Snigdaa Sethuram Selected For The 2021 Flatiron Institute CCA Pre-Doctoral Program

Snigdaa S. Sethuram
Snigdaa S. Sethuram, CRA Grad Student

School of Physics and CRA Ph.D. student Snigdaa Sethuram has been selected by The Simons Foundation for the 2021 Flatiron Institute Center for Computational Astrophysics Pre-Doctoral Program.

The Center for Computational Astrophysics (CCA) at the Flatiron Institute is a vibrant research center in the heart of New York City with the mission of creating new computational frameworks that allow scientists to analyze big astronomical datasets and to understand complex, multi-scale physics in a cosmological context.

Snigdaa, who is part of Dr. John Wise’s Computational Cosmology group, will be working with 3 CCA mentors: Dr. Rachel CochraneDr. Chris Hayward, and Dr. Shy Genel to build the neural network that will emulate the computationally intensive radiative transfer calculations that are traditionally done by high-performance computers on a select set of simulated galaxies. These calculations fully leverage all the simulated information and output observable properties of the galaxies while also significantly reducing the overall cost — enabling more regular comparisons of simulations to observations in the observer space, where the simulation informs the observable properties and not the other way around.

The CCA Pre-Doctoral Program enables graduate student researchers from institutions around the world to participate in the CCA mission by collaborating with CCA scientists for a period of 5 months on site. With this opportunity, Snigdaa and others will be able to participate in the many events at the CCA and interact with CCA scientists working on a variety of topics in computational astrophysics, thereby deepening and broadening their skill sets.

Congratulations Snigdaa, for this outstanding achievement!

Bernard F. Schutz Elected as Fellow of the Royal Society

Bernard Schutz
Bernard F. Schutz

A School of Physics adjunct professor who served as a founding director of the Max Planck Institute for Gravitational Physics (Albert Einstein Institute – AEI), helped spark the creation of the Center for Relativistic Astrophysics (CRA) at Georgia Tech, and laid the analytical foundation in the search for gravitational waves is now the recipient of top honors from the world’s oldest independent scientific academy.

Bernard F. Schutz, also a professor in the School of Physics and Astronomy at Cardiff University, has been elected as a Fellow to the Royal Society, the United Kingdom’s national academy of sciences. Schutz joins a number of distinguished individuals in his scientific discipline — Isaac Newton, Albert Einstein, and Michael Faraday, to name a few — as a Royal Society Fellow. 

Schutz is honored and elected for seminal contributions to relativistic astrophysics, including driving the field for gravitational waves detection — ripples in time and space caused by violent and energetic celestial events, such as colliding black holes — research that helped lead to their direct detection in 2015. Georgia Tech played a direct and pivotal role in the analysis of the observed signal, and gravitational wave confirmations earned the 2017 Nobel Prize in Physics.

“My general reaction is one of pleasure and humility,” Schutz shares with the College of Sciences. “It is wonderful to be recognized for work that started 35 years ago and still continues, and it is humbling to be joining an academy that has such a distinguished membership.”

“It is a great honor to have professor Schutz as adjunct faculty to the CRA,” says Laura Cadonati, School of Physics professor, CRA director, and past deputy spokesperson for the Laser Interferometer Gravitational-Wave Observatory (LIGO). “His vision and advocacy have brought LIGO and gravitational waves to Georgia Tech, and made it possible for Georgia Tech to play a role in the discovery of gravitational waves and the exploration of the mysteries of the universe with this new messenger.”

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Kunyang Li to Lead a Talk for the 2021 HEAD Frontier Virtual Seminar Series

Kunyang Li
Kunyang (Lily) Li

The next HEAD (High Energy Astrophysics Division) Frontier Seminar will be held on Friday, April 16th at 1:00pm EDT (17:00 UTC). There will be three exciting talks by early-career researchers lined up, including CRA’s own Kunyang Li.

Ignacio Taboada Elected Spokesperson for IceCube South Pole Neutrino Observatory

School of Physics professor Ignacio Taboada officially begins his term as the next spokesperson for the IceCube Neutrino Observatory — an NSF-funded South Pole facility searching deep space for sources of high energy neutrinos — on May 1, 2021. Taboada recently joined outgoing spokesperson Darren Grant for a Q&A about IceCube’s progress and plans.

