2026/01/12 by Antti Rantala, Thorsten Naab, Natalia Lahén +5
Physics and Astronomy · #Astrophysical Phenomena and Observations #Galaxies: Formation, Evolution, Phenomena #Astronomy and Astrophysical Research
paper · pdf · doi:10.1093/mnras/stag986
ABSTRACT We explore the formation of intermediate-mass black holes (IMBHs), potential seeds for supermassive black holes (SMBHs), via runaway stellar collisions for a wide range of star cluster (surface) densities (4× 103 \lesssim Σ h \lesssim 4× 106 \mathrmM_\odot pc-2) and metallicities (0.01 \lesssim Z \lesssim 1.0 Z_\odot ). Our sample of isolated (>1400) and hierarchical (30) simulations of young, massive star clusters with up to N=1.8× 106 stars includes collisional stellar dynamics, stellar evolution, and post-Newtonian equations of motion for black holes using the bifrost code. High stellar wind rates suppress IMBH formation at high metallicities (Z \gtrsim 0.2 Z_\odot ), and low collision rates prevent their formation at low densities (Σ h\lesssim 3× 104 \mathrmM_\odot pc-2). The assumptions about stellar wind loss rates strongly affect the maximum final IMBH masses (M_\bullet ∼ 6000 M_\odot versus M_\bullet ∼ 25 000 M_\odot ). The total stellar mass loss from collisions and collisionally boosted winds before t=3 Myr can together reach up to 5–10 per cent of the final cluster mass. We present fitting formulae for IMBH masses as a function of host star cluster Σ h and Z which can be used to seed SMBHs in high-resolution cosmological hydrodynamical simulations and in semi-analytic models for galaxy formation. Our results favour IMBH formation in dense low-metallicity environments similar to z∼ 10 JWST (James Webb Space Telescope) proto-globular clusters. IMBH formation is suppressed in the high-metallicity and low-density conditions of the local Universe.