia supernovae explode. The common understanding is that to have a Type Ia supernova you need a white dwarf that is under 1.4 solar masses, the Chandrasekhar limit. Then you need another nearby star to feed mass onto the white dwarf until it crosses that limit, and boom! Supernova!
However, there may be sub-Chandrasekhar-mass explosions. Their occurrence is not currently supported by observations, but they are theoretically possible. How can we get the smaller stars to explode? The idea is that the helium layer surrounding the core of the star starts to ignite early, which causes a shock wave that travels around the star. When the shock waves meet each other, that provides even more force that could trigger the rest of the core to go full supernova.
Summary slide from Estefania Padilla Gonzalez’s talk.
And that’s where the team’s research comes in! SN 2022joj is a Type Ia supernova that has a few different characteristics, a non-standard candle. For example, there is suppression in the blue wavelengths of the light it emits, which might be due to helium ash absorption at those wavelengths. However, once the full explosion occurs, the end result looks like a regular Type I supernova.
It’s an exciting candidate for a double detonation of a thin helium shell!
Periodic Eruptions of a Supernova Impostor
Mojgan Aghakhanloo (University of Virginia) was next, and had an intriguing system, an impostor supernova! SN 2000ch is the impostor in question, and it’s thought to be an evolved massive star that has undergone non-terminal eruptions. What does that mean? It’s a big star that’s not dead yet. Eta Carinae is a great example that some might be familiar with — huge outer layers barely contained in its gravity influence, a star that is just clinging to life. It went through a “Great Eruption” in the past.
SN 2000ch is having an even worse time. Since 2000, it’s had 23 different eruptions, and the team has shown that there is an interesting periodicity to it, that the eruptions occur approximately every 200.7 ± 2 days. What’s the cause? It’s probably another binary system!
A summary slide from Mojgan Aghakhanloo’s talk showing the binary orbit interacting with the outer layer of the massive star.
The big evolved star is not by itself and has a secondary companion in the system, orbiting around it. As the other star gets close, it passes through the outer layers, causing eruptions. And since the layers are so extended, it is likely that the material the path goes through changes, explaining why some eruptions are bigger than others.
These eruptions look just like those that Eta Carinae went through, and makes this a target of “great interest.” The next eruption is likely in March of this year!
Spectacular Nucleosynthesis from Early Massive Stars (Press release)
Alexander Ji (University of Chicago) brought us a really interesting story, a star with such a bizarre composition, that it likely formed from the supernova of a really big star! That’s right: learning about an older star by looking at a current one.
SDSS is a huge survey mission that is “lawn-mowering the sky” taking spectra of stars. It discovered a star with spectacular composition. J0931, an old star, has unusually low magnesium abundance for its metallicity, and was flagged for follow up by the Magellan telescope. The additional observation showed that it also had strangely low amounts of sodium, and tons of strontium.
What does that all mean? Well, if they trace back to when the star is likely to have formed (~10 billion years ago), it must have come from a peculiar cloud of material to have these kinds of elemental ratios. These kinds of elements only form when a star goes supernova, and when compared to theoretical models of the kind of star that would need to go supernova to make that peculiar cloud, (to form the smaller star that exists today) it would have to be massive.
A slide from Alexander Ji’s talk showing the progenitor supernova star before the next star.
So massive, that it would have to be > 50 times the mass of our Sun, even up to 80 solar masses. The challenge is that no model fits all the element ratios they find, and most models predict that stars that big shouldn’t even go supernova! A star that big should collapse directly into a black hole. The presence of this star shows that the existing supernova models are too simple, and that this particular star is a blockbuster.
They’ve given it a special name since they were working on it this summer: The Barbenheimer Star : )
The Nuclear Outflow from the Milky Way (Press release)
Last but not least was Jay Lockman (Green Bank Telescope), who had finally made it to AAS after flight troubles and was given a chance to speak at this press conference rather than the one he missed.
He pointed out that when we look at most large galaxies, they have bursts of energy in their cores that drive winds which carry mass out from the galaxy center. There is data to suggest a similar effect is happening in the Milky Way, but it is hard to see since we are in the plane of the disk. However, there are new observations that show that cold hydrogen clouds are being pushed by the hot wind from black holes or starbursts in the center of our galaxy.
A summary slide from Jay Lockman showing gas clouds shot out of the Milky Way.
A good analogy would be that the forces pushing from the center of the galaxy are an astrophysical mixture of a snow blower and a leaf blower! The movement of the gas is in straight lines out from the source and then spreads out, which is what a snow blower does. However the gas is being pushed around like leaves by a leaf blower. An autumnal/winter analogy!
The team has been attempting to locate over 300 clouds with the Green Bank Telescope. The flows are coming out in two cone shapes, at high velocities, with some clouds approaching the escape velocity of the Milky Way. They likely won’t escape, but it shows that the forces can certainly launch material around the galaxy!
