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Both projects made headlines around the world, particularly in stargazing circles. Pretty good work for someone from an astronomy program of only three faculty. (“We’re small but mighty,” Hall said.)

However, if researchers like Hall and her colleagues keep doing things that reshape our understanding of the formation of our universe, the reputation of UGA’s astronomy program soon will far outstrip its modest size.

Occam’s telescope

Hall is a computational astrophysicist. She applies for time at telescopes like the Atacama Large Millimeter/submillimeter Array (ALMA) in the Atacama Desert of northern Chile—time that is awarded very competitively to astronomers worldwide—then runs the collected data through supercomputers to analyze and conduct simulations of cosmic events. Until the Nature paper, that’s all GI researchers had to go on: simulations.

“When I first started working on gravitational instability in 2013, it was kind of considered—I don’t want to say a fringe theory, because that’s not true,” said Hall, assistant professor of computational astrophysics in the Franklin College of Arts and Sciences . “It was like it was acknowledged that it was important, but it had never been definitively observed.”

When she arrived at UGA in 2020, Hall was already making plans to change this. That year she was lead author on that predicted how GI would influence movement in planet-forming disks, based on the research team’s simulations. Four years later, one reason the Nature paper made such a splash was that the data collected from ALMA matched their predictions.

“We had tantalizing hints that AB Aurigae was gravitationally unstable—it was massive, it had those spiral arms and some protoplanet candidates that seemed to be quite large, and it made us think this was probably the best chance we’d have for catching GI in action,” Hall said. “What we really needed was the kinematic evidence of how the disk was moving.”

ALMA provided just what they needed. There were the images themselves, gathered through ALMA’s array of 66 radio telescopes. Taking pictures of a star system 509 light years away, Hall and her colleagues could see features roughly the size of the distance between Earth and the sun. “That doesn’t sound like a lot,” Hall said, “but it’s like looking at your ceiling and seeing something 7,000 times smaller than the width of a human hair.”

Among the differences between GI planet formation and formation via core accretion is how the gas and debris in the circumstellar disk move. Core accretion works exactly how it sounds: Cosmically tiny particles accumulate toward the disk’s center and develop into kilometers-sized planetesimals, which themselves begin merging into larger objects. It is essentially a bottom-up or center-out process.

GI works more outside-in. Cooling temperatures in the spiral arms produce localized variations in gravity, which collapse first into themselves and then into each other. Conventional thinking has held that GI formation occurs only in very young disks and produces only gas giants akin to Jupiter, but a growing body of observational evidence contradicts this thinking. This inconsistency has led astronomers to posit all sorts of tweaks or special circumstances to both the GI and core accretion models to try to explain what they were seeing.

Hall and her colleagues helped answer some of the riddles. First, ALMA works at longer wavelengths than visible light, enabling it to see through clouds of cosmic gas that can obscure other types of telescopes. It also can detect movement through what are called molecular line observations, measuring the wavelengths of light emitted from molecules like carbon monoxide. These light emissions display a Doppler shift, meaning the wavelength is longer when the molecule is moving away from us, and vice versa. By taking multiple snapshots and measuring the light, the team could recreate how the disk was moving and compare to their predictions.

One of the key findings was the detection of a “GI wiggle” that the researchers had predicted through their simulations. This wiggle is produced by the localized gravity variations in the spiral arms, causing gas and dust in those areas to move at different speeds; planets forming in disks via core accretion typically produce only one local variation (at the center where the protoplanet is forming), but the AB Aurigae disk yielded up several.

Second, Hall’s colleague Cristiano Longarini from the University of Cambridge illustrated how GI could form smaller planets by calculating the theory in its entirety. In previous studies, the presence of cosmic dust had been discounted “for simplicity’s sake,” Hall said. Once Longarini did the math to account for dust, the team saw that “it should be possible for GI to form planets all the way down to roughly Earth-mass objects.”

“What I like about gravitational instability,” Hall said, “is it’s like an Occam’s razor thing. You don’t have to keep adding all these additional knobs and factors, and turn the dial and do this and that. It just exists. It comes naturally from the numerical simulations we do—if the disk cools fast enough, parts of it collapse. It can naturally explain some of the phenomena we’re seeing.”

Interstellar Cosmographic Explorer

In February 2020—“Just before the world closed down,” as she tells it—Hall visited UGA as a prospective faculty member. She was a postdoctoral fellow at the University of Leicester in England who had already done work impressive enough that it would later that year.

After interviewing at multiple universities, Hall chose the school in the small Southern town with a very appealing vibe.

“I just absolutely fell in love with the place,” Hall said of Athens and UGA. “I knew I’d be happy here. I wanted somewhere where I had students who would work hard with me, a place where I felt like I could make a difference in the department. Who wouldn’t choose that?”

Hall is one of nine tenure-track faculty in Franklin College’s , but she’s one of just three current UGA astrophysics professors out of 23 total in the Department of Physics and Astronomy (three other astrophysicists retired in 2025). With a third of the department’s 60 or so graduate students focusing on astrophysics, along with half of its 120 undergraduates majoring in astronomy, this reflects an imbalance. On top of this, the department’s observatory and telescope have been under repair since prior to Hall’s arrival.

But a new day may be dawning for UGA astronomy. Department head and Professor Phillip Stancil is looking to hire multiple faculty, including a cluster hire in planetary sciences. Historically UGA has focused on astrophysics and simulational astronomy, but Stancil said he is launching a planetary sciences initiative that will include other departments such as chemistry and geology (which Klimczak calls home). And Hall is working with the Franklin College development office to identify a donor to help get UGA’s observatory looking skyward again.

Still, one thing is clear as a starry night: Since arriving at UGA, Hall has thrived. A couple years after the Winton Award came the photosynthetic zone and GI papers and their subsequent media attention. In 2024 she delivered a well-received TEDx Talk about her hunt for coalescing exoplanets. Then, early last year, Hall , one of only 20 selected from 3,000 applicants. The honor will bring her additional research funding, as well as opportunities for professional development and training.

“When we hired Cass,” Stancil said, “we were looking for someone who was a star. And we got a star.”

Currently Hall is “working on predictions for future missions” and playing her cards close to the chest. But one thing she’s happy to share is how she feels about her move South.

“After my wife and I moved here—obviously, with the pandemic, everything was a bit crazy moving over—but when we settled, I asked her, ‘What do you think?’” Hall said. “And she was like, ‘Yeah, you were right. This is where we were meant to be.”