All neutron stars obey a polytropic equation of state, P = Kρ0Γ, at t = 0. They are evolved according to the adiabatic evolution law, P = (Γ-1)ρ0&epsilon, where P is the pressure, K the polytropic constant, &epsilon is the internal specific energy, Γ is the adiabatic index, and ρ0 the rest-mass density. We chose Γ = 2 to mimick stiff nuclear matter. All stars are irrotational (nonspinning) and are in a quasiequilibrium circular orbit.
For spinning BHs we consider three different cases, all with mass ratio MBH:MNS = 3:1 : case A with ã = JBH/MBH2 =& nbsp;0, case B with ã = 0.75, and case C with ã = -0.50. For nonspinning BHs, we also consider three different mass ratios: case E with MBH:MNS = 1:1, case A with MBH:MNS = 3:1, and case D with MBH:MNS = 5:1.
The initial compaction of the neutron stars for all cases is MNS/RNS = 0.145. The rest mass is 83% of the maximum rest mass of an isolated, nonrotating NS with the same polytropic EOS.
The initial binary is in a quasiequilibrium circular orbit. The matter and gravitational field variables are determined by using the conformal thin-sandwich formalism. BH equilibrium boundary conditions are imposed on the BH horizon.