Collaborative Research: Understanding Compact Binary Formation With Gravitational Wave Observations

The Laser Interferometer Gravitational-Wave Observatory (LIGO) in the US and the Virgo detector in Europe have ushered in a new era in the exploration of the Universe. These observations have resolved old puzzles in physics and astronomy, and they have revealed a new population of astronomical objects. LIGO and Virgo with upgraded sensitivities and new detectors will soon observe a much larger catalog of sources. This research program has two goals. The first is to use the catalog of events from the upcoming observing runs to better understand how compact binaries form and merge. The second is to study how gravitational waves can be used to study the early Universe, measure its expansion rate, and infer the properties of dark matter particles. The program’s investigators will educate students in Centre County, PA and in the Baltimore area through lectures and demonstrations at schools, summer camps, and internships. They will continue to organize the successful "Physics and Astrophysics at the Extreme" (PAX) series of workshops. In addition, they will initiate a new series of workshops on the populations of compact objects discovered by LIGO, Virgo and KAGRA: "Gravitational wave populations: what's next?" (or "POPX").Since the discovery of compact binary mergers by LIGO and Virgo, astrophysicists have explored several different formation scenarios. A catalog of merger events with precisely measured masses, spins and redshifts is critical to infer how often compact binaries merge, how they form, and their redshift evolution. Moreover, compact binary sources can provide accurate distance measurements. Together with the redshift from electromagnetic observation of their hosts, this is a new tool for deducing the expansion rate of the Universe. Over the past two decades, the members of this team have pioneered methods to address these problems and have developed tools that have been made public. This program will use the larger gravitational-wave catalogs from the next two observing runs of LIGO, Virgo and KAGRA to address unsolved problems in astrophysics and cosmology. The investigators will implement astrophysical spin models in population synthesis for field binaries. They will develop rapid, consistent models of dynamical formation channels, compare tools for population inference, and study how waveform systematics affect gravitational-wave astronomy. The proposal will also study stochastic foregrounds of compact binary systems and their effect on model inference. It will harness gravitational-wave observations to resolve the Hubble tension, and explore the properties of dark matter and primordial black holes.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.