The astronomy, gravitation and cosmology group is among the nation’s largest and most active with twelve participating researchers. These include seven current faculty (Patrick Brady, Philip Chang, Jolien Creighton, Dawn Erb, David Kaplan, Xavier Siemens, and Alan Wiseman), two Distinguished Professors Emeriti (John Friedman and Leonard Parker), two Adjunct Professors (Bruce Allen and Luis Anchordorqui), and one Visiting Scientist (Maria Alessandra Papa). The researchers are joined in their endeavors by several postdoctoral research associates, as well as graduate and undergraduate students. More details can be obtained from web pages of individual group members and from other areas of the Physics Department website.

## Leonard E Parker Center for Gravitation, Cosmology and Astrophysics

At the **Leonard E Parker Center for Gravitation, Cosmology and Astrophysics**, we push the frontiers of astrophysics through the novel use of observation, theory, and computation. By bringing together expertise in gravitational physics, astrophysics, and computing, we can address scientific challenges in relativistic astrophysics, gravitational-wave astronomy, particle astrophysics, cosmology, and quantum gravity. Research at the Center addresses problems in relativistic astrophysics, numerical relativity, gravitational-wave astronomy, cosmic-ray astrophysics, cosmology, neutrino astronomy, quantum fields in curved space-time, and quantum gravity.

## Faculty Research

**Patrick Brady’s **research interests include the dynamics of gravitational collapse, black holes, numerical relativity including simulation of binary coalescence, and the detection of gravitational waves using interferometric gravitational-wave detectors. In broad terms, he is interested in theoretical and experimental aspects of gravitation and gravitational-wave astronomy.

*For more information:* **Brady’s Research Website**

**Philip Chang’s** research interests include supernovae, compact objects, disk dynamics, plasma astrophysics, and turbulent star formation. In general terms, he is interested in various aspects of theoretical astrophysics and cosmology.

*For more information:* **Chang’s Research Website**

**Jolien Creighton’s** research concerns the portion of Einstein’s theory of General Relativity, where gravity is described in terms of geometry: the distances between points in space and time. Gravitational waves—oscillating gravitational fields that affect the distances between nearby points—are produced by the most violent events in our universe including supernovae, collisions of black holes, and the big bang. Yet, these waves are barely noticeable and have yet to be detected.

The Laser Interferometric Gravitational-Wave Observatory, LIGO, is a national facility to detect gravitational waves. Creighton participates in the LIGO Scientific Collaboration in an international effort that will search for gravitational waves from the distant universe.

*For more information:* **Creighton’s Research Website**

**Dawn Erb’s** research interests include galaxy formation and evolution, the kinematics, chemical evolution and stellar populations of galaxies at high redshift, feedback processes in starburst galaxies, and the evolution of the intergalactic medium at high redshift.

*For more information:* **Erb’s Research Website**

**John Friedman** has worked on a variety of problems in gravitational physics, involving neutron stars, black holes and gravitational collapse, the topology of spacetime, and topological questions in quantum gravity.

**David Kaplan’s** research concerns multi-wavelength (radio, infrared, optical, X-ray) observations of a variety of types of young neutron stars such as isolated, thermally emitting neutron stars and magnetars. He is also working on detecting radio transients with the Murchison Widefield Array and the Australia Square Kilometre Array Pathfinder

*For more information:* **Kaplan’s Research Website**

**Leonard Parker** was the first to show that quantum field theory implies particle creation in curved spacetimes. This process creates particles and amplifies small perturbations in an expanding universe. The observed features of the cosmic microwave background (CMB) radiation and of the large-scale structure of the present universe confirm that this particle creation process in an in inflationary universe was responsible for the CMB temperature anisotropies and for the clumping of matter that gave rise to galaxies and galactic clusters.

Parker was first (with S. A. Fulling) to develop the method of adiabatic regularization in curved spacetime. He was also first to calculate the perturbations of the spectra of one-electron atoms in arbitrary gravitational fields in terms of the Riemann tensor.

**Xavier Siemens’** research is focused mostly in gravity wave astrophysics, early universe cosmology, especially cosmic strings, and biophysics. He also works on calibration of LIGO data, which is experimental work.

*For more information:* **Siemens’ Research Website**

**Alan Wiseman’s** research is in the area of general relativity and gravitation with a special emphasis in gravitational-wave generation and detection. He has published a number of papers involving computations of the expected gravitational-wave signals from inspiraling binary star systems using post-Newtonian theory. He also works in the area of black hole perturbation theory and the radiation reaction problem in curved space time.

*For more information:* **Wiseman’s Research Website**