Superkicks in Hyperbolic Encounters of Binary Black Holes

TL;DR

This paper investigates gravitational recoil in hyperbolic binary black hole encounters, revealing that such interactions can produce significantly larger kick velocities than previously observed in quasi-circular inspirals.

Contribution

It is the first study to analyze gravitational recoil in hyperbolic black hole encounters, highlighting the potential for much higher kick velocities due to plunge-dominated radiation.

Findings

Hyperbolic encounters can produce kicks up to 10,000 km/s.

Radiation from hyperbolic encounters is plunge dominated, enhancing beaming.

Compared to quasi-circular inspirals, hyperbolic encounters lead to larger recoil velocities.

Abstract

Generic inspirals and mergers of binary black holes produce beamed emission of gravitational radiation that can lead to a gravitational recoil or kick of the final black hole. The kick velocity depends on the mass ratio and spins of the binary as well as on the dynamics of the binary configuration. Studies have focused so far on the most astrophysically relevant configuration of quasi-circular inspirals, for which kicks as large as 3,300 km/s have been found. We present the first study of gravitational recoil in hyperbolic encounters. Contrary to quasi-circular configurations, in which the beamed radiation tends to average during the inspiral, radiation from hyperbolic encounters is plunge dominated, resulting in an enhancement of preferential beaming. As a consequence, it is possible to achieve kick velocities as large as 10,000 km/s.