Unequal mass binary black hole plunges and gravitational recoil

We present results from fully nonlinear simulations of unequal mass binary black holes plunging from close separations well inside the innermost stable circular orbit with mass ratios q ≡ M1/M2 = {1, 0.85, 0.78, 0.55, 0.32}, or equivalently, with reduced mass parameters η ≡ M1M2/(M1 + M2)2 = {0.25, 0.248, 0.246, 0.229, 0.183}. For each case, the initial binary orbital parameters are chosen from the Cook–Baumgarte equal-mass ISCO configuration. We show waveforms of the dominant ℓ = 2, 3 modes and compute estimates of energy and angular momentum radiated. For the plunges from the close separations considered, we measure kick velocities from gravitational radiation recoil in the range 25–82 km s−1. Due to the initial close separations our kick velocity estimates should be understood as a lower bound. The close configurations considered are also likely to contain significant eccentricities influencing the recoil velocity.