Research on Gravitational Waves and Compact Binaries

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The exciting observations by the LIGO and Virgo detectors of merging neutron stars and stellar-mass black holes over the past several years have opened up the era of gravitational wave astronomy. These events have revealed new astrophysics, including confirming the process through which heavy elements are created and discovering a new class of heavy stellar-mass black holes, and are providing novel tests of general relativity theory. They also herald eventual gravitational wave observations of extreme-mass-ratio inspirals (EMRIs), where a stellar-mass black hole or neutron star spirals into a supermassive black hole, such as those now known to exist in the center of virtually all large galaxies. Surrounded by dense star clusters, these supermassive black holes will frequently capture compact stars (e.g., neutrons stars or stellar mass black holes) into highly eccentric orbits. As these compact stars orbit, they radiate gravitational waves, causing the orbit to decay and the compact object to eventually be swallowed by the supermassive black hole. The emitted gravitational radiation is potentially observable with LISA, the future space-based gravitational wave detector. The theoretical work funded by this award will provide improved predictions of the expected signals from highly-eccentric compact merging binaries. Detection of gravitational waves from such EMRIs will provide unique strong field tests of gravity and probe the nature of black holes.To pursue this effort, development of new techniques in black hole perturbation theory and gravitational self-force methods will be made, along with writing associated advanced computer codes. High precision results from perturbation theory and self-force calculations will be studied to uncover high-order terms in the post-Newtonian expansion of eccentric binary motion and associated gravitational wave emission. Perturbation theory and self-force findings in the extreme-mass-ratio, post-Newtonian overlap region support and reinforce broader efforts to advance post-Newtonian theory to higher orders and provide calibrations for effective-one-body models of merging binaries. The PI's group is extending self-force calculations to generic motion on Kerr backgrounds, using a scalar field model initially, with primary focus to make these computations more efficient. New self-force techniques will be combined with osculating elements codes to build long-term inspiral models for eccentric EMRIs. Some parts of this work will be conducted in external collaboration with several former students and with colleagues at University College Dublin. Numerical and analytic results, as well as some computer codes, will be made available online.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.