Research on Gravitational Waves and Compact Binaries

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This award will support research on the dynamics and gravitational wave emission of compact binary systems in general relativity. The numerous observations by LIGO and Virgo of merging stellar mass black holes and neutron stars over the last five years have opened up the era of gravitational wave astronomy. These events reveal new astrophysics, including confirming the site of heavy element formation, discovering a new class of intermediate mass black holes, and providing novel tests of general relativity theory. These observations also motivate development of the LISA space-based detector and raise prospects for eventual gravitational wave observations of extreme-mass-ratio inspirals (EMRIs). EMRIs involve a stellar-mass black hole (or neutron star or white dwarf) spiraling into a supermassive black hole (which are 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 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 (or potentially tidally disrupted in the case of white dwarfs). The emitted gravitational radiation will be observable with LISA. The theoretical work funded by this award will provide improved predictions of the expected signals from highly-eccentric compact merging binaries. The US is a leader in gravitational wave astronomy and these theoretical activities support future extensions of such observations. Detection of gravitational waves from EMRIs will provide unique strong field tests of gravity and probe the nature of black holes, while also uncovering astrophysical properties of the dense central regions of galaxies.To pursue this effort, development will be made of new techniques in black hole perturbation theory and gravitational self-force methods, along with writing associated advanced computer codes. Symbolic mathematical calculations of black hole perturbation theory and the gravitational self-force will be made to high order in the post-Newtonian (PN) expansion for eccentric EMRIs. These calculations will be extended to EMRIs with general orbits about a rotating (Kerr) primary. These high PN order perturbation and self-force findings support and reinforce broader efforts to advance PN theory and provide calibrations of effective-one-body models of merging binaries. The PI's group draws upon their experience in recent years with a fully symbolic code that was specialized to Schwarzschild EMRIs to now write a fully symbolic code for Kerr EMRIs. Generated gravitational wave flux and self-force data will be incorporated in adiabatic and post-adiabatic inspiral calculations to provide accurate waveforms for much of an EMRI's evolution. Some parts of this work will be conducted in collaboration with former students and with colleagues at University College Dublin. Results and 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.