Merging black hole binaries: the effects of progenitor's metallicity, mass-loss rate and Eddington factor

Abstract

The first four gravitational wave events detected by LIGO were all interpreted as merging black hole binaries (BHBs), opening a new perspective on the study of such systems. Here we use our new population-synthesis code MOBSE, an upgraded version of BSE (Hurley et al. 2002), to investigate the demography of merging BHBs. MOBSE includes metallicity-dependent prescriptions for mass loss of massive hot stars. It also accounts for the impact of the electron-scattering Eddington factor on mass loss. We perform > 10 8 simulations of isolated massive binaries, with 12 different metallicities, to study the impact of mass loss, core-collapse supernovae and common envelope on merging BHBs. Accounting for the dependence of stellar winds on the Eddington factor leads to the formation of black holes (BHs) with mass up to 65 M at metallicity Z ∼ 0.0002. However, most BHs in merging BHBs have masses 40 M . We find merging BHBs with mass ratios in the 0.1−1.0 range, even if mass ratios > 0.6 are more likely. We predict that systems like GW150914, GW170814 and GW170104 can form only from progenitors with metallicity Z ≤ 0.006, Z ≤ 0.008 and Z ≤ 0.012, respectively. Most merging BHBs have gone through a common envelope phase, but up to ∼ 17 per cent merging BHBs at low metallicity did not undergo any common envelope phase. We find a much higher number of mergers from metal-poor progenitors than from metalrich ones: the number of BHB mergers per unit mass is ∼ 10 −4 M −1 at low metallicity (Z = 0.0002 − 0.002) and drops to ∼ 10 −7 M −1 at high metallicity (Z ∼ 0.02).

Highly spinning and aligned binary black hole merger in the Advanced LIGO first observing run

“…A number of formation channels for binary black hole mergers have previously been suggested in the literature, including isolated binaries of massive stars that evolve through a common envelope phase [22][23][24][25][26][27][28][29][30][31][32][33][34][35][36][37], or through a phase of chemically homogeneous evolution [38][39][40], few-body interactions at the core of dense stellar environments, such as old globular clusters [41][42][43][44][45][46][47][48][49], young open clusters [50][51][52][53], or nuclear clusters at the center of galaxies [54,55]. It has also been suggested that binaries are driven toward merger by nearby supermassive black holes [56], their accretion disks [57][58][59], or by tertiary stellar companions [60][61][62][63].…”

Gravitational-wave detection rates for compact binaries formed in isolation: LIGO/Virgo O3 and beyond

“…We use simulations performed with the populationsynthesis code MOBSE [16]. MOBSE is an upgrade of the arXiv:1906.04197v1 [gr-qc] 10 Jun 2019 Among the many physical processes involved in the formation of compact binaries that can merge within a Hubble time, the so called common-envelope phase is believed to be critical [19,20].…”

“…In Sec. II we present our astrophysical populations based on the MOBSE population-synthesis code [15,16]. In Sec.…”

Local merger rates of double neutron stars

“…A number of other groups published their results on DCO local merger rates during the last year. The highest NS-NS R loc of ∼600 Gpc −3 yr −1 quoted by Mapelli & Giacobbo (2018) (dashed green line in Fig. 1) was obtained assuming 5 times higher efficiency of CE ejection than in their reference model and additionally requiring that all NS form with low natal kicks (drawn from Maxwellian distribution with velocity dispersion σ=15 km/s).…”