Gravitational Waves from Neutron Star and Black Hole Mergers

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The first direct detection of gravitational waves in 2015 was ahistoric breakthrough in gravitational physics. The first signals wereidentified as merger events of two black holes, which demonstratedthat mergers of compact binaries are indeed primary candidates forgravitational wave sources. The focus of the proposal is on compactbinaries involving neutron stars, either in a neutron star binary or abinary formed by a neutron star and a black hole, which are describedby general relativity coupled to general relativistic hydrodynamics.The data analysis and parameter estimation for merger events rely onnumerical simulations that solve the two-body problem of Einstein'sgeneral theory of relativity in the highly-dynamic strong-fieldregime. The goal is to provide theoretical models for the relativisticdynamics, the merger process with ejecta and torus formation, and thegeneration of gravitational waves. So far, the system that has beenpredominantly studied in numerical relativity is non-spinning neutronstars of equal or comparable mass on quasi-circular orbits. In recentwork technical limitations in constructing general relativistic datafor spinning neutron stars in binaries were resolved. The main goal of theproject is to greatly extend the first proof-of-principle calculationswith spin. By varying the spins, masses and eccentricity of thebinary, the long-term goal is to thereby complete the gravitationalparameter space accessible to numerical relativity and to prepare forthe corresponding gravitational wave observations that are expected inthe near future.