Amplification of superkicks in black-hole binaries through orbital eccentricity

Abstract

We present new numerical-relativity simulations of eccentric merging black holes with initially anti-parallel spins lying in the orbital plane (the so-called 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