Hydrodynamics of black hole-neutron star coalescence

We present a numerical study of the hydrodynamics in the final stages of inspiral in a black hole-neutron star binary, when the separation becomes comparable to the stellar radius. We use a Newtonian 3D Smooth Particle Hydrodynamics (SPH) code and model the neutron star with a stiff equation of state. The black hole is modeled as a point mass with an absorbing boundary at the Schwarzschild radius. The initial conditions correspond to irrotational binaries in equilibrium, and we follow the evolution of the system for approximately 23 ms. We find that the result of the initial interaction between the stars is an intense episode of mass transfer, and the details of the subsequent evolution depend greatly on the assumed stiffness of the equation of state. We find that an accretion disk containing a few tenths of a solar mass is formed around the black hole, and that up to 0.1 solar masses of material may be dynamically ejected from the system. Our results show that these systems are promising candidates for the production of short gamma ray bursts.