Ignacio Taboada, professor in the School of Physics and member of the Center for Relativistic Astrophysics at Georgia Tech, has been elected as spokesperson for the IceCube Neutrino Observatory, a collective of more than 300 scientists worldwide who work to detect neutrinos and other high energy streams of subatomic particles reaching Earth from deep space. The system of sensitive detectors — which takes up a cubic kilometer of South Pole ice — began in 1999 and has already yielded major discoveries about neutrinos, which are near massless subatomic particles that can travel unhindered for billions of light years from the most extreme environments in the universe to Earth.

Taboada joined AMANDA (The Antarctic Muon and Neutrino Detection Array), IceCube’s predecessor project, as a Ph.D. student in 1998, and has since added a number of major research responsibilities to his portfolio as IceCube has also grown. In 2017, Taboada and Ph.D. student Chun Fai Tung made significant contributions to the study of the first-ever detection of a neutrino in coincidence with a gamma ray flare from a ‘blazar’ — a type of galaxy with a super-massive black hole, in which a jet produced near the black hole points towards Earth. The blazar was the source of a high energy neutrino that set off IceCube detectors.

In recent years, researchers in the School of Physics at Georgia Tech have helmed a number of major collaborations and communications within the realm of astrophysics research and discovery — including the Nobel Prize-winning successful search for gravitational waves, through which a team of Tech’s astrophysicists joined thousands of scientists from around the globe in the LIGO (Laser Interferometer Gravitational Wave Observatory) detection effort. Laura Cadonati, professor in the School of Physics and the current director for Georgia Tech’s Center for Relativistic Astrophysics (CRA), has served as LIGO’s deputy spokesperson.

As Taboada, a fellow member of CRA, prepares to begin his tenure as IceCube’s spokesperson this May, he echoes that arc of leadership and the unique role that Georgia Tech and the School of Physics play within IceCube, LIGO, and other projects — and what that may mean for the future of other large-scale undertakings in this space:

“I think the relevance is that big science, as understood in terms of large scientific collaborations, is now clearly an important part of the scientific portfolio at Georgia Tech,” Taboada says. “If you look at the way that science has been changing within Georgia Tech, it’s clear that there are many changes for the better. The scientific output of Georgia Tech is improving, and improving over time. And I really hope that this is a sign of more things to come for physics and for science in general — and I really am very hopeful that Georgia Tech is going to play a big role within Gen2 (the next phase of IceCube’s development).”

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Gongjie Li, Billy Quarles, Nathaniel Moore win NASA grant to look deeper into star flybys and study possible planetary capture scenarios


Gongjie Li
Gongjie Li
Billy Quarles
Billy Quarles
Nathaniel Moore
Nathaniel Moore


 It’s not just Saturn that sports some celestial bling; many stars have rings or disks full of debris surrounding them, all leftovers from the process of planetary formation. That includes our Solar System, with its asteroid belt between Mars and Jupiter, as well as the Kuiper belt, the thicker, donut-shaped disk of icy rocks and comets that lies just beyond Neptune.

Somewhere within those stellar disks are important hints about how planets formed, as well as clues to the history of their host systems. That search now includes Gongjie Li, Billy Quarles, and Nathaniel Moore, three School of Physics researchers who recently won a $523,145 grant from NASA’s Astrophysics Theory Program (ATP) to study so-called “stellar flybys,” where stars fly over those discs, changing their form, scattering other celestial bodies hither and yon, and possibly giving birth to solar systems like our own.


An image of the cometary dust and exoplanet surrounding the young star HD 106906, which Georgia Tech physicists will study. (Image UC Berkeley)
An image of the cometary dust and exoplanet surrounding the young star HD 106906, which Georgia Tech physicists will study. (Image UC Berkeley)

A stellar flyby “is a common process, since most stars form in stellar clusters with a high number density of stars nearby,” says Li, an assistant professor in the School of Physics. “As the stars fly close to the debris disk, it will gravitational pull disk particles and excite their orbits.

 This changes the morphology of the disks, and the observed image of the debris disks could provide clues on the flybys and the formation environment of the planetary systems.”

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Sudarshan Ghonge Awarded the School of Physics 2021 Gil Amelio Award

CRA and School of Physics student Sudarshan Ghonge has been awarded the 2021 Gil Amelio Award for excellence in research by a graduate student.

