The David and Lucile Packard Foundation has awarded a Packard Fellowship for Science and Engineering to Ryan Foley, assistant professor of astronomy and astrophysics at UC Santa Cruz.
The Packard Fellowship, one of the nation's most prestigious honors for early-career scientists, gives Foley $875,000 over the next five years to support his research on the mysterious "dark energy" that is causing the expansion of the universe to speed up. Foley plans to use precise observations of exploding stars to better understand the properties of dark energy.
"Ryan is one of the top young astronomers in the world," said Professor Enrico Ramirez-Ruiz, chair of the Department of Astronomy and Astrophysics. "He has an exceptional research portfolio in the area of cosmology and high-energy astrophysics. We count ourselves lucky to have his vision, energy, and charisma in the department."
Dark energy was discovered through observations of a particular type of exploding star, called type 1a supernovae. The predictable brightness of these stellar explosions makes them useful for measuring cosmic distances. But more precise measurements are needed to probe the nature of dark energy and determine if it is constant or variable over time. Foley is leading two supernova survey projects designed to bring supernova cosmology to a new level.
"Dark energy accounts for roughly 70 percent of the universe, yet we know barely anything about it," Foley said. "These new surveys should improve our knowledge of the nature of dark energy far beyond previous efforts."
Nearby supernovae
Foley is working to get better observations of nearby supernovae. For years, astronomers have focused most of their efforts on the distant universe to record observations of the faintest, most distant supernovae. Because it takes billions of years for light from distant objects to reach our telescopes, observing distant supernovae provides a look back in time and allows astronomers to study the history of the universe's expansion. According to Foley, however, the biggest problems in supernova cosmology currently relate to nearby supernovae.
"It's funny how the problem is inverted now, and the hard thing is to get good observations of the nearby universe," he said. "Currently, the sample of nearby type 1a supernovae is a larger source of uncertainty in cosmology experiments than the distant sample."
One reason is that the number of nearby galaxies is limited, and surveying them for supernovae requires searching large areas of the sky. In contrast, deep observations of a relatively small patch of sky can explore a large volume of the distant universe (just as your hand at arm's length covers a much larger area of the sky than the moon, yet the moon is vastly larger than your hand).
With modern telescopes and survey projects, the rate of discovery of supernovae has grown exponentially in recent years. Foley and a small team launched the Foundation Supernova Survey in 2015 using the Pan-STARRS telescope in Hawaii, which has the largest digital camera in the world (1.4 billion pixels) and is extremely well calibrated. Because comparing brightness measurements is so crucial to supernova cosmology, precise calibration of the telescope system is essential. Pan-STARRS has already observed the entire sky visible from Hawaii, providing necessary reference images, and Foley was part of an earlier collaborative project that used Pan-STARRS to observe about 3,000 distant supernovae.
"Pan-STARRS is the only system with supernovae at all distances, so we can directly compare all supernovae on the exact same system, eliminating cross-system calibration uncertainties," Foley said.
His other project, the Swope Supernova Survey, will complement the Foundation Survey with more detailed observations of individual supernovae. Foley is working with astronomers from the Carnegie Observatories to use the Swope Telescope at Las Campanas, Chile, which will enable him to obtain detailed "light curves" showing how the brightness of a supernova rises and then fades away over time.
"The combination of these two surveys will allow us to make the best dark energy measurements to date," he said.
Foley is the 12th UCSC faculty member, and fifth UCSC astronomer, to receive a Packard Fellowship, awarded by the David and Lucile Packard Foundation to support young scientists and engineers who show exceptional promise and creativity. It is one of the nation's largest nongovernmental fellowships, designed to allow maximum flexibility in how the funding is used. Packard Fellows are encouraged to take risks and explore new frontiers in their fields.
Foley received his bachelor's degree in math, physics, and astrophysics from the University of Michigan and M.S. and Ph.D. degrees in astrophysics from UC Berkeley. In 2015, he received a Sloan Research Fellowship. He came to UC Santa Cruz from the University of Illinois in 2016.