Annie Jump Cannon Prize Lecture: Marta Bryan (University of Toronto) (by Ali Crisp)
In her lecture, 2023 Annie Jump Cannon Prize award winner Marta Bryan led us through her research on the dynamics of giant exoplanets and how dynamics can provide insight into the formation mechanisms of giant planets, their impacts on other planets in their systems, and even how they affect the potential habitability of a system.
To begin, she briefly explained what planetary properties we can learn from more “traditional” exoplanet studies using the radial velocity and transit techniques: the mass of the planet from radial velocity measurements, the radius of the planet from transit detections, and the orbital period, inclination, and eccentricity from either. She then adds that with new atmospheric detections, you can get information about the composition, spin, planetary obliquity, and weather on a giant planet.
But what does combining all these properties tell us? For one thing, characterizing planetary spin and comparing it to the host star’s spin can give us information about how the planet and star formed. In a perfect system, the spin of the star and planet would be aligned, and their equators would be parallel. However, we see even in our own system that this isn’t the case. Uranus, for instance, is tilted on its axis 98 degrees relative to the equator of the Sun, and Venus spins in the opposite direction from all the other planets. Constraining the orbital dynamics of exoplanets and finding any misalignments or spin oddities can indicate some sort of gravitational interaction occurred. In systems with close-in super-Earths and far-out giant planets, these suggested interactions could indicate that the giant planet caused misalignments or spin changes through, e.g., migration during its formation.
Bryan ends by contextualizing her observations and constraints in the search for biosignatures. As the number of confirmed exoplanets increases, it becomes impossible for us to characterize all their atmospheres. Since we know our own solar system hosts life and contains both close-in terrestrial planets and far-out gas giants, we could prioritize observations of similar systems for biosignatures and hopefully help constrain what constitutes habitability.
This session provided new insights into a variety of planetary systems and included two projects led by undergraduate students!
Stellar Paternity Tests: Matching High-Latitude B Stars to the Open Clusters of Their Birth (Press release)
Brandon Schweers and Ginny McSwain (Lehigh University)
Star formation in the Milky Way is generally believed to be restricted to the thin disk of the galaxy. However, there is an interesting population of B-type stars that have been observed far outside of the thin disk. Brandon Schweers, an undergrad at Lehigh University, sought to trace back the trajectories of these so-called “orphan” B stars to figure out whether they did indeed form in the thin disk and migrated away from home, or whether they represent a different pathway for star formation.
Schweers used kinematic data from Gaia to reconstruct the trajectories for stars in and around clusters over the past 30 million years. They then used those trajectories to see whether orphaned stars ever crossed paths with a potential “parent” cluster. Overall, Schweers found 22 intersections between orphan stars and parent clusters, with some stars intersecting multiple clusters. To validate whether the paired orphans and parents were indeed related, Schweers constructed color–magnitude diagrams for the parent clusters and checked whether the orphaned stars fell within the cluster’s parameter space. From this analysis, Schweers found 15 matches between orphan stars and parent clusters and was able to estimate the times at which the stars were originally ejected from their host clusters, as well as the initial velocities at the time of ejection. Based on the ejection velocities, Schweers found that one star was ejected due to a very energetic event, like a supernova, while the rest were likely ejected due to dynamical interactions with their parent cluster. Interestingly, a few orphan stars never intersected with any clusters, bringing up the question of whether there may be some star formation going on above and below the thin disk after all.
Weakened Magnetic Braking in the Exoplanet Host Star 51 Pegasi (Press release)
Travis Metcalfe (White Dwarf Research Corporation)
51 Pegasi (51 Peg) is one of the most famous stars in exoplanet science, as it hosts the first exoplanet astronomers ever discovered around a main-sequence star. Despite its planet being so well known, Travis Metcalfe showed that there is still more to learn about 51 Peg from its magnetic field structure. 51 Peg is a Sun-like star, which means it was likely born with a rapid spin and eventually slowed down as it shed angular momentum. The main mechanism for slowing rotation in a young star is called magnetic braking, where angular momentum is carried away by stellar winds, and the rate of the loss of angular momentum is depending on both the strength and complexity of the magnetic field around the star.
To map the magnetic field structure around 51 Peg, Metcalfe used data from the Large Binocular Telescope to first map the magnetic surface of the star and then reconstruct the magnetic field lines. Interestingly, he found that 51 Peg follows an unusual trend in magnetic braking where young, rapidly rotating stars have relatively strong braking, and then somewhat suddenly fall to a weakened braking state as they age. While the source of the drop is not entirely clear, it may have to do with changes in the complexity of the magnetic field structure around the aging stars. The Sun seems to have gone through this drop in braking as well, and curiously the timing of the drop in magnetic braking corresponds to emergence of land-based life on Earth, raising the question of how magnetic evolution of host stars and planet habitability may be intertwined.
JWST’s New View of Beta Pictoris Suggests Recent Episodic Dust Production from an Eccentric, Inclined Secondary Debris Disk (Press release 1, press release 2)
Christopher Stark (NASA Goddard)
Beta Pictoris is another well-known exoplanet system, remarkable both because its two known exoplanets reside in a debris disk and because it has shown evidence of exo-comets. Beta Pictoris’s debris disk has been a point of interest for decades, and more recently it was shown to have two components: an edge-on main disk and a somewhat warped secondary disk with interesting CO emissions. The complexity doesn’t stop there though; using NIRCam and MIRI data, Christopher Stark showed that even more features are hidden in Beta Pictoris’s disk!