SUDARSHAN GHONGESudarshan is a 5th year graduate student, working with Professor Laura Cadonati on gravitational wave astrophysics with LIGO. His research is focused on tests of general relativity and the connection between astrophysics and nuclear physics, by studying the signals from collisions of pairs of black holes and neutron stars.

Congratulations Sudarshan!
Time-frequency heat map of the gravitational wave signals from the first gravitational transient catalog (GWTC-1)

Time-frequency heat map of the gravitational wave signals from the first gravitational transient catalog (GWTC-1). Each panel in this poster represents one of the 11 gravitational wave events detected by the LIGO and Virgo detectors in their first and second observing runs from 2015 to 2017.

Sudarshan’s “Humans of LIGO” profile
College of Science 2017 feature

Georgia Tech Archives Rare Book Spotlight: Newton’s Principia & Opticks

On February 2nd, 2021 the Georgia Tech Library is hosting Dr. Jim Sowell and Research Services and Instruction Archivist Alison Reynolds for an exploration of and conversation about Sir Isaac Newton’s Principia and Opticks.

Get a virtual look at the Georgia Tech Archives copies of Newton’s Principia, which established the modern science of dynamics and serves as the basis for the modern study of physics, and Opticks, which provided our modern understanding of light and color. Participants will discuss intersections between rare books and science and why these works are pivotal to our current understanding of physics and astronomy.

The event begins at 12:00pm EST, to register for this event please visit


Bogdanović & Cadonati: Fierce Collaborators at the head of the CRA

The CRA leadership was featured in an article in the GT alumni magazine this month: Click here to read the full article.

In the Georgia Tech community, “creative friction” between collaborators leads to better solutions.

Georgia Tech physics professors Tamara Bogdanović and Laura Cadonati serve as the new leaders of the Institute’s Center for Relativistic Astrophysics. The pair both started in August (Cadonati as director, Bogdanović as associate director), and they work together closely to tackle wide-ranging goals to support initiatives linked to research, recruiting, and outreach.

Bogdanović’s primary training is in astronomy and Cadonati’s is in physics. Because of the duo’s distinct interests and expertise, they know they will come at problems from different perspectives and won’t make obvious errors as a result. “It’s always good to have a sanity check on your own thoughts and ideas,” says Bogdanović.

In fact, says Cadonati, the worst type of collaboration is when there is perfect alignment. “Diversity in training, opinion, and style is never a problem,” she says. “What complicates things is when people are too similar—they end up competing for the same resources and the same recognition.”

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CRA Highlights: A Look Back At 2020

What a year 2020 has been! 

It was a year of challenges and transitions that impacted each of our lives in important ways.

We managed a pandemic, work from our homes, virtual teaching and learning, too many BlueJeans meetings, a bit of anxiety, and physically distant goodbyes to old friends who moved to new homes. 

But we also welcomed new students, postdocs and staff, and we shared hope and successes.  We asked each faculty to share one 2020 highlight from their groups, and there is lots to be proud of in the CRA:


David Ballantyne published a paper in Nature Astronomy describing the interaction of a Type 1 X-ray Burst with a thin accretion disk. Graduate student Kunyang Li published two first author papers, in which she studied the pairing probability of massive black holes in merger galaxies, in collaboration with Ballantyne and Bogdanovic. Graduate student Julia Speicher published her first paper on Compton cooling of accretion disk coronae. Undergraduate student Xin Xiang co-authored a paper on models of warm coronae in AGN accretion disks.


Tamara Bodganovic’s group studied cold gas filaments forming around supermassive black holes in galaxy clusters and results from Yu Qiu’s simulation were published in and featured on the cover of Nature Astronomy. Her group also put constraints on the merger timescale of sub-parsec supermassive black hole binary candidates using Pulsar Timing Arrays.


Laura Cadonati’s group used gravitational wave data to populate the stellar graveyard with tens of merging black holes, contributing to GWTC-2 and several special-event LIGO papers. Graduate student Sudarshan Ghonge and undergraduate Richard Udall published first author papers.


Gongjie Li’s group is making strides in the studies of exoplanets, setting Theoretical constraints on exoplanets suspected of harboring moons.  Graduate students Nathan Moore and Hareesh Bhaskar published their first papers Inclination Excitation of Solar System Debris Disk Due to Stellar Flybys and Mildly-Hierarchical triple dynamics and applications to the outer solar system.


