Quasiequilibrium sequences of black hole-neutron star binaries in general relativity
05/02/2008 - 11:30am to 12:30pm
In this talk, I will describe our recent progress on quasiequilibrium black hole-neutron star binaries in general relativity. In our model, we solve Einstein's constraint equations in the conformal thin-sandwich decomposition together with the relativistic equations of hydrostationary equilibrium. We adopt maximal slicing, assume spatial conformal flatness, and impose equilibrium boundary conditions on an excision surface (apparent horizon) to model the black hole. In our previous treatments we adopted a ``leading-order" approximation for a parameter related to the black-hole spin in these horizon boundary conditions to construct approximately nonspinning black holes. Here we improve on the models by computing the black hole's quasilocal spin angular momentum and setting it to zero. As before, we adopt a polytropic equation of state with adiabatic index $\Gamma=2$ and assume the neutron star to be irrotational. We show results for a wide range of neutron star masses and binary mass ratios, identifying the location of the innermost stable circular orbit and the onset of the tidal disruption. Finally, we show very recent results of spinning black hole-neutron star binaries in quasiequilibrium circular orbit, and discuss how the spin of the black hole affects the location of the innermost stable circular orbit and the onset of the tidal disruption.
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