General Relativistic Black Hole-Neutron Star Simulations: Effects of Black Hole Spin and Binary Mass Ratio
Etienne, Zachariah Burke
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https://hdl.handle.net/2142/80608
Description
Title
General Relativistic Black Hole-Neutron Star Simulations: Effects of Black Hole Spin and Binary Mass Ratio
Author(s)
Etienne, Zachariah Burke
Issue Date
2009
Doctoral Committee Chair(s)
Gammie, Charles F.
Department of Study
Physics
Discipline
Physics
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Physics, Astronomy and Astrophysics
Language
eng
Abstract
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⊙ ) 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 ≈ 0.2 M⊙ ), 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.
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