The new MIRI images show a fork, an elongated feature (named the “cat’s tail”), and several shorter nebulous features. The data show that these features are connected to the secondary disk of Beta Pictoris, and that the material of the secondary disk appears to be different both in temperature and in composition from the main disk. Stark says the secondary disk material seems to be consistent with fluffy, organic, refractory material, not unlike the samples obtained by OSIRIS-REx. As far as the origins of the cat tail and other features, the most likely explanation is that they are the tails left by collisions within the debris belt. Stark showed that such a collision would need to occur in about the last 150 years to create the observed features, and furthermore that the shape of the cat tail is consistent with the same organic, refractory material extrapolated from the MIRI data. To complete the picture, the 150-year estimated timescale fits nicely with the observed CO emission. CO dissociates in about 150 years, so the observed CO would have been created relatively recently, and the collision that created the cat tail is a perfect candidate for emitting CO into the disk! Stark noted that in addition to providing more insight into the Beta Pictoris disk, these observations prove that debris disks could be a lot more active than we previously thought and should definitely be further investigated using JWST.
How Do Ultra-Massive Planets Form? Gaining New Insight by Measuring the Orbital Tilt of a Rare Transiting Brown Dwarf (Press release)
Steven Giacalone (Caltech)
Thus far, planets have been observed at a huge range of size scales, from our terrestrial planets up to Jupiter masses. However, there’s currently a gap between objects of Jupiter mass and low-mass stars. The few ultra-massive planets / brown dwarfs in this gap are intriguing objects, and their origins are an ongoing question. There are generally two options for their formation: either they form like planets, accreting in disks around stars, or they form like binary stars and collapse directly from gas. So far, most of the brown dwarfs appear to have orbits and compositions that are consistent with star-like formation. However, Steven Giacalone has a new observation that brings planet-like formation back into the picture.
For this study, Giacalone measured the orbital tilt of a brown dwarf, GPX-1b. GPX-1b is 20 times more massive than Jupiter and resides quite close to its host star. The orbital tilt is related to the formation pathway because brown dwarfs that form as planets should be aligned with the spin of the host star (like the planets in our own solar system), while brown dwarfs that form similar to stars could have any orbital orientations. Giacalone used the Keck Planet Finder to observe the brown dwarf’s transit. To measure the orbital tilt, he analyzed the wiggles in the transit spectrum that arise from the transiting brown dwarf crossing first the blue-shifted and then red-shifted portions of the star’s surface. From this method, he found that the tilt is aligned with the star, indicating that GPX-1b likely formed as a planet. Brown dwarfs are relatively rare objects, so this was the first measurement of its kind, and it introduces interesting new evidence for brown dwarf formation!
An Earth-Sized Addition to a 400-Myr Planetary System in the Ursa Major Moving Group (Press release)
Alyssa Jankowski and Melinda Soares-Furtado (University of Wisconsin – Madison)
Young planets are really important to our understanding of planet formation, but they are generally very difficult to find and reliably date. Alyssa Jankowski, an undergraduate at the University of Wisconsin-Madison, leveraged the power of moving groups, or stars that all formed from a common molecular cloud, to better date planet ages and search for young systems. In particular, Jankowski studied the system HD 63433, which is part of a moving group that includes many stars in the Big Dipper. HD 63433 is a Sun-like star, but it’s only about 400 million years old (compared to our solar system’s 4.6-billion-year age).
Previous work on the system unveiled two sub-Neptune sized plants, both on very short orbits. However, using new TESS data, Jankowski identified a third, Earth-sized planet in the system! The new planet has an incredibly short period of only 4 days, and while it is interior to the two sub-Neptunes, the whole system still fits within the orbit of Mercury. As the new planet is so close to the host star, it is likely tidally locked, leading to day-side temperatures of 1500K and a likely lava hemisphere. The new planet is really intriguing and presents an interesting opportunity to study atmospheric loss, a common trademark of young planets. Jankowski says there are plans to re-observe the system with Hubble and JWST soon and check for any heavy-element outgassing.
Plenary Lecture: Investigating the Early Universe, Jamie Bock (California Institute of Technology) (by Isabella Trierweiler)
In his plenary lecture, Jamie Bock shared some exciting new insights into the early universe, along with the technological improvements that will help us probe this era in greater detail in the coming years. In particular, Dr. Bock is interested in inflation, the period of time when the universe grew exponentially. Inflation is especially difficult to study; it was an incredibly high-energy event, making it impossible to study through experimentation (the energy scale is 1016 GeV, whereas the Large Hadron Collider currently reaches about 104 GeV), and it was a period of time when the universe very quickly moved from quantum scales to large-scale structures, complicating any attempts at simulation or computation. Thus direct observations remain our most powerful tool in studying the early universe.
