Gravitational Wave Models for Black Hole - Neutron Stars in General Relativity and Beyond

This award supports research in relativity and relativistic astrophysics, and it addresses the priority areas of NSF's "Windows on the Universe" Big Idea. The 2015 Nobel prize-winning observation of gravitational waves from a binary black hole merger by the LIGO detectors unveiled an entirely new window to the universe. This was followed up by the groundbreaking observations of binary neutron star and black hole-neutron star mergers. One of the key goals of gravitational wave astronomy is to test Einstein’s general relativity under the extreme conditions of these mergers, where new physics like quantum gravity effects can become important. The main objective of this project is to develop novel numerical simulations and data-driven models that are critical for conducting these tests and help maximize the scientific impact of gravitational wave observations. This project includes support for students as well as outreach components at local schools and observatories, thereby contributing directly to mentorship, recruitment, and retention in an emerging STEM area. The computational skills gained by the students are applicable in broader areas like data science and machine learning, preparing them for a wide range of successful careers in academia and industry. This award is about the development of numerical simulations and models that predict the gravitational wave signals from black hole-neutron star and binary neutron star mergers, both in general relativity and alternative theories. As our gravitational wave detectors continue to improve, there is a need to improve our gravitational wave models that are used to compare against the observed data and to test general relativity in the strong field regime. This research addresses this pressing need by conducting novel numerical simulations of black hole-neutron star and binary neutron star mergers in general relativity as well as alternative theories like scalar-tensor gravity. This is followed by the construction of data-driven surrogate models that accurately reproduce the gravitational wave signal from the simulations. Such simulations and models are critical for reliably extracting the astrophysical source properties and testing general relativity using these observations. 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.