Amplification of superkicks in black-hole binaries through orbital eccentricity

TL;DR

This paper demonstrates that orbital eccentricity in black-hole binaries significantly amplifies the recoil velocity of the merger remnant, mainly due to dynamic asymmetries, which could impact black hole retention in astrophysical environments.

Contribution

The study provides new numerical simulations showing how eccentricity enhances superkicks in black-hole mergers, a novel insight into black hole recoil mechanisms.

Findings

Eccentricity increases recoil velocity by up to 25%.

Energy flux increase is modest despite larger kicks.

Asymmetry in dynamics causes the kick enhancement.

Abstract

We present new numerical-relativity simulations of eccentric merging black holes with initially antiparallel spins lying in the orbital plane (the so-called \emph{superkick} configuration). Binary eccentricity boosts the recoil of the merger remnant by up to $25\%$. The increase in the energy flux is much more modest, and therefore this kick enhancement is mainly due to asymmetry in the binary dynamics. Our findings might have important consequences for the retention of stellar-mass black holes in star clusters and supermassive black holes in galactic hosts.