A map of temperature fluctuations in the cosmic microwave background from WMAP. This map shows temperature deviations of up to 200 microkelvin. [NASA / WMAP Science Team]
Since its discovery in 1964, the cosmic microwave background (CMB) has been our main means of studying inflation. The CMB is the earliest light we can detect, made up of the photons that come from the moment the universe cooled enough for light to pass freely through space. To first order, all parts of the CMB are the same temperature, 2.7K. This is strong evidence of inflation because it means all parts of the sky needed to have been in contact at one point before growing to its current size. However, very small fluctuations exist in the CMB, and it is these fluctuations that allow us to more precisely study inflation. The fluctuations are a result of inflation amplifying quantum fluctuations in the early universe, and we can work backwards from the fluctuations to characterize inflation.
To characterize the fluctuations, we collect all the information about the size and strength of the fluctuations into a plot called the power spectrum. The goal of the power spectrum is to understand whether temperatures in the CMB are more correlated at particular spatial scales than others. Constructing the power spectrum is somewhat complex, but you can roughly imagine picking two points on the sky at some set distance apart and checking whether their temperatures are the same, and then repeating this for every set of points on the sky at that same set distance, and then doing the whole thing again at all possible distances. The structure of the resulting plot determines parameters like the geometry of the universe and the density of matter and dark matter. Over the past few decades, we’ve been able to fill in more and more of the power spectrum, and we have now reached a point where further measurements are only limited by photon noise.
So far, the results are well in favor of inflation. However, the difficulty now is to come up with a specific model for how it occurred. Currently over 100 proposed models exist, conveniently packaged into this 777-page document. Dr. Bock says there are two main questions to address to narrow down the options: 1) Is there a primordial gravitational wave background, and 2) so far CMB statistics seem to be Gaussian, but is there a non-Gaussian component? The gravitational wave background would tell us the energy scale of inflation, while the non-Gaussian component would show whether a single decaying field or multiple fields were responsible for causing inflation. So far, the BICEP and Keck arrays have been used to measure CMB polarization, concluding that inflation does not proceed simply along a power law. Meanwhile, the upcoming SPHEREx mission is poised to start measuring patterns in large scale structure, looking for correlations in the geometries of the structure to answer the question of non-Gaussian components and further narrow down the set of potential inflation models.
Newton Lacey Pierce Prize Lecture: Characterizing the Properties of Accreting Neutron Stars Through X-ray Observations, Renee Ludlam (Wayne State University) (by Ivey Davis)
We’ve heard quite a bit about the power of pulsars in astrophysics through the lectures on Monday and Tuesday, but today, Renee Ludlam focuses more generally on neutron stars, the various ways they can exist, and what that can tell us about physics.
As mentioned in previous talks, neutron stars push the extremes of our understanding of physics since we can’t measure such conditions on Earth. They have extreme pressures, densities, and magnetic fields that we could (presumably) never hope to replicate on Earth. Such extremes push our understanding of physics, especially how we describe the radial profiles of density, pressure, and temperature, called equations of state (EOSs). Although we have many ideas for what the EOS of neutron stars might be, it’s difficult to constrain what the correct solution is without being able to identify both the mass and the radius of the neutron star.
Because neutron stars push our understanding of physics to such extremes, we don’t know which model of neutron star interiors is most accurate. In order to constrain this, it’s important to understand the neutron star’s mass (somewhat well constrained in binary systems) and radius (much harder to constrain). Ludlam uses NuSTAR and NICER observations of X-ray binaries in order to put constraints on neutron star radii. These are systems that include a neutron star in a binary system (usually) with a main-sequence star. The neutron star occasionally accretes material from its companion star and produces X-rays. Constraining a neutron star’s radius requires measuring properties of the accretion disk around the neutron star in such a binary. But, this in turn relies on making assumptions about the process responsible for making the accretion disk. By studying the observational properties of accretion onto neutron stars, and how it compares with our models of the accretion, we can start to make conclusions about the system as a whole, as well as about the properties of the individual neutron star.
By observing extreme systems like ultra-compact X-ray binaries, Ludlam has additional spectral lines to study the effects of accretion onto neutron stars, which has helped to further put constraints on neutron star radii. As we continue to observe the unique effects of accretion onto neutron stars, and the various ways that this accretion can occur, there should be more and more stringent constraints on the EOS for neutron stars, and therefore a more robust understanding of physics and how it operates in such extreme circumstances.
Editor’s Note: This week we’re at the 243rd AAS meeting in New Orleans, LA. 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 January 16th.
Plenary Lecture: Radio Astrophysics and Cosmology from the Moon, Jack Burns (University of Colorado, Boulder) (by Briley Lewis)
Day 2 started off with a science fiction dream becoming reality: putting telescopes on the far side of the Moon. Jack Burns, Professor Emeritus at University of Colorado, Boulder, detailed the actual plans to do so in this morning’s plenary. This isn’t a new idea — radio telescopes on the lunar far side were envisioned even before the Apollo 11 landing. Science fiction author Arthur C. Clarke (most famous for 2001: A Space Odyssey) at the time said, “In a few generations, all serious astronomy will be with telescopes on the Moon or in space.” Burns noted that “it has now been a few generations” and we have incredible space telescopes like JWST, leaving only the Moon part left to do.
