Gravitational Wave Physics and Astrophysics with LIGO

Gravitational-wave (GW) physics and astronomy have entered a new era: GW transient events detected with the LIGO and Virgo detectors in their first four observing runs (O1, O2, O3, and O4) are frequent. So far, they are all from compact binary coalescing (CBC) systems containing merging black holes and/or neutron stars. The fourth observing run (O4) is planned to continue through November 2025. This is resulting in increased rates of discovery of GWs from compact binary mergers, including the potential for rare and exceptional events with high black hole spins, spin-induced orbital precession, and/or eccentric orbits - all of which give crucial clues to the formation of compact binaries in astrophysical environments. There is the potential for many discoveries of GWs from other astrophysical sources such as GW bursts that are not well modeled by templates derived from General Relativity; 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. The PI's team, working with the LIGO Laboratory and LIGO, Virgo, and KAGRA (LVK) Collaborations, develops methods to confidently identify weak GW signals from astrophysical sources in the noisy detector data and interpret the results in meaningful ways. The project will further develop and employ these methods using data from the LVK O4 run. The team will be deeply involved in the assembly of the fifth and sixth GW Transient Catalog (GWTC-5 and 6) covering the last 2/3 of data from O4, robust analysis of individual events with Bayesian parameter estimation, and identification of exceptional events that may not fit into the overall population of events observed so far. We will work with the LVK to present these results in publications that will be foundational in the fields of GW physics and astronomy. During the period covered by this award, the PI will continue and deepen their efforts towards making their science accessible to a broad range of people and groups, through the following activities: conducting a GW science study group for undergraduates throughout the academic year, including weekly meetings and lectures as well as research project mentorship, with participants from Caltech, Pasadena Community College, and other local colleges and universities; mentoring students in the LIGO Summer Undergraduate Research Fellowship (SURF/REU) program; training undergraduate research students in scientific computing and GW data analysis in GW Open Science Center (GWOSC) Open Data Workshops; and supporting open science through the GW Open Science Center. The project focuses on the identification of rare and exceptional events in the GW Transient Catalog of confidently detected binary black hole (BBH) mergers, which may have significant spin-induced orbital precession and measurable eccentricity in the LIGO-Virgo frequency band. The team will work to extend GW waveform models derived from numerical relativity to include all the relevant physics, including (for the first time) eccentric orbits. The team will apply Bayesian parameter estimation to promising detected events, developing robust methods to identify events with significant precession and/or eccentricity, and explore whether they form a distinct population beyond what has been observed so far. The team will search for BBH events with eccentricity using both modeled waveform templates and "model-informed" GW burst methods, and contribute to the search for BBH and other short-duration GW bursts in O4 data (offline) with burst methods. These activities broaden the discovery space of GW sources and are among the most important and urgent frontiers in GW astrophysics. The goal is to have advanced methods in place and in use for the fifth observing run (O5), planned to begin in early 2028. 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.