GW190521 formation via three-body encounters in young massive star clusters. Issue 2 (1st October 2021)

• Record Type: Journal Article
• Authors: Dall'Amico, Marco; Mapelli, Michela; Di Carlo, Ugo N; Bouffanais, Yann; Rastello, Sara; Santoliquido, Filippo; Ballone, Alessandro; Arca Sedda, Manuel
• Is Part Of: Monthly notices of the Royal Astronomical Society. Volume 508:Issue 2(2021)
• Page Start: 3045
• Page End: 3054
• Publication Date: 2021-10-01
• Subjects: gravitational waves -- black hole physics -- methods: numerical -- stars: black holes -- stars: kinematics and dynamics -- galaxies: star clusters: general; Astronomy -- Periodicals; Periodicals; 520.5
• DOI: 10.1093/mnras/stab2783
• Languages: English
• ISSNs: 0035-8711

Abstract

ABSTRACT: GW190521 is the most massive binary black hole (BBH) merger observed to date, and its primary component lies in the pair-instability (PI) mass gap. Here, we investigate the formation of GW190521-like systems via three-body encounters in young massive star clusters. We performed 2 × 10 5 simulations of binary-single interactions between a BBH and a massive $\ge {60}\, $ M⊙ black hole (BH), including post-Newtonian terms up to the 2.5 order and a prescription for relativistic kicks. In our initial conditions, we take into account the possibility of forming BHs in the PI mass gap via stellar collisions. If we assume that first-generation BHs have low spins, $\sim {0.17}{{\ \rm per\ cent}}$ of all the simulated BBH mergers have component masses, effective and precessing spin, and remnant mass and spin inside the $90{{\ \rm per\ cent}}$ credible intervals of GW190521. Seven of these systems are first-generation exchanged binaries, while five are second-generation BBHs. We estimate a merger rate density $\mathcal {R}_{\rm GW190521}\sim {0.03}\, $ Gpc$^{-3}\, $ yr −1 for GW190521-like binaries formed via binary-single interactions in young star clusters. This rate is extremely sensitive to the spin distribution of first-generation BBHs. Stellar collisions, second-generation mergers and dynamical exchanges are the key ingredients to produce GW190521-like systems in young star clusters.