General Relativistic Black Hole-Neutron Star Simulations: Effects of Black Hole Spin and Binary Mass Ratio

86 p.Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 2009.BHNS mergers are candidate engines for generating both short-hard gamma-ray bursts (SGRBs) and detectable gravitational waves. Using our most recent conformal thin-sandwich BHNS initial data (quasicircular binaries representing quasiequilbrium solutions to Einstein's initial value equations) and our fully general relativistic hydrodynamics code, which is now capable of adaptive-mesh refinement (AMR), we are able to efficiently and accurately simulate these binaries for multiple orbits through inspiral, merger, and ringdown. We evolve the metric using the Baumgarte-Shapiro-Shibata-Nakamura (BSSN) formulation with the standard moving puncture gauge conditions and handle the hydrodynamics with a high-resolution shock-capturing scheme. We explore the effects of BH spin (aligned and anti-aligned with the orbital angular momentum) by evolving three sets of initial data with BH:NS mass ratio q = 3: the data sets are nearly identical, except the BH spin is varied between a/MBH = -0.5 (anti-aligned), 0.0, and 0.75. The number of orbits before merger increases with a/MBH, as expected. We also study the nonspinning BH case in more detail, varying q between 1, 3, and 5. We calculate gravitational waveforms for the cases we simulate and compare them to binary black-hole waveforms. Only a small disk (< 0.01 M&odot; ) forms for the anti-aligned spin case (a/MBH = -0.5) and for the most extreme mass ratio case (q = 5). By contrast, a massive (Mdisk &ap; 0.2 M&odot; ), hot disk forms in the rapidly spinning (a/M BH = 0.75) aligned BH case. Such a disk could drive a SGRB, possibly by, e.g., producing a copious flux of neutrino-antineutrino pairs.U of I OnlyRestricted to the U of I community idenfinitely during batch ingest of legacy ETD