Binary Black Holes at the Extremes in the Era of Gravitational Wave Astronomy

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This award supports research in gravitational wave detector data analysis and it addresses the priority areas of NSF's "Windows on the Universe" Big Idea. This research project is devoted to the analysis and modeling of gravitational waves. These ripples in the very fabric of space and time are produced when the densest objects in the Universe -- such as black holes and neutron stars -- orbit and collide. The detection of gravitational waves by the NSF-funded LIGO and European Virgo collaborations has opened up a new window on the Universe, revealing previously invisible events like pairs of black holes merging. Members of the Austin Relativity group will participate in the analysis of gravitational waves as members of the LIGO collaboration, helping to infer the properties of the sources of these ripples. To ensure the maximum scientific benefit from the detection of gravitational waves, models for how these waves are produced require continuing refinement. Members of the research group will perform numerical simulations on supercomputers in order to explore the orbit and collision of pairs of black holes. The focus will be on extreme configurations -- such as systems with very unequal masses and complicated orbits -- with the goal of making new connections to pen and paper approximations for how gravitational waves are produced in these cases. These research activities will provide training for graduate students in high-performance computing and data analysis, skillsets which are in great demand and of great benefit to society. In addition, members of the group will engage in outreach activities in order to educate and inspire the public about this new field of physics and astronomy. Finally, members of the group will participate in outreach to high school women, in order to promote diversity within STEM fields.This project focuses on the study of binary black holes with significantly different masses, whose gravitational waves are challenging to model. This project will connect numerical simulations of these binaries with analytical approximations which are capable of modeling binaries with very unequal masses, in particular the self-force approximation. Targeted simulations will test the self-force and other approximations, provide independent verification of their predictions, reveal their limitations, and point to refined approaches for use in GW science. The key tool for making comparisons will be invariant quantities, such as the redshift factor and orbital frequency shifts of the black holes. Advances in modeling these binaries will have immediate benefits for the current era of GW detectors, and will be crucial for the success of future, space-based missions. In addition, the PI and other members of the research group will directly participate in the analysis of gravitational waves. Members of the group measure the properties of these binaries which produce these waves using Bayesian parameter estimation. These inferences are a crucial first step in the use of gravitational wave detections for understanding the population of binary black holes, inferring the nuclear equation of state from observations of binary neutron stars, testing the theory of relativity, and using gravitational waves to measure cosmic expansion.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.