Dynamical and Strong-Field Gravitational-Wave Phenomenology

The NSF's Laser Interferometer Gravitational-Wave Observatory (LIGO) and collaborating facilities observed gravitational waves from nearly one hundred merging black holes and neutron stars. These remarkable measurements opened a new field of gravitational-wave astrophysics, which is allowing gravity to be studied in new ways. To interpret the results of these observations and learn about Einstein's general relativity, the underlying theory of gravity that describes these waves, precise calculations must be carried out of the gravitational waves that are emitted during the merger of two black holes. This award supports a research effort that combines first-principles calculations, data-analysis procedures, and analytical and numerical modeling of black holes, which will be used to extract 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 award will be short essays about the general themes of black holes and gravitational waves, to help introduce these subjects to a wider audience of fiction and non-fiction readers. The writings will be free to read on the research website of the PI. More specifically, the goals of this project will be to make advances in gravitational physics in several directions. (i) The PI and students will compute persistent gravitational-wave signals from binary black holes using consistency relations determined from recently identified conservation laws in asymptotically flat spacetimes; the detection prospects of these signals will be assessed. (ii) They will model the waves of the persistent observable called the gravitational-wave memory, which has the best chance of being detected from binary mergers. With their improved model, they will reassess the significance of the memory effect in the observed black-hole mergers. (iii) They will improve the computation of gravitational waves emitted from black-hole binaries with large mass ratios that are surrounded by dense distributions of dark matter. The dark matter and its interaction with the binary will be modeled more accurately, which will help produce smaller biases in the data analysis and parameter estimation forecasts. (iv) They will develop gravitational waveforms for mergers of black holes in modifications of Einstein’s theory that cover all the stages of the merger process. These approximate waveforms can help reveal a simpler picture of the more complicated phenomenology of the merger and could be used in gravitational-wave tests of general relativity. 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.