Quasiequilibrium black hole-neutron star binaries in general relativity

TL;DR

This paper constructs and analyzes quasiequilibrium sequences of black hole-neutron star binaries in general relativity, providing numerical results on their properties, stability, and gravitational wave emission, improving understanding of such systems.

Contribution

It introduces a new method for modeling black hole-neutron star binaries without assuming extreme mass ratios or a curved background, extending previous work.

Findings

Excellent agreement with third-order post-Newtonian results at large separations.

Identified the onset of tidal disruption and innermost stable circular orbit.

Estimated gravitational wave energy spectrum during inspiral.

Abstract

We construct quasiequilibrium sequences of black hole-neutron star binaries in general relativity. We solve Einstein's constraint equations in the conformal thin-sandwich formalism, subject to black hole boundary conditions imposed on the surface of an excised sphere, together with the relativistic equations of hydrostatic equilibrium. In contrast to our previous calculations we adopt a flat spatial background geometry and do not assume extreme mass ratios. We adopt a Gamma=2 polytropic equation of state and focus on irrotational neutron star configurations as well as approximately nonspinning black holes. We present numerical results for ratios of the black hole's irreducible mass to the neutron star's ADM mass in isolation of M_{irr}^{BH}/M_{ADM,0}^{NS} = 1, 2, 3, 5, and 10. We consider neutron stars of baryon rest mass M_B^{NS}/M_B^{max} = 83% and 56%, where M_B^{max} is the maximum allowed rest mass of a spherical star in isolation for our equation of state. For these sequences, we locate the onset of tidal disruption and, in cases with sufficiently large mass ratios and neutron star compactions, the innermost stable circular orbit. We compare with previous results for black hole-neutron star binaries and find excellent agreement with third-order post-Newtonian results, especially for large binary separations. We also use our results to estimate the energy spectrum of the outgoing gravitational radiation emitted during the inspiral phase for these binaries.