Dynamical formation of the GW190814 merger

TL;DR

This study models the dynamical formation of GW190814-like mergers in dense star clusters, finding that such events are likely in young, metal-rich environments and can explain observed merger rates and characteristics.

Contribution

It introduces a large-scale N-body simulation database to explore the dynamical origins of GW190814-like mergers, highlighting the role of specific cluster environments and remnant mass distributions.

Findings

GW190814-like mergers are likely formed in young, metal-rich clusters.

The model predicts detection rates consistent with GW190814 observations.

A small excess of 2.3-3 M$_\

Abstract

We investigate the possible dynamical origin of GW190814, a gravitational wave (GW) source discovered by the LIGO-Virgo-Kagra collaboration (LVC) associated with a merger between a stellar black hole (BH) with mass $23.2$ M$_\odot$ and a compact object, either a BH or a neutron star (NS), with mass $2.59$ M$_\odot$. Using a database of 240,000 $N$-body simulations modelling the formation of NS-BH mergers via dynamical encounters in dense clusters, we find that systems like GW190814 are likely to form in young, metal-rich clusters. Our model suggests that a little excess ($\sim 2-4\%$) of objects with masses in the range $2.3-3$ M$_\odot$ in the compact remnants mass spectrum leads to a detection rate for dynamically formed "GW190814 -like" mergers of $\Gamma_{\rm GW190814} \simeq 1-6$ yr Gpc$^{-3}$, i.e. within the observational constraints set by the GW190814 discovery, $\Gamma_{\rm LVC} \sim 1-23$ yr Gpc$^{-3}$. Additionally, our model suggests that $\sim 1.8-4.8\%$ of dynamical NS-BH mergers are compatible with GW190426\_152155, the only confirmed NS-BH merger detected by the LVC. We show that the relative amount of light and heavy NS-BH mergers can provide clues about the environments in which they developed.