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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A new framework for cold filament formation in galaxy clusters

Volume 4 Issue 9, September 2020
Nature Astronomy: The ups and downs of cluster gas, Volume 4 Issue 9, September 2020 (Image: Yu Qiu, KIAA-PKU/Georgia Tech Cover Design: Bethany Vukomanovic)

In a Nature Astronomy Letter, Yu Qiu (KIAA Fellow/Georgia Tech), Tamara Bogdanović (Georgia Tech), Yuan Li (UC Berkeley), Michael McDonald (MIT), and Brian R. McNamara (U Waterloo) report on the formation mechanism of dusty, cold filaments in cool-core clusters based on radiation-hydrodynamic simulations of AGN feedback, shedding light on how supermassive black holes interact with the intracluster medium.

Read the Full Letter

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Danielle Skinner wins NASA grant targeting graduate students

Physics Student’s Search for Precious Metals from Neutron Stars Hits the Funding Motherlode

Neutron stars collide, and a swarm of heavy elements like gold and platinum shoot out into the universe. Danielle Skinner wants to learn more about that process, and thanks to NASA, she won’t have to worry about funding that research for the next three years.

Danielle Skinner, graduate student and NASA FINESST Award winner, School of Physics

Skinner, a graduate student of associate professor John Wise in the School of Physics, is the winner of a NASA FINESST (Future Investigators in NASA Earth and Space Science and Technology) Award. Only 19 of 158 astrophysics proposals were selected for the fellowship.

“I was surprised to see that I had been selected,” says Skinner, a graduate teaching assistant. “I had to read the email a few times over for it to really sink in.”

“I was ecstatic when I first received news of Danielle’s fellowship,” Wise says. “I am very proud of her. This independent fellowship is very prestigious, and gives Danielle the freedom to explore the mysteries of the early universe.”

Through the FINESST program, NASA’s Science Mission Directorate (SMD) “solicits proposals from accredited U.S. universities and other eligible organizations for graduate student-designed and performed research projects that contribute to SMD’s science, technology and exploration goals,” according to a space agency press release.

Dr. John Wise, Associate Professor of Physics Center for Relativistic Astrophysics
Dr. John Wise, Associate Professor of Physics Center for Relativistic Astrophysics

“FINESST awards research grants with a research mentor as the principal investigator and the listed graduate student listed as the student participant. Wise, who is also a member of Georgia Tech’s Center for Relativistic Astrophysics, is listed as principal investigator (PI) and Skinner is the future investigator (FI).

“Nucleosynthesis from Neutron Star Mergers in the Early Universe” is the title of Skinner’s proposal. It will take Wise and Skinner back to the early stages of the universe through simulations. An ongoing quest in astrophysics is understanding the evolution of the periodic table, and in particular, figuring out where some of the heaviest elements, like gold and platinum, actually came from.

“We think that in the early universe, merging neutron stars could provide the right environment for these elements to form, and eventually, those heavy elements would end up in stars that we see today,” she says.

Skinner will run a series of simulations where she models neutron star mergers with varying parameters to try to find those with heavy metal abundances.

Original Article

Online Public Nights: Georgia Tech Observatory Offers Live Looks, Virtual Tours of Venus and the Moon

*For those interested in learning more about astronomy, the next public night will be live-streamed on May 28 at 9:30 PM on the Georgia Tech Observatory YouTube, weather permitting. Mark the date to enjoy a guided tour to the marvels of our universe — from wherever you may find yourself in it!

On May 7, as a full moon came into focus in the night sky, several hundred computer screens lit up for a showing of the evening’s “supermoon” Flower Moon. Through a live stream on YouTube, curious observers tuned into the Georgia Tech Observatory’s first online public night, and were treated to live looks and a guided tour of Venus and Earth’s moon. 

Since the Observatory opened in 2007, public nights have traditionally been held on the roof of Howey Physics Building, where four telescopes reach deep into the night sky, and visitors of all ages gather to learn about the wonders of the universe together. But with this year’s campus closures and event cancellations due to COVID-19, spring and summer nights at the Observatory were shaping up to be rather quiet ones — until Observatory Director Jim Sowell teamed up with a colleague to quickly take the outreach program online. 

James Sowell, director of the Observatory, during a previous public night. Photo: Rob Felt
James Sowell, director of the Observatory, during a previous public night. Photo: Rob Felt

The two-man crew of Sowell and telescope operator John Wallom directed Tech’s inaugural online public night at the Observatory, focusing a telescope connected to a live stream for an in-depth tour of Venus and the moon. Moving from craters to mountains to “lunar maria” — large, dark, basaltic plains on Earth’s moon, formed by ancient volcanic eruptions — Wallom controlled the telescope and handled telecommunications, while Sowell explained the topographies and histories of two of the brightest celestial objects that light up our night sky.

“I have always enjoyed showing views of celestial objects to others,” says Sowell. “It is my opportunity to give a person a peek through a window into the universe.” 

During a typical Observatory night, hundreds of curious students and visitors flock to Howey to see the wonders of space. And when Sowell shows visitors planets in person, he says their live reactions confirm his belief in the magic of studying the stars. 

“The best aspect about my job is the excitement people share when they see the cratered surface of the moon,” says Sowell. “Many often squeal! It is the celebrated joy of personal discovery and experience which is why astronomers host such events.” 

While the adjustment to an online public night prevented Sowell from seeing those reactions in person, he shared that public feedback from far-flung viewers in Florida, Tennessee, and Brazil affirmed the night as a success. 

Sowell notes that observatories across the nation carry the responsibility of making astronomy accessible to the public. He says that hosting public nights, that bring the wonders of astronomy to the Georgia Tech community and beyond, has always been a focus for the Observatory. Public nights can also foster curiosity and interest in exploring our universe at an early age. 

“I have been in love with astronomy and the night sky since I was very young,” says Sowell. “I got my first telescope when I was seven years old.”

The work of the Georgia Tech Observatory has grown and evolved over time. Several courses, research endeavors, development of the Georgia Tech Astronomy Club, and outreach to the greater Atlanta area are centered as critical facets of the Observatory’s efforts. One example of this work includes a current collaboration between several researchers from the Daniel Guggenheim School of Aerospace Engineering and several GTRI scientists and engineers, who have teamed up to use the Observatory’s telescopes to measure characteristics of earth-orbiting spacecraft. 

Sowell shares that one long-term goal is incorporating astronomy into the educational framework for younger students, with the intention of fostering an early interest in astronomy and general scientific discovery.  

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Richard Udall Selected For The Joyce M. and Glenn A. Burdick Award

Center for Relativistic Astrophysics undergraduate student Richard Udall has been selected for the Joyce M. and Glenn A. Burdick Award from the College of Sciences! Recipients of this award are rising seniors in Physics, demonstrate scholastic achievement, leadership in the School of Physics, and possess characteristics that embody the mission of Georgia Tech.

Congratulations, Richard!