Speaker
Description
Intermediate-mass black holes (IMBHs), expected to lie in the ∼100-10000 solar mass range between stellar-mass and supermassive black holes, remain one of the least explored populations of compact objects. Gravitational-wave observations offer a promising way to characterize them by directly measuring black hole masses and spins. In this context, the recent candidate event GW231123 reported by the LIGO-Virgo-KAGRA (LVK) collaboration may provide the first evidence for a light IMBH binary.
In this talk, I investigate whether GW231123-like systems can naturally form in dense star clusters through repeated mergers of stars and binary black holes. To address this question, I analyze a suite of 3×3 simulations comprising 10⁷ binary black holes evolving in star clusters, performed with the population synthesis code B-POP. Our results indicate that stellar mergers in primordial binaries can significantly enhance the formation of GW231123-like systems in both young and globular clusters. However, the spins of merger remnant black holes play a crucial role in reproducing the properties inferred for the event. Finally, I estimate the intrinsic rate of GW231123-like mergers in dwarf and Milky Way-like galaxies and find it consistent with the estimate reported by the LVK collaboration.
Overall, these simulations provide insights into the dynamical contribution to the observed population of binary black hole mergers and help assess detection prospects for IMBHs with future third-generation gravitational-wave detectors such as the Einstein Telescope.