Close Encounter of Three Black Holes Revisited

TL;DR

This study uses numerical relativity to analyze how a third black hole influences the merger dynamics of a close triple black hole system, revealing a distance-dependent delay and eccentricity modulation.

Contribution

It provides the first detailed numerical analysis of triple black hole interactions, highlighting the effects of a third black hole on binary merger time and eccentricity evolution.

Findings

Merger delay scales as ~1/D^{2.5} with distance D.

Orientation of the third black hole has minimal effect at D=30M.

Eccentricity decay shows modulation at the outer orbit's semiperiod.

Abstract

We study the evolution of close triple black hole system with full numerical relativity techniques. We consider an equal mass non spinning hierarchical system with an inner binary ten orbits away from merger and study the effects of the third outer black hole on the binary's merger time and its eccentricity evolution. We find a generic time delay and an increase in the number of orbits to merger of the binary, that can be modeled versus the distance $D$ to the third black hole as $\sim1/D^{2.5}$. On the other hand, we find that the orientation of the third black hole orbit has little effect on the binary's merger time when considering a fiducial initial distance of $D=30M$ to the binary (with initial orbital separation $d=8M$). In those scenarios the evolution of the inner binary eccentricity presents a steady decay, roughly as expected, but in addition shows a modulation with the time scale of the outer third black hole orbital semiperiod around the binary, resembling a beating frequency.