Nepomuk Otte’s group has studied very-high energy gamma ray pulsar wind tails with VERITAS and is in the final stretch of completing the Cherenkov telescope camera for a long-duration balloon flight around the South Pole in 2023 to search for ultrahigh-energy neutrinos.


Jim Sowell extended the reach of the GT Observatory Public Nights and celestial events to  online streaming.  The live Jupiter-Saturn conjunction was viewed by ~3000 people from around the world.


Ignacio Taboada’s group has studied a wide variety of potential high-energy neutrino sources, including X-ray binaries, choked GRBs, Seyfert galaxies and Blazars. PhD student Chun Fai Tung worked at South Pole (January 2020), performing necessary maintenance on the IceCube neutrino observatory.


John Wise and his collaborators received a NASA TCAN (Theoretical and Computational Astrophysics Networks) grant that supports work on the circumgalactic medium and its importance during galaxy formation.  Danielle Skinner was awarded the NASA FINESST Fellowship, fully funding her PhD research for the next three years, and Gen Chiaki will become an assistant professor at Tohoku University next year.


For the next year, we look forward to meeting in person our new members, to gathering around the whiteboard and seeing all of you at seminars in Boggs and Cosmic Coffees in Howey, to planning outreach events and socializing, to new initiatives, face-to-face interactions and more exciting science.

We wish you a fulfilling 2021, and stay safe!

Billy Quarles, Gongjie Li run their “theoretical constraints” on six exoplanets suspected of harboring moons

That’s No Exomoon: Astrophysicists Reveal Method For Finding Exoplanets’ Satellite Neighbors

An artist's rendition of Kepler 1625b-i and its exomoon candidate in the foreground
An artist’s rendition of Kepler 1625b-i and its exomoon candidate in the foreground (Image Wikimedia Commons)

It’s a famous “Star Wars: Episode IV” scene, so famous it has its own internet meme: Luke Skywalker mistakes the Death Star for a moon, but Obi-Wan Kenobi corrects him, accompanied by an ominous stab of John Williams’ music: That’s no moon.”

Billy Quarles, research scientist in the School of Physics and member of Georgia Tech’s Center for Relativistic Astrophysics (CRA), couldn’t resist the comparison when preparing a summary of new research on exomoons he conducted with fellow School of Physics colleague, assistant professor Gongjie Li, also a member of the CRA.

“Decades later, life imitates art where one frontier in astronomy is to detect a moon orbiting an exoplanet, or exomoon,” Quarles says in his summary of their work, to be published this month in Astrophysical Journal Letters and co-authored with Marialis Rosario-Franco, a Ph.D. candidate at the University of Texas at Arlington

Their letter establishes a framework for finding out whether exoplanets might have moons, and they had a chance to test that on the work of two Canadian astronomers who say there may be moons orbiting six exoplanets discovered with the Kepler Space Telescope.

Quarles’ and Li’s results? To paraphrase Obi-Wan, when it comes to four of the six exoplanets, those aren’t exomoons.

Exomoons Rising

Exoplanets are planets found outside our solar system. Telescopes couldn’t capture their image, so science had to wait for 1990s-era technology before confirming their existence. If moons of these planets do exist, they’re the ones now waiting for their moment in the scientific spotlight.

Exoplanets were first confirmed with improvements to measurements of radial velocity, which is the gravitational relationship between star and planet. “It seems that the detection of exomoons are waiting for a similar technological advance,” Quarles says.

The Kepler Space Telescope was launched in 2009 with the mission of finding exoplanets. Any stars found by it that may be harboring exoplanet candidates are first called Kepler Objects of Interest (KOI).

Earlier this year, University of Western Ontario astronomers Chris Fox and Paul Wiegert theorized that six exoplanets found via Kepler could be hosting exomoons. 

“They deduced the possible existence of exomoons by carefully measuring the difference in transit times for these exoplanets, where variations can indicate the presence of unseen bodies,” Quarles says. Transits are when a planetary body crosses in between a larger body and whomever is doing the observing.

“They found variations and alerted the astronomical community.  Since they could not confirm the exomoons directly, Fox and Wiegert admit that nearby planets could also be responsible for those variations, where the planet is tilted just enough relative to us so that it does not transit its host star,” he says.

All this is why exomoons “are on the frontier of detectability using current technologies, and theoretical constraints should be considered in their search,” Quarles says.

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