We have calculated the first dynamical evolutions of merging black hole-neutron star binaries that treat the combined spacetime in a nonperturbative general relativistic framework .
Using the conformal flatness approximation , we have studied how the location of the tidal disruption radius with respect to the the black hole horizon and innermost stable circular orbit ( ISCO ) affects the qualitative evolution of the system .
Based on simple arguments , we show that for a binary mass ratio q \mathrel { \hbox { \hbox to 0.0 pt { \hbox { \lower 4.0 pt \hbox { $ \sim$ } } } \hbox { $ > $ } } } 0.24 , tidal disruption occurs outside the ISCO , while the opposite is true for q \mathrel { \hbox { \hbox to 0.0 pt { \hbox { \lower 4.0 pt \hbox { $ \sim$ } } } \hbox { $ < $ } } } 0.24 .
When tidal disruption occurs sufficiently far outside the ISCO , mass is transferred unstably from the neutron star to the black hole , resulting in the complete disruption of the neutron star .
When tidal disruption occurs slightly within the ISCO , we find that some of the mass forms an extremely hot disk around the black hole .
The resulting configurations in this case are excellent candidates for the progenitors of short-hard gamma ray bursts .