Dynamics of binary black holes in young star clusters: the impact of cluster mass and long-term evolution. Issue 2 (6th October 2022)

• Record Type: Journal Article
• Authors: Torniamenti, Stefano; Rastello, Sara; Mapelli, Michela; Di Carlo, Ugo N; Ballone, Alessandro; Pasquato, Mario
• Is Part Of: Monthly notices of the Royal Astronomical Society. Volume 517:Issue 2(2022)
• Page Start: 2953
• Page End: 2965
• Publication Date: 2022-10-06
• Subjects: black hole physics -- gravitational waves -- methods: numerical -- binaries: general -- stars: kinematics and dynamics -- galaxies: star clusters: general; Astronomy -- Periodicals; Periodicals; 520.5
• DOI: 10.1093/mnras/stac2841
• Languages: English
• ISSNs: 0035-8711

Abstract

ABSTRACT: Dynamical interactions in dense star clusters are considered one of the most effective formation channels of binary black holes (BBHs). Here, we present direct N -body simulations of two different star cluster families: low-mass (∼500–800 M⊙ ) and relatively high-mass star clusters (≥5000 M⊙ ). We show that the formation channels of BBHs in low- and high-mass star clusters are extremely different and lead to two completely distinct populations of BBH mergers. Low-mass clusters host mainly low-mass BBHs born from binary evolution, while BBHs in high-mass clusters are relatively massive (chirp mass up to ∼100 M⊙ ) and driven by dynamical exchanges. Tidal disruption dramatically quenches the formation and dynamical evolution of BBHs in low-mass clusters on a very short time-scale (≲100 Myr), while BBHs in high-mass clusters undergo effective dynamical hardening until the end of our simulations (1.5 Gyr). In high-mass clusters, we find that 8 per cent of BBHs have primary mass in the pair-instability mass gap at metallicity Z = 0.002, all of them born via stellar collisions, while only one BBH with primary mass in the mass gap forms in low-mass clusters. These differences are crucial for the interpretation of the formation channels of gravitational-wave sources.