1207.6304 (Francois Foucart)

Black Hole-Neutron Star Mergers: Disk Mass Predictions    [PDF]

Francois Foucart

Determining the final result of black hole-neutron star mergers, and in particular the amount of matter remaining outside the black hole at late times, has been one of the main motivations behind the numerical simulation of these systems. Black hole-neutron star binaries are amongst the most likely progenitors of short gamma-ray bursts --- as long as they result in the formation of massive (at least ~0.1 solar mass) accretion disks around the black hole. Whether this actually happens strongly depends on the physical characteristics of the system, and in particular on the mass ratio, the spin of the black hole, and the radius of the neutron star. We present here a simple two-parameter model, fitted to existing numerical results, for the determination of the mass remaining outside the black hole a few milliseconds after a black hole-neutron star merger. This model predicts the remnant mass within a few percents of the mass of the neutron star, at least for remnant masses up to 20% of the neutron star mass. Results across the range of parameters deemed to be the most likely astrophysically are presented here. We find that, for 10 solar mass black holes, massive disks are only possible for fairly large neutron stars (R>12km), or quasi-extremal black hole spins (a/M>0.9). We also use our model to discuss how the equation of state of the neutron star affects the final remnant, and the strong influence that this can have on the rate of short gamma-ray bursts produced by black hole-neutron star mergers.

View original: http://arxiv.org/abs/1207.6304