Astrophysics and Cosmology// Daniel Perrefort
The Astrophysics and Cosmology group focuses mainly on cosmology (the properties and evolution of the universe and growth of large scale structure), galaxy evolution (how galaxies grow and change over time), and supernovae (causes of Type-Ia supernovae, modeling the spectrum of emitted light, use as standard candles to measure the expansion of the Universe). We approach these problems using theoretical, computational, and observational techniques. We are involved with a number of current and upcoming astronomical survey projects which can address these questions.
Supernovae are the largest explosions known in the Universe, occurring when a star or stellar remnant is no longer able to support itself against the pull of gravity. As it collapses, the sudden release of gravitational potential energy drives an explosion. John Hillier has built the world's leading non-equilibrium radiative transfer code to model the radiation we observe escaping from supernovae; he also uses this code to model the most massive known stars. Carlos Badenes studies supernova remnants to figure out what causes Type-Ia supernovae; his work has given support to the hypothesis that merging binary white dwarfs are responsible for most of these explosions. Michael Wood-Vasey has used Type-Ia supernovae as standard candles to measure the expansion history of the Universe; his work has helped make the case that the Universe's expansion is accelerating. Daniel Perrefort is improving our ability to measure the expansion history of the Universe by identifying peculiar Type-Ia supernovae that have inaccurate distance measurements.
The cause of this accelerating expansion is one of the central questions of cosmology, along with the nature of dark matter, the physics of the very early Universe, and the growth of large scale structure. Andrew Zentner is a theorist who has worked on dark matter probes via gravitational lensing and evolution of stars. Arthur Kosowsky has addressed many of these questions using the theory of the cosmic microwave background radiation. Zentner and Kosowsky pursue constraints on particle physics using cosmological data, while Kosowsky and Dan Boyanovsky both study early-universe inflation.
The formation and evolution of galaxies, including their interactions with their environments, remains a major area of interest in astrophysics. Many cosmological probes rely on galaxies, especially their distances from us. Jeff Newman and Brett Andrews are observational astronomers who specialize in methods for measuring distances to galaxies from images and understanding how galaxy properties change with time. Rachel Bezanson is an observational astronomer whose research focuses on empirical studies of the formation, transformation, and evolution of massive galaxies through cosmic time. Dave Turnshek and Sandhya Rao study quasar absorption line systems. Evan Schneider is a computational astrophysicist who studies how gas and stars in galaxies interact by running numerical simulations on supercomputers.
A common theme connecting much of the work in the group is the use of astronomical survey techniques. The University of Pittsburgh was a member of the groundbreaking Sloan Digital Sky Survey. Michael Wood-Vasey served as Scientific Spokesperson for SDSS-III; Brett Andrews, Jeff Newman, Michael Wood-Vasey, and Carles Badenes are involved with SDSS-IV; and Carles Badenes continues as a member of SDSS-V. Most of our faculty have used SDSS data in their work. Jeff Newman and Carles Badenes are both involved with the Dark Energy Spectroscopic Instrument (DESI), a project to build the next-generation wide-field multi-object spectrograph. Jeff Newman is a key member of the CANDELS survey, the largest-ever sky survey using the Hubble Space Telescope. Arthur Kosowsky participates in the Atacama Cosmology Telescope (ACT) collaboration, which makes arcminute-resolution maps of the microwave sky. Rachel Bezanson has been involved with a number of large galaxy surveys spanning from the local Universe to a few billion years after the Big Bang including the NMBS, 3D-HST, and OBEY surveys. She is a survey scientist for the LEGA-C (Large Early Galaxy Astrophysics Census) ESO Public Spectroscopic Survey and is actively involved in planning for the Galaxy Evolution component of the Prime Focus Spectrograph Survey. Finally, several of the faculty have leadership roles in the Rubin Observatory Legacy Survey of Space and Time (LSST) project (Zentner, Wood-Vasey, Newman). Related to survey astronomy, Newman, Andrews, Wood-Vasey, and Badenes are all interested in astronomical data-mining techniques and related statistical questions.
The Astrophysics and Cosmology group generally supports around twenty graduate students and one or two postdoctoral researchers. We also encourage undergraduate involvement in research. The STEPUP program (Survey of Transiting Exoplanets at the University of Pittsburgh) uses a telescope at Allegheny Observatory to discover planets orbiting candidate stars identified by the Kepler satellite, and is run entirely by undergraduates.
Group members participate in activities of PITT PACC and organize workshops on astrophysical topics. We hold regular Astro Coffee meetings to discuss new discoveries and research results; these meetings are open to anyone who is interested. Members of the group also organize educational activities at Allegheny Observatory, including public lectures and observatory tours.