Relativistic Gravitation and Astrophysics

Washington University, Saint Louis MO

Investigators

Abstract

Within the next decade the likely detection of gravitational waves from astrophysical sources will open a new window for astronomy and provide new tests of Einstein's theory of general relativity. Interpreting the observations will require accurate theoretical gravi- tational waveforms calculated from the theory. This project will endeavor to provide the needed waveforms, by solving Einstein's equations systematically in a post-Newtonian ap- proximation, which amounts to an expansion in powers of v/c, where v and c are the speeds of the source bodies and of light, respectively. The goal will be to find the equations of motion for the bodies correct to order (v/c)7 beyond Newtonian gravity, and the flux of gravitational radiation to order (v/c)6 beyond the lowest "quadrupole" approximation. This will make use of a method known as Direct Integration of the Relaxed Einstein Equations (DIRE), that has been developed at Washington University. Using this method it will also be possible to study the effects of the interior structure of the bodies, including their spin, on the motion and gravitational waveform, to high order in the post-Newtonian expansion. Ways to use gravitational-wave data to test alternative theories of gravity will also be studied. This includes testing the scalar-tensor alternative theories by observing gravita- tional waves from neutron stars inspiralling into black holes, and testing whether or not the graviton has a mass by observing waves from inspiral of pairs of supermassive black holes using the proposed space-based gravitational antenna, LISA. A recently published class of alternative theories of gravity that predict a massive graviton will be studied in detail as "foils" against which to compare and contrast the predictions of general relativity, and as guides to other possible tests of a massive graviton.