2023/08/21 by Debatri Chattopadhyay, Chattopadhyay, Debatri, Jakob Stegmann +7 · 12 citations
Physics and Astronomy · #Astrophysical Phenomena and Observations #Astrophysics of Galaxies (astro-ph.GA) #FOS: Physical sciences #Gamma-ray bursts and supernovae #General Relativity and Quantum Cosmology (gr-qc) #High Energy Astrophysical Phenomena (astro-ph.HE) #Pulsars and Gravitational Waves Research
paper · pdf · doi:10.48550/arxiv.2308.10884
openalex publication_date 2023/08/21 · openalex created_date 2023/08/23 · openalex updated_date 2026/07/28
We investigate the formation of intermediate mass black holes (IMBHs) through hierarchical mergers of stellar origin black holes (BHs), as well as BH mergers formed dynamically in nuclear star clusters. Using a semi-analytical approach which incorporates probabilistic mass-function-dependent double BH (DBH) pairing, binary-single encounters, and a mass-ratio-dependent prescription for energy dissipation in hardening binaries, we find that IMBHs with masses of O(102)-O(104)\rm M_\odot can be formed solely through hierarchical mergers in timescales of a few 100 Myrs to a few Gyrs. Clusters with escape velocities \gtrsim400 km s-1 inevitably form high-mass IMBHs. The spin distribution of IMBHs with masses \gtrsim 103 M_\odot is strongly clustered at χ∼ 0.15; while for lower masses, it peaks at χ∼ 0.7. Eccentric mergers are more frequent for equal-mass binaries containing first-and/or second-generation BHs. Metal-rich, young, dense clusters can produce up to 20% of their DBH mergers with eccentricity ≥0.1 at 10 \rm Hz, and ∼2-9% of all in-cluster mergers can form at >10 Hz. Nuclear star clusters are therefore promising environments for the formation of highly-eccentric DBH mergers, detectable with current gravitational-wave detectors. Clusters of extreme mass (∼108 M_\odot) and density (∼108 M_\odotpc-3) can have about half of all of their DBH mergers with primary masses ≥100 M_\odot. The fraction of in-cluster mergers increases rapidly with increasing cluster escape velocity, being nearly unity for v\rm esc\gtrsim 200 km s-1. Cosmological merger rate of DBHs from nuclear clusters varies \lessapprox0.01-1 Gpc-3yr-1.