paper

Newtonian hydrodynamics of the coalescence of black holes with neutron stars III: Irrotational binaries with a stiff equation of state

arXiv:astro-ph/0007206 · doi:10.1046/j.1365-8711.2000.03870.x

Abstract

We present a hydrodynamical study of the final stages of inspiral in a black hole-neutron star (NS) binary. We use a Newtonian 3D SPH code, and model the NS with a stiff (index G=3 and G=2.5) polytropic equation of state and the black hole as a Newtonian point mass. Our initial conditions correspond to irrotational binaries in equilibrium (approximating the NS as a compressible ellipsoid), and we have explored configurations with different initial mass ratios, 0.2< q=M_ns/M_bh<0.5. The dynamical evolution is followed for ~23ms. We include gravitational radiation losses in the quadrupole approximation for a point-mass binary. For G=3, after an initial episode of mass transfer, the NS is not completely disrupted and a remnant core remains in orbit about the black hole. For G=2.5 the disruption is more complex, with the NS being totally disrupted during a second periastron passage. The accretion disc formed around the black hole contains ~0.2 solar masses. A nearly baryon-free axis is always present in the system, and only modest beaming of a relativistic fireball that could give rise to a GRB would be sufficient to avoid baryon contamination. Around 0.01 solar masses may be dynamically ejected from the system, and could contribute substantially to the amount of observed galactic r-process material. We calculate the gravitational radiation waveforms in the quadrupole approximation. We also present the results of simulations that have used spherical NSs relaxed in isolation as initial conditions, in order to gauge the effect of using non-equilibrium initial conditions on the coalescence.

Accepted for publication in MNRAS, 23 pages, 15 figures

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