Relativistic Gravitation and Astrophysics

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Since the first detection of gravitational waves from merging black holes in 2015, gravitational-wave science has emerged as a new and vibrant branch of astronomy. In addition to opening new avenues for exploration, such as the origin of cosmic black holes, it has yielded new tests of Einstein’s general theory of relativity. Observations by astronomers of the motions of stars and gas near supermassive black holes, such as the one at the center of the Milky Way, have also opened the possibility of testing Einstein’s theory in realms where the warping of spacetime is extreme, and raised questions about how stars form and evolve near such extreme objects. Yet in order to test Einstein’s great theory, it is essential to know what it actually predicts for real measurements. This project continues a program of research to provide concrete links between the abstract beauty and complex mathematics of Einstein’s theory and the real world where measurements are made by physicists and astronomers. These links are established by finding approximate, yet accurate solutions of the equations in forms that are practical and usable. The outcomes of this research will be used by data experts at the gravitational-wave observatories to perform better tests of general relativity using newly detected signals, and will be used by astronomers to probe how general relativity affects complex systems such as stars orbiting supermassive black holes, or three-body systems involving bodies ranging from black holes to exoplanets. Einstein's theory is a topic that fascinates the general public, and the PI will continue to give public lectures on topics related to this research, bringing understanding of Einstein's ideas to the broader community.Specifically, this project will contribute to the ability of ground-based gravitational-wave observatories such as the LIGO-Virgo-Kagra network to test general relativity, by computing the gravitational waves emitted by binary systems as predicted by an important alternative theory, known as Einstein-Aether gravity, to high accuracy in the so-called post-Newtonian approximation. The project will continue to extend recent work of the PI on incorporating the effects of Einstein’s theory into the dynamics of three-body systems, such as a binary-black-hole system in a galactic core with a supermassive black hole at its center. A specific goal is to see whether observations of the star known as SO-2 which revolves around the galactic center black hole can be used to detect or limit a hypothetical intermediate-mass black hole in orbit around the supermassive object. Another project is to study general relativistic effects in N-body systems at the second-post-Newtonian approximation, with the goal of assessing how relativistic effects impact the long-term stability of dense stellar systems.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.