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.

You can read Astrobites’s interview with Kerstin Perez here.

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.

Table of Contents:

• 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)
• Press Conference: More Stars and Distant Worlds
• Plenary Lecture: When Data is Not Enough: Illustrating Astrophysics for the Public (Robert Hurt, Caltech/IPAC)
• Press Conference: Citizen Science from the 2023/2024 Solar Eclipses
• Royal Astronomical Society Gold Plenary Lecture: Challenges to the Cosmological Model (John Peacock, University of Edinburgh)
• 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)

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]

An image of one of Rodriguez’s slides, showing the output of the Great Balls of FIRE simulation. [Slide by Carl Rodriguez]

You can read Astrobites’s interview with Carl Rodriguez here.

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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.

You can view a video recording of this press conference or take a look at the presenters’ slides.

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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]

You can read Astrobites’s interview with Robert Hurt here.

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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]

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]

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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.

You can read Astrobites’s interview with John Peacock here.

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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!

A summary of the current (as of 2022) fleet of heliophysics missions. [NASA’s Goddard Space Flight Center]

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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.

Table of Contents:

• 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)
• Press Conference: From the Galactic Center to the Galactic Disk
• Unlocking the Mysteries of Exoplanets: The Crucial Role of Laboratory Research (Erika Kohler, NASA Goddard Space Flight Center)
• Press Conference: Massive Black Holes and Surprising Spirals
• Plenary Lecture: Leveraging AI to Transform the Astronomy Data Revolution into a Discovery Revolution (Cecilia Garraffo, Center for Astrophysics | Harvard & Smithsonian)
• Plenary Lecture: With a Wild Surmise: A New Era of Exoplanet Exploration (Tom Beatty, University of Wisconsin at Madison)

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]

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.

You can read Astrobites’s interview with Venkatesan and Pugh here.

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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]

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]

You can view a video recording of this press conference or take a look at the presenters’ slides.

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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]

A slide from Kohler’s talk showing a sprawling graph-map diagram of the many features studied in exoplanet research. [Slide by Erika Kohler]

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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]

Illustration of a quasar with outflowing winds. The spectra at the top right shows how the absorption line has shifted to bluer wavelengths over time. [NASA/CXC/M. Weiss, Catherine Grier and the SDSS collaboration]

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]

You can view a video recording of this press conference or take a look at the presenters’ slides.

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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]

You can read Astrobites’s interview with Cecilia Garraffo here.

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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]

You can read Astrobites’s interview with Tom Beatty here.

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