Gravitational recoil from spinning binary black hole mergers

TL;DR

This paper demonstrates that equal-mass spinning binary black hole mergers can produce significant gravitational recoil velocities, potentially ejecting the resulting black hole from dwarf galaxy cores.

Contribution

It presents new simulation results showing how spins in equal-mass binaries influence recoil velocities, extending previous studies focused on non-spinning cases.

Findings

Recoil velocity can reach 475 km/s for maximal spins.

Opposite spins aligned/anti-aligned with orbital angular momentum produce significant kicks.

Supermassive black hole mergers may eject black holes from dwarf galaxies.

Abstract

The inspiral and merger of binary black holes will likely involve black holes with both unequal masses and arbitrary spins. The gravitational radiation emitted by these binaries will carry angular as well as linear momentum. A net flux of emitted linear momentum implies that the black hole produced by the merger will experience a recoil or kick. Previous studies have focused on the recoil velocity from unequal mass, non-spinning binaries. We present results from simulations of equal mass but spinning black hole binaries and show how a significant gravitational recoil can also be obtained in these situations. We consider the case of black holes with opposite spins of magnitude $a$ aligned/anti-aligned with the orbital angular momentum, with $a$ the dimensionless spin parameters of the individual holes. For the initial setups under consideration, we find a recoil velocity of $V = 475 \KMS a$. Supermassive black hole mergers producing kicks of this magnitude could result in the ejection from the cores of dwarf galaxies of the final hole produced by the collision.