Astrophysics and Cosmology

Emphasis Areas

  • Observational, numerical, and theoretical cosmology
  • Dark matter and dark energy
  • Galaxies
  • Active galactic nuclei and quasars
  • Interstellar and Intergalactic medium
  • Stellar atmospheres and massive stars
  • Supernovae and Supernova Remnants
  • Physics of the early universe

Astrophysics and cosmology research at the University of Pittsburgh is pursued by a diverse group of observers and theorists engaged in studies that range from the properties, evolution, and death throes of massive stars; to the formation of galaxies; to the production of dark matter in the early universe. Members of the group are Carles Badenes, Daniel Boyanovsky (also condensed matter physics and particle physics), Desmond “John” Hillier, Arthur Kosowsky, Ezra “Ted” Newman (emeritus), Jeffrey Newman, Sandhya Rao, Regina Schulte-Ladbeck, David Turnshek, Jon Weisheit (also condensed matter physics), Jeffrey Winicour, Michael Wood-Vasey, and Andrew Zentner.

Theorists in the group often work closely with observers and experimentalists on questions that are driven by both existing and future observational facilities. This breadth fosters active collaborations with particle physicists, statisticians, computer scientists, and other researchers at institutions in the United States and abroad. Researchers study massive stars, interacting binary systems, and their supernova descendents to address fundamental questions about the evolution of stars and their environments. Supernova progenitors (both massive stars and interacting binary systems) play an important role in galaxy evolution because they not only enrich galaxies with nuclear-processed material but also can disrupt as well as initiate star formation as supernovae shockwaves propagate through the interstellar medium and molecular clouds in galaxies. The process of galaxy formation, which includes the conversion of gas into galaxies of stars, is rich and complex. The properties and evolution of galaxies are presently being studied as part of the Sloan Digital Sky Survey (SDSS), Deep Extragalactic Evolutionary Probe 2 (DEEP2), and DEEP3 Galaxy Redshift Surveys. To further clarify the process of galaxy formation, collaborative work being done within the All-Wavelength Extended Groth Strip International Survey (AEGIS) is an endeavor to map a specific patch of sky across a wide range of wavelengths, from x-rays to radio. In the future, these types of investigations will continue with the Panoramic Survey Telescope and Rapid Response System (Pan-STARRS) and the Large Synoptic Survey Telescope (LSST) collaborations. These large surveys provide the high statistical accuracy required to address many fundamental problems in galaxy formation and evolution.

Members of the group also use space telescopes, such as the Hubble Space Telescope (HST), and large ground-based telescopes throughout the world to probe phenomena of current interest. Specific investigations include studies of outflows from the most massive stars, environmental influences on the formation and evolution of galaxies, the evolution of Supernova Remnants and their interaction with the surrounding interstellar medium, the properties of gas in galaxies through observation of the imprint that the gas leaves on the spectra of background quasars, and quasars themselves (extremely energetic phenomena associated with accretion of matter onto super-massive black holes in the centers of galaxies). Because of the complexity of the many astrophysical processes, theorists working in support of the observational efforts use a variety of techniques to address open questions in galaxy evolution, such as: How did the first galaxies form? What role do super-massive black holes play in this process? How can observations be used to determine the physical properties of quasars? What are the properties of the smallest galaxies found orbiting our own Milky Way Galaxy? To explore these questions, University of Pittsburgh astrophysicists often use sophisticated radiative transfer codes or numerical simulations of nonlinear phenomena. For example, this might include following the transfer of radiation through the wind of a massive star or an accretion disk; violent collisions among grand spiral galaxies; or the deaths of stars, which result in powerful supernovae that spread heavy elements (elements heavier than hydrogen and helium) throughout their host galaxies.

One of the foundations of physics and cosmology is gravity theory (the General Theory of Relativity). Studies continue in both classical and numerical relativity, including following the behavior of light in curved space times, modeling gravitational lenses, and predicting the frequency and amplitude of gravity waves from realistic astrophysical scenarios. In the past decade, modern cosmology has had some exciting new developments. Cosmology, the study of the structure and evolution of the universe, is entering its “dark days.” Studies in cosmology can be used as a laboratory to investigate fundamental physical laws. All galaxies appear to require some additional, unseen mass to bind them together. This is called dark matter. Observations of the cosmic microwave background (CMB) and the clustering patterns of galaxies in surveys like SDSS and DEEP2 indicate that a quarter of the energy in the universe resides in dark matter. Despite this, dark matter has yet to be identified in any terrestrial laboratory. Equally intriguing, recent measurements indicate that 70 percent of the energy in the universe takes the form of “dark energy,” which drives an accelerated cosmic expansion. Current ideas as to the nature of dark energy are few and speculative, so the name is a catch-all for whatever causes the observed acceleration. Unlocking the mysteries of dark matter and dark energy is a major focus of current efforts in cosmology.

University of Pittsburgh cosmologists are attacking these fundamental cosmological questions from a number of angles. The various collaborative surveys that involve members of the University of Pittsburgh group provide insights. Data on the distances of Type Ia supernovae are used to study the expansion history of the universe, which in turn probes the properties of dark energy.  Efforts to understand the nature of Type Ia Supernova progenitors and their evolution through cosmological time scales are also a key ingredient to unravel the dark energy mystery. The Atacama Cosmology Telescope (ACT), which observes the CMB sky from the Chilean Andes, aims to detect thousands of galaxy clusters through their Sunyaev-Zeldovich distortion of CMB. The abundance of the clusters will probe the physics of dark energy and dark matter. Observational and theoretical programs under development will enable future facilities such as Pan-STARRS, the Dark Energy Survey (DES), LSST, and the Joint Dark Energy Mission (JDEM) to probe the nature of dark energy using a variety of techniques, including gravitational lensing, galaxy clustering, supernovae distances, and baryon acoustic oscillations. The nature of dark matter also can be explored with these methods. The implications of specific dark matter theories for experiments such as the Fermi Gamma-Ray Telescope (formerly GLAST) and terrestrial experiments that aim to “catch” dark matter particles as they stream through the Earth on their voyage through the Galaxy, also are being studied. Finally, members of the group continue to foster classroom activities and outreach at the nearby Allegheny Observatory. For nearly a century, the Allegheny Observatory has been one of the premier facilities in the world for ground-based astrometry. From 1977 to 2008, it was under the directorship of Professor Emeritus George Gatewood.