Orbiting black-hole binaries and apparent horizons in higher dimensions

TL;DR

This paper investigates gravitational waves and apparent horizons in higher-dimensional black-hole binaries, introducing a new horizon finder and analyzing their dynamics and radiation in six dimensions.

Contribution

It presents a novel apparent horizon finder for higher-dimensional simulations and studies the dynamics and gravitational wave emission of black-hole binaries in six dimensions.

Findings

Binaries complete about one orbit before merging or scattering.

Binaries radiate 0.13% to 0.2% of total mass-energy in gravitational waves.

No stable circular orbits or multiple orbits without fine-tuning were observed.

Abstract

We study gravitational wave emission and the structure and formation of apparent horizons in orbiting black-hole binary systems in higher-dimensional general relativity. For this purpose we present an apparent horizon finder for use in higher dimensional numerical simulations and test the finder's accuracy and consistency in single and binary black-hole spacetimes. The black-hole binaries we model in $D=6$ dimensions complete up to about one orbit before merging or scatter off each other without formation of a common horizon. In agreement with the absence of stable circular geodesic orbits around higher-dimensional black holes, we do not find binaries completing multiple orbits without finetuning of the initial data. All binaries radiate about $0.13\,\%$ to $0.2\,\%$ of the total mass-energy in gravitational waves, over an order of magnitude below the radiated energy measured for four-dimensional binaries. The low radiative efficiency is accompanied by relatively slow dynamics of the binaries as expected from the more rapid falloff of the binding gravitational force in higher dimensions.