A semi-relativistic model for tidal interactions in BH–NS coalescing binaries

We study the tidal effects of a Kerr black hole on a neutron star in black hole–neutron star (BH–NS) binary systems by using a semi-analytical approach which describes the neutron star as a deformable ellipsoid. Relativistic effects on the neutron star self-gravity are taken into account by employing a scalar potential resulting from relativistic stellar structure equations. We calculate quasi-equilibrium sequences of BH–NS binaries and the critical orbital separation at which the star is disrupted by the black hole tidal field: the latter quantity is of particular interest because when it is greater than the radius of the innermost stable circular orbit, a short gamma-ray burst scenario may develop.