What makes the lunar far side so appealing is that it’s uniquely radio quiet, with a dry and stable environment and no ionosphere to generate interference. There’s one particular signal radio astronomers and cosmologists want to chase: the well-known 21-centimeter line, which can act as a cosmological probe to explore the dark ages and reionization in the early days of the universe.
NASA is already going back to the Moon with its Artemis program, and its Commercial Lunar Payload Services initiative partners with private companies to deliver more scientific payloads to the Moon. One such project is Radio Wave Observations at the Lunar Surface of the Electron Sheath (ROLSES), which will fly aboard Intuitive Machines 1 in February. The experiment consists of telescoping antennas which will pop out in a spring-loaded system with a classic spectrometer, and will cover a wide frequency range to detect radio signals from a variety of astrophysical signals. It plans to land at the lunar south pole near Shackleton crater, setting the record for closest landing to the lunar south pole; the Indian Chandrayaan-3 probe recently landed 30 degrees away, and this project will only be 10 degrees away.
ROLSES has many science goals, including measuring the electron sheath created by interactions between solar wind and lunar regolith, which is expected to exist but hasn’t yet been measured. It’ll be observing the galactic radio spectrum, measuring the dielectric constant of the lunar subsurface, and — perhaps most importantly — proving that detecting radio signals from the lunar far side is possible, paving the way for future missions. Although ROLSES’ galactic observations won’t reach the pot of gold at the end of the rainbow (the 21-cm line background measurement), it will help characterize the radio emission of the galaxy, which needs to be known, so the Milky Way can be effectively removed from the foreground of future cosmological observations.
Looking further ahead, the LuSEE-Night mission will work on actually measuring that 21-cm line for cosmology purposes in 2025. In the even more distant future, the proposed FARSIDE project would set up an interferometric radio array on the Moon, and the ambitious Far View project would expand such an array to 100,000 dipole antennas, constructed from resources gathered in situ on the Moon.
Press Conference: Exoplanets and Brown Dwarfs (by Pratik Gandhi)
This press conference had four exciting presentations on brown dwarfs and exoplanets, collectively dubbed “other worlds,” by researchers from the American Museum of Natural History and University of California, Los Angeles!
Extrasolar Worlds Exhibit Exotic Sandy Clouds at the Equator
An example BD infrared spectrum from their sample is shown in the bottom right of this photo. The characteristic feature highlighted in red indicates the presence of sandy clouds in the BD atmosphere.
Kicking off the session was Genaro Suarez, a postdoc at the American Museum of Natural History (AMNH), and member of the Brown Dwarfs in New York City group (or BDNYC), who told us about how the equators of exoplanets are often cloudier than the poles! Brown dwarfs (BDs) are considered the link between the lowest-mass stars and gas giant planets — they have insufficient mass to carry out fusion and radiate like stars, but they often have a little too much mass to be considered “planets.” Suarez’s focus is on L-type BDs, which are the hottest category. Using archival data from the Spitzer Space Telescope (the precursor to JWST), they identified a feature in the spectra of BD atmospheres that is indicative of clouds that are composed mostly of sandy grains (see Figure 1)! Additionally, their team found a correlation between the inclination or viewing angle, cloud cover, and color of the BD atmosphere — all of which suggest that BDs have more sandy clouds along their equators than at their poles.
Using Citizen Science to Identify New Ultracool Benchmark Systems
The second talk of this press conference was by Austin Rothermich, a graduate student at the CUNY Graduate Center, and also a member of the BDNYC collaboration. Rothermich’s presentation demonstrated the power of citizen science projects, and how they can lead to important scientific progress with the invaluable contributions of the citizen scientist volunteers! The problem that Rothermich’s research was trying to address is that BDs often have huge degeneracies in their mass, temperature, and age, making it hard to tell these properties apart. Since it’s easier to determine these properties for regular stars (so-called “main sequence stars”), if one finds a regular star near a BD, one can assume they have similar fundamental properties since they must have formed together — then, by measuring the properties of the star, we can infer those of the hard-to-measure BD. This method is therefore called using “ultracool benchmarks”!
A collage showing some of the volunteers who participated in the Backyard Worlds project!
Via the citizen science project “Backyard Worlds,” Rothermich’s team was able to incorporate the work of over 175,000 volunteers who analyzed more than 1 million images from the WISE telescope — by flagging the images, the citizen scientists could indicate whether they found a candidate ultracool benchmark system. Their team then followed up 32 of these systems with spectroscopy, and those observations were often aided by citizen scientists.
Rothermich ended the presentation on a poignant and uplifting note, thanking the volunteers who participated for their time and effort, and talking about how his scientific career as an undergrad was also kick-started via the Backyard Worlds project, from the citizen volunteer side!
JWST Indicates Auroral Signature in an Extremely Cold Brown Dwarf
Comparison of two BD spectra showing a number of absorption features due to different molecules like water and CO2. A bump in one of the spectra (in blue) to the left indicates the presence of methane emission.
