Relativistic Gravitation and Astrophysics

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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 and advancing this new field will require accurate theoretical predictions for the wave signal from a given source. This project will make use of a method known as Direct Integration of the Relaxed Einstein Equations (DIRE), that has been developed by the PI and his students at Washington University, which solves Einstein's equations systematically in a procedure known as the post-Newtonian approximation (appropriate for systems where the velocities are small compared to the speed of light). Using this method, it will be possible to study the detailed motion and radiation from the inspiral of compact binary systems (double star systems containing neutron stars or black holes) to a high degree of accuracy. Post-Newtonian methods will also be used to study unusual aspects of the curved spacetime surrounding rotating black holes, related to the existence of the so-called "Carter" constant of the motion, and to calculate the recoil velocity experienced by black holes formed from compact binary merger. Ways to use gravitational-wave data to test alternative theories of gravity in new regimes and to measure astrophysical and cosmological parameters will also be studied. In particular, a detailed analysis of gravitational radiation from compact binary inspiral in a class of "scalar-tensor" alternatives to general relativity will be carried out, together with a study of data analysis strategies for placing the best possible bound on this class of theories. The possibility of testing general relativity in the strong-field vicinity of the massive black hole in the center of our galaxy using future adaptive optics infrared interferometry will be analyzed by studying orbital perturbations of stars in close orbits near the hole caused by other stars in the central region, by a possible distribution of dark matter, and by tidal distortions of the stars. This will involve a mixture of analytical post-Newtonian calculations and numerical N- body simulations.The work on equations of motion, gravitational waveforms and analysis of gravitational-wave data will impact the emerging field of gravitational-wave astronomy. The work on recoil velocities may contribute important insights that could impact astrophysical modeling of the growth of massive black holes in galaxies, as well as the interface between post-Newtonian theory and numerical relativity. The work on testing general relativity near the galactic center black hole could impact the development of advanced instrumentation for observational infrared astronomy. Education and training of students will be integrated into the research program.