Large Merger Recoils and Spin Flips from Generic Black-Hole Binaries

We report the first results from evolutions of generic black-hole binaries, i.e. a binary containing unequal mass black holes with misaligned spins. Our configuration, which has a mass ratio of 2 : 1, consists of an initially non-spinning hole orbiting a larger, rapidly spinning hole (specific spin a/m = 0.885), with the spin direction oriented −45◦ with respect to the orbital plane. We track the inspiral and merger for ∼ 2 orbits and find that the remnant receives a substantial kick of 454 kms−1, more than twice as large as the maximum kick from non-spinning binaries. The remnant spin direction is flipped by 103◦ with respect to the initial spin direction of the larger hole. We performed a second run with anti-aligned spins, a/m = ±0.5 lying in the orbital plane that produces a kick of ∼ 1830 kms−1 off the orbital plane. This value scales to nearly 4000 kms−1 for maximally spinning holes. Such a large recoil velocity opens the possibility that a merged binary can be ejected even from the nucleus of a massive host galaxy