Next up was Jackie Faherty from AMNH, founder of the BDNYC collaboration, and co-founder of the Backyard Worlds project. Faherty’s results focused on Y-type BDs (the coldest kind), whose surface temperatures range from the setting on a home oven to that of a cold day at the North Pole! Her team used JWST spectra to study the atmospheric compositions of the BDs and found that they were chemically analogous to Jupiter with water ice, methane, carbon dioxide, etc. Faherty showed a comparison of two of their BD spectra, whose “spectra are sculpted by intriguing chemistry,” and discussed how one of them shows a characteristic bump from methane emission (see Figure 3, with the bump towards the left). Normally such a cold object shouldn’t be showing any emission spectra, but using the example of Jupiter they hypothesized that the emission could be due to aurorae at the poles of the BD (similar to those on Jupiter), and that these aurorae could be excited by the presence of a nearby active moon (like Io for Jupiter) or some other internal process. Faherty’s team plans on applying for more JWST time to follow up this system and learn more about whether it has a companion or not. Finally, she ended by discussing how the terms “planet” and “brown dwarf” are often ambiguous, which is why she prefers the term “other worlds” to encompass them all.
WASP-69b’s Escaping Atmosphere Is Confined to a Tail at Least 7 Planet Radii
The final presentation was by Dakotah Tyler, a graduate student at UCLA studying the exoplanet WASP-69b and its curious “tail”-like feature. WASP-69b is one of the 5,000+ known exoplanets, and it belongs to a sub-type known as “hot Jupiters,” or Jupiter-mass planets that orbit really close to their host star and are therefore quite hot. Hot exoplanets can often lose atmospheric mass due to the heating and escape of gaseous material, and Tyler’s team used WASP-69b as a test bed to study exoplanet mass loss in real time. They obtained transit data of the planet crossing the stellar disk, and by looking at helium absorption features in the atmosphere, they found that some of the helium was “blueshifted,” or appeared to be moving fast in our direction — indicating that it had been ejected from the planet’s atmosphere.
Animation showing what a comet-like exoplanet atmosphere “tail” would look like as it crosses in front of its host star.
The estimated mass loss rate they found is around one Earth mass per billion years, which is higher than previous studies had measured. They also found that although the planetary outflow might have initially been radial or spherical, by coming into contact with the host star’s stellar winds, it got reshaped into a comet-like tail. Finally, Tyler highlighted that their estimate of the size of the tail is roughly 7.5 Earth radii, which is again larger than previously measured for WASP-69b, thanks to the power of JWST!
High Energy Astrophysics Division Bruno Rossi Prize Lecture: Anatoly Spitkovsky (Princeton University) (by Ivey Davis)
In the Bruno Rossi Prize Lecture, Anatoly Spitkovsky of Princeton University succinctly summarized the underlying principle of the field of astrophysical plasmas: “How microscopic processes affect macroscopic astronomical objects.” Few systems (if any) better allow for us to examine the most extreme conditions where plasma physics operates than pulsars. As Spitkovsky recounts, since the discovery of pulsars by Dame Jocelyn Bell Burnell in 1967, the incredible consistency in the arrival time of pulsar pulses have been used for studying the structure of the interstellar medium, served as a test for general relativity, and were used as galactic-scale interferometers for studying gravitational waves as was covered in Monday’s first plenary. While pulsars also serve as a “playground” for theorists due to their extreme magnetic field strengths (billions to trillions of times that of the Sun’s field), densities (100 billion times that of Earth), and rotation rates (as short as a millisecond), there remain questions about the emission processes of pulsars that have persisted since their discovery.
Spitkovsky compares the problem-solving process of pulsar magnetic fields and emission to The Incredible Machine — you keep putting pieces together until something finally clicks and the solution is found, even if a bit convoluted (see associated figure). In the world of pulsar theory, more and more puzzle pieces have been incorporated as the computational power available has increased. For instance, until nearly the year 2000, models of pulsars assumed there was no surrounding plasma; this was relatively computationally inexpensive, but inherently non-representative of pulsar environments. To address this problem, the next piece introduced was a global plasma; this could reproduce how pulsars slow down over time, but could not explain the gamma-ray emission we observe. The most recent — and most computationally expensive — piece has been to transition from a global plasma to individual plasma particles that interact with both the magnetic field and each other. This has served to be the most reliable method to date to reproduce the gamma-ray double-peak light curve and the synchrotron spectrum as observed by the Fermi spacecraft, as well as some other unique pulsar emission.
Spitkovsky’s graphic to explain the process of solving problems for pulsar magnetospheres.
The conclusion of this work not only seemed to robustly address the age-old problem of pulsar magnetic field morphology and its interaction with plasma, but also fundamentally shifted how we understand where the emission is coming from. We now understand that gamma rays are likely generated by the merger of pockets of plasma, and that this occurs much farther from the surface than we originally assumed the emission to be originating from. This solution was decades in the making, and now that we have it, Spitkovsky is enthusiastic about the new opportunities it affords in addressing other phenomena that are unique to pulsars but inform our overall understanding of plasma astrophysics.
