Dynamical formation of the GW190814 merger

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 ${\Gamma }_{GW190814}\simeq 1-6$ yr Gpc${}^{-3}$, i.e. within the observational constraints set by the GW190814 discovery, ${\Gamma }_{\mathrm{LVC}}\sim 1-23$ 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.

main paper 7 pages, appendix 11 pages, 7 figures, 5 tables. Accepted for publication in ApJL

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