We use a 3-D relativistic SPH ( Smoothed Particle Hydrodynamics ) code to study mergers of black hole – neutron star ( BH–NS ) binary systems with low mass ratios , adopting q \equiv M _ { NS } / M _ { BH } \simeq 0.1 as a representative case .
The outcome of such mergers depends sensitively on both the magnitude of the BH spin and its obliquity ( i.e. , the inclination of the binary orbit with respect to the equatorial plane of the BH ) .
In particular , only systems with sufficiently high BH spin parameter a and sufficiently low orbital inclinations allow any NS matter to escape or to form a long-lived disk outside the BH horizon after disruption .
Mergers of binaries with orbital inclinations above \sim 60 ^ { o } lead to complete prompt accretion of the entire NS by the BH , even for the case of an extreme Kerr BH .
We find that the formation of a significant disk or torus of NS material around the BH always requires a near-maximal BH spin and a low initial inclination of the NS orbit just prior to merger .