Close Encounter of Three Black Holes III

TL;DR

This paper uses numerical relativity to study hierarchical three-black-hole systems, revealing how spin and orbital configurations affect merger times and interactions, with implications for understanding complex black hole dynamics.

Contribution

It introduces new insights into the delay of binary mergers due to spin-orbit coupling and explores mass ratio effects in triple black hole systems.

Findings

Merger delay scales as ~1/D^{1.6} for spinning black holes.

Spin-orbit coupling significantly influences merger timing.

Higher mass ratios and counter-orbiting configurations increase merger times.

Abstract

We revisit the three black hole scenario with numerical relativity techniques to study hierarchical configurations where the inner binary contains highly spinning black holes. We find that the merger time of the binary gets a delay (with a number of orbits to merger increase), depending strongly with the distance to the orbiting third hole $D$ as $\sim1/D^{1.6\pm0.1}$. Notably, a different dependence from what we had found in the nonspinning case, $\sim1/D^{2.5}$. We interpret this effect as mostly due to a spin-orbit coupling between the third hole and the closest member of the binary in the successive approaches. This lead us next to study scattering configurations of the third hole with the binary in order to evaluate the extent of this ``sudden'' interactions, finding also a correlation of the delay in merger times with the closest distance, even for the nonspinning cases. We then explore the mass ratio dependence of the triple system by modeling binaries orbiting a larger black hole bearing masses ratios 8:1:1 and 18:1:1 in co-orbiting or counter-orbiting configurations, finding merger times increasing with increasing mass ratios and for the counter-orbiting cases.