Dynamical and Strong-Gravity Effects from Black-Hole Binaries

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The NSF's Laser Interferometer Gravitational-Wave Observatory (LIGO) and the Virgo detector have now observed gravitational waves from tens of pairs of merging black holes and neutron stars. These remarkable observations have opened up a new field of gravitational-wave astrophysics, and they are allowing the predictions of Einstein's theory of relativity to be tested in new ways for these dynamic and strongly gravitating binaries. Much remains to be learned from these novel observations. Through a better understanding of the predictions of Einstein's theory and through more precise calculations of the emitted gravitational waves, more of the scientific potential of these observations will be tapped. This project, therefore, outlines a research program to use a combination of foundational computations, as well as analytical and numerical modeling of black holes and neutron stars, to aid in extracting insights from gravitational-wave observations. Many of the calculations will be carried out by graduate students, who will be trained in techniques that are useful in physics research and other quantitative areas. A final component of the project involves the development of visualizations that are intended for a broad audience of non-scientists, which aim to make the generation of gravitational waves more intuitive and accessible.More specifically, the research goals of this project will be to make advances in gravitational physics on two fronts: (i) to investigate and compute the part of the gravitational waveform that is strongly constrained by the symmetries and conserved quantities of isolated radiating systems, and (ii) to compute gravitational waveforms from a range of black-hole binaries that can be used to look for deviations from relativity because of the presence of matter or the modification of the underlying gravitational theory. The main goals of direction (i) are first, to compute gravitational waveforms associated with gravitational-wave memory effects that can be evaluated rapidly; second, to understand discrepancies between two commonly used definitions of angular momentum in asymptotically flat spacetimes; and third, to compute generalized notions of memory effects in these spacetimes. For direction (ii), there are three different objectives: for the first, investigating the influence of dense distributions of matter on the gravitational waveforms from black-hole binaries with mass ratios that differ greatly from one; for the second, to explore how modifications to general relativity affect the gravitational-wave memory effect; and for the last, approximating the gravitational waveform in modified gravity theories using a combination of perturbative expansions. The outreach aims of this project revolve around creating visualizations of the warped spacetime of binaries radiating gravitational waves. The visualizations will highlight the physical stretching and squeezing effects of gravitational waves and illustrate how gravitational waves are generated. Animations of these visualizations will be posted online and could also be used as pedagogical tools.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.