Merger rate density of Population III binary black holes below, above, and in the pair-instability mass gap

Abstract

We present the merger rate density of Population (Pop.) III binary black holes (BHs) by means of a widely-used binary population synthesis code BSE with extensions to very massive and extreme metalpoor stars. We consider not only low-mass BHs (lBHs: 5 − 50M ) but also high-mass BHs (hBHs: 130 − 200M ), where lBHs and hBHs are below and above the pair-instability mass gap (50 − 130M ), respectively. Pop. III BH-BHs can be categorized into three subpopulations: BH-BHs without hBHs (hBH0s: m tot 100M ), with one hBH (hBH1s: m tot ∼ 140 − 260M ), and with two hBHs (hBH2s:, where m tot is the total mass of a BH-BH. Their merger rate densities at the current universe are ∼ 0.1 yr −1 Gpc −3 for hBH0s, and ∼ 0.01 yr −1 Gpc −3 for the sum of hBH1s and hBH2s, using pessimistic Pop. III star formation model. These rates are modestly insensitive to initial conditions and single star models. The hBH1 and hBH2 mergers can dominate BH-BHs with hBHs discovered in near future. They have low effective spins 0.2 in the current universe. The number ratio of the hBH2s to the hBH1s is high, 0.1. We also find BHs in the mass gap (up to ∼ 85M ) merge. These merger rates can be reduced to nearly zero if Pop. III binaries are always wide ( 100R ), and if Pop. III stars always enter into chemically homogeneous evolution. The presence of close Pop. III binaries (∼ 10R ) are crucial for avoiding the worst scenario.

Hierarchical mergers of stellar-mass black holes and their gravitational-wave signatures

“…The pair-instability process immediately translates into a promising signature of hierarchical mergers in GW observations: if BHs with 50M m 120M cannot be produced by stars, they might well be the remnants of previous BH mergers. Possible caveats to this statement include envelope retention in low-metallicity population III stars, [52][53][54] stellar mergers prior to BH formation, 37,[55][56][57] evolution in detached binaries, 44 as well as accretion in either molecular clouds, 58 minihalos, 59 dense clusters, 60,61 or isolated binaries. 62…”

Host galaxies and electromagnetic counterparts to binary neutron star mergers across the cosmic time: Detectability of GW170817-like events

“…The evolution of stars in binary systems, and hence the properties of BNSs at the time of mergers, have been the subject of numerous investigations using population synthesis codes (e.g. Tutukov & Yun-gelson 1973;Portegies Zwart & Yungelson 1998;Belczynski et al 2002;Voss & Tauris 2003;Belczynski et al 2007;Podsiadlowski et al 2004;O'Shaughnessy et al 2010;Eldridge & Stanway 2016;Marchant et al 2016;Belczynski et al 2016;de Mink & Mandel 2016;Belczynski et al 2017;Stevenson et al 2017;Giacobbo et al 2018;Vigna-Gómez et al 2018;Neijssel et al 2019;Tang et al 2020;Tanikawa et al 2020;Mandel & Broekgaarden 2021), coupled with either semi-analytical prescriptions for galaxy modeling and evolution (e.g. Perna & Belczynski 2002;Belczynski et al 2006), or with results from numerical simulations of galaxy formation (e.g.…”

“…Events in galactic fields are more likely associated with compact object (CO) bina-ries formed via stellar evolution from binary stars (e.g. Tutukov & Yungelson 1973;Portegies Zwart & Yungelson 1998;Belczynski et al 2002;Voss & Tauris 2003;Belczynski et al 2007;Podsiadlowski et al 2004;Eldridge & Stanway 2016;Marchant et al 2016;Belczynski et al 2016;de Mink & Mandel 2016;Belczynski et al 2017;Stevenson et al 2017;Giacobbo et al 2018;Vigna-Gómez et al 2018;Belczynski et al 2018;Spera et al 2019;Tanikawa et al 2020), whereas mergers in globular clusters (e.g. Portegies Zwart & McMillan 2000;Downing et al 2010;Samsing et al 2014;Rodriguez et al 2015Rodriguez et al , 2016Askar et al 2017;Samsing 2018;Rodriguez & Loeb 2018;Fragione & Loeb 2019;Fragione et al 2019a,b;Zevin et al 2019;Fragione & Silk 2020;Antonini & Gieles 2020;Mapelli et al 2021), young star clusters (e.g.…”

Stellar winds and metal enrichment from fast-rotating Population III stars

“…Future studies should use more advanced stellar evolution grids that consider higher initial rotation speeds, additional mass loss processes, and a range of initial metallicities (Z 10 −4 Z ), together with close binary interactions (e.g. Kinugawa et al 2014;Belczynski et al 2017;Tanikawa et al 2020a). Furthermore, more realistic modelling of the feedback process has to involve 3D hydrodynamics (e.g.…”

“…Schauer et al 2019b;Qin et al 2020), and gravitational waves from mergers of compact objects (e.g. Kinugawa et al 2014;Hartwig et al 2016;Belczynski et al 2017;Tanikawa et al 2020a;Liu & Bromm 2020a,c).…”