Spinning-black-hole binaries: The orbital hang up

TL;DR

This study uses fully nonlinear numerical simulations to explore how the spins of black holes in binaries influence their orbital dynamics and merger outcomes, revealing significant effects on the number of orbits before merging and the spin of the remnant.

Contribution

First fully nonlinear numerical analysis of highly spinning black-hole binaries, demonstrating the impact of spin orientation on merger dynamics and remnant properties.

Findings

Aligned spins lead to more orbits before merger (~3)

Anti-aligned spins result in fewer orbits (<1)

Energy radiated varies with spin alignment (~7% vs ~2%)

Abstract

We present the first fully-nonlinear numerical study of the dynamics of highly spinning black-hole binaries. We evolve binaries from quasicircular orbits (as inferred from Post-Newtonian theory), and find that the last stages of the orbital motion of black-hole binaries are profoundly affected by their individual spins. In order to cleanly display its effects, we consider two equal mass holes with individual spin parameters S/m^2=0.757, both aligned and anti-aligned with the orbital angular momentum (and compare with the spinless case), and with an initial orbital period of 125M. We find that the aligned case completes three orbits and merges significantly after the anti-aligned case, which completes less than one orbit. The total energy radiated for the former case is ~7% while for the latter it is only ~2%. The final Kerr hole remnants have rotation parameters a/M=0.89 and a/M=0.44 respectively, showing the unlikeliness of creating a maximally rotating black hole out of the merger of two spinning holes.