Accretion dynamics in neutron star-black hole binaries

We perform three-dimensional, Newtonian hydrodynamic simulations with a nuclear equation of state to investigate the accretion dynamics in neutron star–black hole systems. We find as a general result that non-spinning donor stars yield larger circularization radii than corotating donors. Therefore, the matter from a neutron star without spin will more likely settle into an accretion disc outside the Schwarzschild radius. With the stiff equation of state used we find it hard to form an accretion disc that is promising to launch a gamma-ray burst. In all relevant cases the core of the neutron star survives and keeps orbiting the black hole as a mini neutron star for the rest of the simulation time (up to several hundred dynamical neutron star time-scales). The existence of this mini neutron star leaves a clear imprint on the gravitational wave signal which thus can be used to probe the physics at supranuclear densities.