ABSTRACT

This award supports research in relativity and relativistic astrophysics, and it addresses the priority areas of NSF's "Windows on the Universe" Big Idea. Gravitational-wave (GW) physics and astronomy has entered a new era: GW transient events (so far, from the merger of compact binary systems containing black holes and/or neutron stars) detected with the LIGO and Virgo detectors in their first three observing runs (O1, O2, O3) are frequent. In the fourth observing run (O4), estimated to begin in December 2022 and continuing for one year, the KAGRA detector will also participate, and the LIGO and Virgo detectors will have increased sensitivity to distant sources. This will result in unprecedented rates of discovery of GWs from compact binary mergers, and the potential for many discoveries of GWs from other astrophysical sources such as a stochastic GW background. Indeed, entirely new classes of GW sources may be discovered. These observations will enable a wealth of studies, ranging from fundamental physics to astronomy, astrophysics and cosmology. Observations of binary black hole mergers are used to understand stellar evolution and the formation, evolution and death of binaries. They enable uniquely powerful tests of general relativity in the strong-field, highly-dynamical regime of gravity. Observations of binary neutron star mergers enable constraints on the nuclear equation of state, unique measurements of the local Hubble-Lemaitre parameter, and insights into the origins of element formation in the universe. The proposed work, in coordination with the LIGO Laboratory and LIGO, Virgo and KAGRA (LVK) Collaborations, focuses on the development of methods to confidently identify weak GW signals from astrophysical sources in the noisy data, using highly optimized search pipelines, and interpret the results in their astrophysical context. These methods will be further developed and applied to data from the LVK O4 run, and lessons learned will be incorporated into appropriate preparation for future observing runs. A variety of activities involving students and teachers from local middle and high schools, mentoring summer undergraduate research fellows, and organizing and participating in GW Open Data Workshops, aim to make these advances in gravitational wave science accessible to a broad range of people and groups.

This work is devoted to discovering and analyzing gravitational-wave (GW) signals in the LIGO, Virgo and KAGRA detectors during FY2023-FY2025 (LIGO's observing runs O4 and O5). Specific scientific goals are: (a) Identifying GW signals from compact binary mergers in data from LIGO, Virgo, and KAGRA, using two of the LSC "flagship" search pipelines, PyCBC and gstlal; (b) performing ever more sensitive Tests of General Relativity as the theory of strong-field gravity governing binary black hole (BBH) mergers, through searches for post-merger GW "echoes", searches for non-tensorial polarizations in GWs from CBCs, and searches for beyond-GR parameters in signal waveforms from BBH mergers; (c) performing ever deeper searches for strong gravitational lensing of GW signals from compact binary mergers - the identification of GW event pairs, including sub-threshold event candidates, and joint parameter estimation; (d) improving the efficiency and robustness of single-event astrophysical parameter estimation to infer the masses and spins of the compact objects with accuracy and precision; and (e) using the much larger event count from O4 and O5 to further develop our understanding of the BBH merger rate as a function of mass, spin, and cosmological redshift. The work will build on existing expertise and experience in all of these efforts, and extend them to the era of frequent detections by automating routine tasks. The results of these efforts will make it possible to make confident detections of GW events as they become frequent, and make the information obtained available to the LSC, to the astronomical community, and to the public, promptly, so that they can be fully exploited by those communities to advance gravitational-wave astronomy. In order to make gravitational wave science accessible to a broad range of people and groups, the following activities will be pursued: training and mentoring a diverse range of undergraduate students in the LIGO SURF/REU program; supporting open science through the GW Open Science Center; organizing and participating in annual GW Open Data Workshops; using scientific computing as a tool to engage high school and undergraduate students through online tutorials and through outreach to STEM teachers at local schools; and engaging in K-12 outreach and communicating with the general public, through visits to local middle- and high-school STEM fairs and classrooms.

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.

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