NSF-BSF: Gravitational Waves From Compact Objects at Galactic Nuclei

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Recent direct detections of gravitational waves (GW) from merging binary black holes by the LIGO and Virgo GW detectors have transformed the way astronomers observe and understand the Universe. However, it is still an open question how these pairs of compact objects like black holes come together and get close enough to merge. One important channel is dynamical formation in dense star clusters. A research collaboration between the University of California-Los Angeles and the Hebrew University of Jerusalem in Israel will examine the formation, evolution, and gravitational wave emission of systems composed of compact object binaries in galactic nuclei , or the central regions of galaxies, which host some of the densest known stellar clusters in the universe. The project will include graduate and undergraduate students in the research. Additionally, the UCLA lead investigator will implement an original educational workshop, entitled ``California’s fUtuRe scIence lEaders (CURIE), PHysics & AStronomy for EveRyone (PHASOR)." This educational workshop is aimed at under-represented minority high schoolers in Los Angeles and will directly impact young students, showing them that STEM career paths are open to them. Expanding on a proof-of-concept study that outlined the possible GW sources in dense galactic cores, the researchers will analyze the physical processes that can either lead to or suppress the merger of compact objects. The work will include gravitational interactions between stars and the supermassive black hole (SMBH) at the galaxy center, general relativity, gravitational wave emission, and post-main sequence stellar evolution. The methodology will utilize a combined approach of secular (i.e., long-term, orbit averaged) and statistical approaches of the many-body interaction, as well as direct integration (i.e., N-body) effects. In particular, the SMBH can induce collisions and mergers between stars and compact objects, such as black holes and neutron stars. The study will predict the outcome of the dynamical formation of GW sources at galactic nuclei in the context of LIGO-Virgo and LISA observations and use the results to attempt to explain some of the exotic GW signals, such as the puzzling massive compact objects (e.g., GW190814 and GW190521). This project advances the goals of the NSF Windows on the Universe Big Idea.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.