The formation of merging black holes with masses beyond 30 M⊙ at solar metallicity

Gravitational-wave astronomy has revealed a population of stellar-mass black holes more massive than observed previously by other means. The maximum mass of black holes formed in isolated binaries is determined by stellar winds, mixing processes and interactions between the binary components. We consider the impact that fully self-consistent, detailed stellar-structure and binary-evolution calculations have on the population synthesis of black-hole binaries at solar metallicity. We find a qualitatively different picture from previous studies employing rapid population-synthesis techniques. Merging binary black holes form with a non-negligible rate ( $$\sim 4\times 1{0}^{-7}\,{M}_{\odot }^{-1}$$ ) and their progenitor stars with initial masses ≳50 M⊙ do not expand to supergiant radii, thereby largely avoiding substantial dust-driven or luminous blue variable winds. The progenitor stars lose less mass in winds, which results in black holes as massive as ~30 M⊙, and approximately half avoid a mass-transfer episode before forming the first-born black hole. Binaries with initial periods of a few days, some of which may undergo Roche-lobe overflow mass transfer, result in mildly spinning first-born black holes, χBH1 ≲ 0.2, assuming efficient angular-momentum transport. Using the POSYDON population synthesis code, this study predicts the existence of massive, thirty-solar-mass black-hole binaries in Milky-Way-like galaxies, challenging previous theories.