Relativistic Gravitation and Astrophysics

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Within the next decade the likely detection of gravitational waves from astrophysicalsources will open a new window for astronomy and provide new tests of Einstein's theoryof general relativity. Interpreting the observations will require accurate theoretical gravi-tational waveforms calculated from the theory. This project will endeavor to provide theneeded 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 speedsof the source bodies and of light, respectively. The goal will be to find the equations ofmotion for the bodies correct to order (v/c)7 beyond Newtonian gravity, and the flux ofgravitational radiation to order (v/c)6 beyond the lowest "quadrupole" approximation. Thiswill 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 alsobe 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 bestudied. 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 thegraviton has a mass by observing waves from inspiral of pairs of supermassive black holesusing the proposed space-based gravitational antenna, LISA. A recently published class ofalternative 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 asguides to other possible tests of a massive graviton.