Two graduate students who recently completed their doctoral degrees in the Department of Astronomy and Astrophysics have been recognized for their outstanding scientific achievements by the International Astronomical Union. Guang Yang was selected to receive the 2019 IAU PhD Prize in the High Energy Phenomena and Fundamental Physics division, and Gudmundur Stefansson was named the runner-up in the Technologies and Data Science division. Yang will be presented with a certificate at the 2021 IAU General Assembly meeting in Busan, South Korea.
Yang’s research, completed under the supervision of W. Niel Brandt, Verne M. Willaman Professor of Astronomy and Astrophysics and professor of physics, focused on using cosmic surveys to understand what drives the growth of central black holes in galaxies over most of cosmic time.
“As part of my research, I used data from massive X-ray surveys like Chandra Deep Field-South & North and COSMOS-Legacy to study the evolution of black holes and their host galaxies starting 12 billion years ago,” said Yang.
Black holes are commonly found at the centers of massive galaxies. It was thought that black-hole growth was related to the overall rate of star formation in its host galaxy, but Yang found that it is more closely related to the stellar mass of some galaxies. His research also directly shows that black holes coevolve with the host galaxy’s galactic bulge—the tightly packed group of stars usually near the center of the galaxy—rather than entire galaxy.
“Guang’s Ph.D. thesis accomplishments were superb, and he delivered some of the best results in the world on how distant massive black-hole growth depends upon galaxy properties and cosmic large-scale structures,” said Brandt. “This was possible due to a combination of scientific creativity, strong skills in data analysis and interpretation, and an incredible work ethic and drive for excellence. Guang led or co-authored an astonishing 15 cutting-edge papers during his Ph.D. studies.”
Yang is currently a postdoctoral research associate at Texas A&M University, working to prepare for exciting new science with the soon-to-launch James Webb Space Telescope.
Stefansson’s research, completed under the supervision of Suvrath Mahadevan, professor of astronomy and astrophysics, focused on improving scientists' ability to detect and characterize exoplanets—planets outside of our solar system—using ground-based telescopes. He was involved in the development, construction, and deployment of two next-generation spectrographs: the Habitable Zone Planet Finder on the 10m Hobby-Eberly Telescope at McDonald Observatory in Texas and the NEID on the 3.5m WIYN telescope at Kitt Peak National Observatory (KPNO) in Southern Arizona. These spectrographs detect exoplanets by measuring the slight periodic shift in a star’s radial velocity due to the subtle gravitational “tug” of the planet on its star.
“These next-generation planet-hunting spectrographs are opening the doors to better detect and characterize planets in the habitable-zones—the region around a star where liquid water could exist on a surface of a planet—around our nearest stellar neighbors,” said Stefansson. “I can’t wait to see what we will find!”
Additionally, Stefansson developed inexpensive “engineered diffusers”—carefully structured micro-optical devices—that can be easily installed onto a variety of telescopes to minimize distortions from the Earth’s atmosphere and from the instruments themselves during ground-based photometry. These engineered diffusers have been installed and are in active use at a number of telescopes across the world, including the 3.5m telescope at Apache Point Observatory, and have produced some of the highest precision photometry measurements from the ground.
“Gudmundur's thesis research was truly impressive in developing new techniques for precision photometry and spectroscopy, and also combining these techniques to increase our understanding of planets and the architecture of planetary systems,” said Mahadevan. “The diffuser-assisted photometry technique he demonstrated in his thesis rivals the precision of space-based photometry from the ground, and yet is accessible to amateur astronomers as well.”
Stefansson is currently a Henry Norris Russell Postdoctoral Fellow at Princeton University, where he is using these technologies to detect and precisely characterize nearby exoplanets.