Dynamical Formation of the GW190814 Merger

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⊙ and a compact object, either a BH or a neutron star (NS), with mass 2.59 M⊙. Using a database of 240,000 N-body simulations modeling 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 (∼2%–4%) of objects with masses in the range of 2.3–3 M⊙ in the compact remnants' mass spectrum leads to a detection rate for dynamically formed "GW190814 -like" mergers of ΓGW190814 ≃ 1–6 yr−1 Gpc−3, i.e., within the observational constraints set by the GW190814 discovery, ΓLVC ∼ 1–23 yr−1 Gpc−3. Additionally, our model suggests that ∼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.