Press Conference: High-Energy Phenomena and Their Origins (by Yoni Brande)
Revealing Dual Quasars and Their Host Galaxy With JWST and ALMA: Yuzo Ishikawa (Johns Hopkins University)
Quasars, ultra-bright actively accreting supermassive black holes (SMBHs), are some of the brightest objects in the sky, often totally outshining the rest of the light from their host galaxies. Most galaxies have a single SMBH in their centers, but some galaxies have two! Yuzu Ishikawa and his collaborators presented their studies of “dual quasars.”
As the name implies, dual quasars have two accreting SMBHs, either as part of two merging galaxies or both in a single galaxy. Most of these have been observed at low redshift, but the dual quasar population at redshifts greater than 1 is not well understood. Perhaps there’s a connection between galaxy mergers and quasar triggering, or the properties of their host galaxies.
To answer these questions, Ishikawa and collaborators studied one particular dual quasar, DQ J0749, at a redshift of 2.17 (or over 10 billion years ago!). The quasars are separated by 3.5 kpc, and the system was discovered with the Hubble Space Telescope. Ishikawa was awarded JWST time to observe the system and found that extended H-alpha emission implies there’s a single host galaxy (a rotating disk!) and that the host is forming lots and lots of stars! The quasars in the system are pretty similar, possibly both accreting gas from the same region in the host. These observations are some of the best-quality data available on these enigmatic high-redshift systems, and Ishikawa and his collaborators hope to learn more about these with future observations.
There’s a well-known relationship between the mass of a SMBH and the mass of the stars in its host galaxy, with the stars outweighing the SMBH by a ratio of about 1000 to 1. However, there’s a population of “overmassive” SMBHS, which JWST has been finding at high redshift (z > 4). Fabio Pacucci and his collaborators studied these to find out if this is an observational bias, or if these mass ratios are being accurately estimated.
At these high redshifts, JWST is able (to paraphrase Dante) “to see the stars again,” allowing Pacucci and collaborators to estimate the stellar mass ratios in these galaxies. They found that, compared to local galaxies, there is a statistically significant difference in these mass ratios, going from 1000 to 1 nearby down to 100 or even 10 to 1 at high redshift.
These results are suggestive of the history of these black holes: by comparing black holes that started their lives light and those that are seeded heavy, the JWST results imply that these overmassive black holes must have started with heavy seeds.
Astronomical transients are non-periodic events that occur and disappear on short timescales. Fast radio bursts (FRBs) are a relatively new class of transients with enigmatic causes that manifest as highly energetic radio pulses on the scale of milliseconds. Alexa Gordon and her collaborators presented a study of FRB 20220610A, the farthest (z = 1) and brightest (4x brighter than any other) FRB yet observed.
Only about 50 or so FRBs have been localized to specific source galaxies, which is critical to understanding the processes that may produce them. Ground-based followup of FRB 20220610A showed inconclusive results as to its source, only showing either a large amorphous galaxy or a merging cluster of three smaller galaxies. Gordon’s team used the Hubble Space Telescope to re-observe the FRB source, and found that it actually originated from a compact group of seven galaxies that together are about the size of the Milky Way! Less than 1% of galaxies at this redshift occur in groups like this!
These galaxies appear to be tidally interacting, which can trigger star formation. Gordon speculates that this tells us about the source of the FRB, as one potential mechanism for FRBs are magnetars, highly magnetized young neutron stars which have very strong emission and are produced as a result of core-collapse supernovae. Gordon and her collaborators are hoping to continue to observe more of these types of FRBs, especially as upgrades to new observatories come online and continue to discover these sources at even higher redshifts.
Gamma ray bursts (GRBs) are the most powerful explosions in the universe. A typical GRB outshines every other source in the gamma-ray sky, combined! The Swift Observatory, NASA’s premier gamma-ray observatory, has detected more than 1,600 of these events across the sky.
GRBs come in many shapes and sizes, with differing energies and pulse traces, with short GRBs (< 2 seconds) typically thought to be produced by mergers of compact objects (like neutron stars or black holes) while long GRBs (> 2 seconds) are thought to be produced by supernovae. However, these are not hard classifications, and Lien and her colleagues turned to citizen science to more accurately classify these energetic signals to more accurately characterize them by their physical origins.
A test program showed that volunteer human classifiers (made up of a beta test group of astronomers and the interested public) perform better than existing GRB classification codes for sorting these traces by their observed shapes. Now, Lien and her collaborators are taking their program to the public, using the Zooniverse website to host their GRB classification data. You can join this project at https://www.zooniverse.org/projects/amylien/burst-chaser.
Seeing Our Sun Through a New Lens: The First Large Catalog of Hot Thermal Solar Flares: Aravind Valluvan (University of California, San Diego)
Solar flares, random broadband energetic bursts from the Sun, are a critical component of space weather. These events typically last about 20 minutes or so, but they could be as short as a few minutes or as long as half a day. These are the most energetic explosions in the solar system, and they have long been known to pose a threat to electronic communications infrastructure and sensitive operations like high-altitude aviation. These effects are important to study, in order to be able to predict them in advance and mitigate their effects.
