In this paper, we review our semi-analytic model of stellar black hole (BH) mass growth via gas accretion in gas-rich stellar clusters during their birthstage within the first ∼10Myr after the first stellar formation event. Such proto-stellar clusters are massive and compact, with typical masses ∼106M⊙ and sizes ∼1pc, as suggested by recent James Webb Space Telescope (JWST) observations. We find that by the end of the gas depletion process, BH masses are shifted to values within and above the BH mass gap, well within the range of components of the recent gravitational-wave (GW) signal GW231123, and up to masses ∼103M⊙.
Zacharias Roupas (2026) studied this question.