Formation pathway of Population III coalescing binary black holes through stable mass transfer

Abstract

We study the formation of stellar mass binary black holes (BBHs) originating from Population III (PopIII) stars, performing stellar evolution simulations for PopIII binaries with MESA. We find that a significant fraction of PopIII binaries form massive BBHs through stable mass transfer between two stars in a binary, without experiencing common envelope phases. We investigate necessary conditions required for PopIII binaries to form coalescing BBHs with a semi-analytical model calibrated by the stellar evolution simulations. The BBH formation efficiency is estimated for two different initial conditions for PopIII binaries with large and small separations, respectively. Consequently, in both models, ∼ 10% of the total PopIII binaries form BBHs only through stable mass transfer and ∼ 10% of these BBHs merge due to gravitational wave emission within the Hubble time. Furthermore, the chirp mass of merging BBHs has a flat distribution over 15 < ∼ M chirp /M < ∼ 35. This formation pathway of PopIII BBHs is presumably robust because stable mass transfer is less uncertain than common envelope evolution, which is the main formation channel for Population II BBHs. We also test the hypothesis that the BBH mergers detected by LIGO originate from PopIII stars using the total number of PopIII stars formed in the early universe as inferred from the optical depth measured by Planck. We conclude that the PopIII BBH formation scenario can explain the mass-weighted merger rate of the LIGO's O1 events with the maximal PopIII formation efficiency inferred from the Planck measurement, even without BBHs formed by unstable mass transfer or common envelope phases.

GW170104: Observation of a 50-Solar-Mass Binary Black Hole Coalescence at Redshift 0.2

“…Isolated binary evolution in galactic fields classically proceeds via a common envelope [97][98][99][100][101][102][103][104][105]. Variants avoiding common-envelope evolution include (quasi-)chemically homogeneous evolution of massive tidally locked binaries [101,106,107], or through stable mass transfer in Population I [108,109] or Population III binaries [110,111].…”

Formation of the First Star Clusters and Massive Star Binaries by Fragmentation of Filamentary Primordial Gas Clouds

“…Our simulations show the formation of a hard binary of massive stars at the center of the star cluster. If the remnant BHs with dozens of solar masses form an eccentric close-binary system, it emits strong gravitational waves with a characteristic signatures at the final merger phase (Kinugawa et al 2014(Kinugawa et al , 2016Inayoshi et al 2017). In fact, mergers of massive BHs at the presentday Universe have been already detected (Abbott et al 2016), and the origin of the massive BHs could be the first stars.…”

Merger history of primordial black-hole binaries

“…The progenitors of these BBHs are still unknown and under intensively investigation (see e.g. [8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27]). These LIGO/Virgo BBHs present a much heavier mass distribution (in particular the sourceframe primary mass of GW170729 event can be as heavy as 50.2 +16.2 −10.2 M [7]) than that inferred from X-ray observations [28][29][30][31], which would challenge the formation and evolution mechanisms of astrophysical black holes.…”