Aravind Valluvan, from UCSD, studies these flares, looking specifically at “hot thermal flares”: flares with relatively symmetric light curves. The typical “impulsive” flare has a very quick, energetic rising phase and a much more gradual decay, while hot thermal flares increase and decrease in intensity on roughly the same timescales.
Valluvan says that while typical impulsive flares are caused by rapid magnetic field reconnection quickly dumping energy into the solar corona, hot thermal flares instead may be a result of slower magnetic reconnection processes, or slower energy transfer to the corona. Valluvan’s group observed 2,200 of these hot thermal flares and their catalog will be critical to properly interpreting these flares’ formation mechanisms. Are there connections between hot thermal flares and other solar phenomena like coronal mass ejections or solar particle events? Maybe! ISRO’s recently launched Aditya-L1 mission recently reached its final orbit, where it will use its X-ray spectrometer and ultraviolet imager to study the Sun and its energetic outbursts, just in time for solar maximum. Valluvan is hopeful that this mission will help us finally answer some of these critical questions.
Annie Jump Cannon Prize Lecture: Theories of Planet Formation, Eve Lee (McGill University) (by Briley Lewis)
For the 2022 Annie Jump Cannon Prize lecture, Eve Lee discussed the detailed (and quite complicated!) theoretical physics of planet formation. The planet populations we observe, she reminded the audience, are the consequences of coagulation and chemistry in the protoplanetary disk, disk–planet interactions, orbital dynamics, and atmospheric processes. She considered all these factors to try to explain: (1) a set of three puzzling (and seemingly contradictory) observations, (2) the origin of the Neptune desert, and (3) the favored location of Jupiter-like planets.
Let’s start with the trio of puzzling observations. First, outer giant planets appear to be more common around higher-mass stars. Second, inner super-Earths are more common around lower-mass stars. Third, systems with outer giants tend to have inner super-Earths. At first glance, it seems like the third observation is in tension with the first two — but Lee described in her talk (and also in a paper published last year) why these observations are actually reconcilable, and explainable by physics. Outer giants have inner super-Earths, because if a disk is large enough to form a giant planet, it also likely has enough mass to form a smaller super-Earth. Large stars have larger disks, so they form big planets, and small stars are able to convert pebbles to planetesimals more efficiently because they are cooler.
The Neptune desert — a notable lack of planets similar in size to Neptune in a region close to the host star — isn’t the result of just one factor, according to Lee. Part of the gap is from planets that just formed like that, lacking in metals to effectively cool themselves and accrete a gaseous envelope. Then, the gap is further carved by atmospheric evaporation caused by the star.
Finally, to determine why Jupiters so often form between 1 and 10 au, she considered what’s going on physically at each bound of that range. At the inner boundary, migration cuts off the ability for large planets to exist there. At the outer boundary, dust grains drift faster than they can grow, limiting the size of planets that can form.
Lee’s talk was a great reminder that planetary systems are extremely complex, and we have so much left to learn about how they become the worlds we observe — and even about how our own planet came to be.
Plenary Lecture: Sukanya Chakrabarti (University of Alabama, Huntsville) (by William Lamb)
Our galaxy rotates faster than it should if it only contains observable matter. This is why astrophysicists predict the existence of a dark matter halo surrounding the Milky Way to account for the extra, unobserved mass that must be there. The problem is, we don’t know much about dark matter because we have never observed it directly, and we don’t know how it is distributed in our galaxy. Sukanya Chakrabarti’s talk focused on probing dark matter by directly measuring the acceleration of stars within the Milky Way’s gravitational potential, which should bring further enlightenment on the effects of dark matter within a galaxy.
Traditionally, astrophysicists would estimate the acceleration induced on galactic stars by gravity by taking observations of the velocities and positions of those stars. This requires the assumption that galaxies are in equilibrium, where the gravitational potential and hydrostatic pressures that affect the motion of stars within the galaxy are balanced. However, galaxies are dynamic — interactions with satellite dwarf galaxies perturb galaxies over time. By directly measuring the acceleration of stars, Chakrabarti’s research enables the study of “real-time galaxy dynamics.”
Her group achieves this in four ways. First, they run dynamic simulations of the Milky Way, as opposed to simulations featuring static potentials. Second, they take high precision radial velocity observations, requiring a precision of 10 cm/s on velocity measurements, to measure the acceleration of some galactic objects. Third, they use pulsar timing measurements, such as those from NANOGrav, to effectively create a “galactic accelerometer” to measure the accelerations of pulsars. And fourth, they take measurements of the mid-points of exoplanetary eclipses, requiring a precision of 0.1 second across a 10-year baseline, to measure the accelerations of stars with exoplanets.
These measurements are extreme and on the edge of the technical capabilities of modern instruments and data analysis techniques. However, Chakrabarti is showing that this is possible, and hopefully insights from her work will further our understanding of dark matter in our galaxy.
