MOCCA-SURVEY Database I: Eccentric Black Hole Mergers During Binary-Single Interactions In Globular Clusters

TL;DR

This study estimates the rate of eccentric black hole mergers during binary-single interactions in globular clusters, revealing a significantly higher occurrence than previous Newtonian models and providing an analytical framework for such events.

Contribution

It introduces the first analytical model to accurately estimate eccentric GW mergers during three-body interactions in realistic globular clusters.

Findings

Approximately 10% of BBH mergers form during chaotic interactions.

About half of these mergers have eccentricity > 0.1 at 10 Hz.

Eccentric merger rates are ~100 times higher than Newtonian predictions.

Abstract

We estimate the population of eccentric gravitational wave (GW) binary black hole (BBH) mergers forming during binary-single interactions in globular clusters (GCs), using ~ 800 GC models that were evolved using the MOCCA code for star cluster simulations as part of the MOCCA-Survey Database I project. By re-simulating binary-single interactions (only involving 3 BHs) extracted from this set of GC models using an N-body code that includes GW emission at the 2.5 post-Newtonian level, we find that ~ 10% of all the BBHs assembled in our GC models that merge at present time form during chaotic binary-single interactions, and that about half of this sample have an eccentricity > 0.1 at 10 Hz. We explicitly show that this derived rate of eccentric mergers is ~ 100 times higher than one would find with a purely Newtonian N-body code. Furthermore, we demonstrate that the eccentric fraction can be accurately estimated using a simple analytical formalism when the interacting BHs are of similar mass; a result that serves as the first successful analytical description of eccentric GW mergers forming during three-body interactions in realistic GCs.