Gravitation and Relativistic Astrophysics

University Of Wisconsin-Milwaukee, Milwaukee WI

Investigators

Abstract

This award supports research on two major projects. The first is gravitational-wave astronomy from inspiral of double neutron-star (NS-NS) systems and black-hole-neutron-star (BH-NS) systems. One goal is to use gravitational wave observations from binary inspirals to measure parameters of the neutron-star equation of state (EOS). A collaboration with three numerical relativity groups will compute the gravitational waves produced in the late inspiral of double neutron-star systems, use the waveforms to analyze the way in which gravitational- wave observations will constrain the equation of state of cold matter above nuclear density, and find the accuracy with which equation-of-state and neutron-star parameters can be extracted. The study of BH-NS inspiral is still in its early stage, with the wide range of black hole masses and spins still to be explored. Computer simulations will explore the late inspiral and merger of systems with varying mass ratios and black hole spins, including spins oblique to the orbital plane. The second project will examine extreme-mass-ratio-inspiral (EMRI). A principal goal of the planned NASA/ESA space-based gravitational wave observatory, LISA, is to observe gravitational waves from the inspiral of stellar-size black holes orbiting supermassive black holes (the EMRIs). To maximize the number of observed events and, more critically, to extract from the observations the characteristics of the sources, it is essential to obtain accurate waveforms associated with generic orbits. Because the ratio of the component masses is small, the orbits and gravitational waves from these binary systems can be described to high accuracy by a perturbative expansion. Finding the conservative part of the self force, a correction needed for parameter extraction, may be the most difficult part of the problem, but it can be regarded as a correction to an inspiral described by the dissipative radiation-reaction force on a particle in near-geodesic orbit. Understanding the waveforms from binary inspiral and their implications for gravitational-wave astronomy is a critical part of the nation's substantial commitment to the LIGO and to the planned space-based observatory, LISA. With support from funds from the University of Wisconsin-Milwaukee's Research Growth Initiative, from a University Scholarship, and from the present NSF grant, graduate students and a post-doctoral research associate will gain expertise in areas of gravitational physics, relativistic astrophysics, and numerical relativity that will be fundamental to the development of gravitational-wave astronomy.