Massive Black Hole formation in proto-stellar clusters via early gas accretion

Abstract

We review our semi-analytic model of stellar black hole (BH) mass growth by gas accretion in gas-rich stellar clusters during their birthstage within the first $\sim 10\,{\rm Myr}$ after the first stellar formation event. Such proto-stellar clusters are massive and compact, with typical masses $\sim 10^6\,{\rm M}_\odot$ and sizes $\sim 1\,{\rm pc}$, suggested by recent James Webb Space Telescope (JWST) observations. We find that the BH masses are shifted by the end of gas depletion 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 $\sim 10^3\,{\rm M}_\odot$.

Figures (3)

• Figure 1: Depletion timescale, $\tau$, with respect to the compactness, $C$, of a gas-rich stellar cluster of any total mass at low metallicity for different possible star formation efficiencies, $\varepsilon$.
• Figure 2: The sample maximum shifted individual BH mass in a stellar cluster with total stellar mass $M_\star = 10^6 {\rm M}_\odot$ and size $r_{{\rm c},\star} = 1{\rm pc}$, values representative of the observed Cosmic Gems proto-stellar clusters. The $x$-axis is the final, after gas depletion, stellar Plummer radius, to be compared to the half-light radius of the observed stellar clusters.
• Figure 3: Mass scatter diagram (a), and BH mass function (b), for a cluster with total stellar mass $M_\star = 10^6\,{\rm M}_\odot$ and final size $r_{{\rm c},\star} = 1\,{\rm pc}$, representing the observed Cosmic Gems proto-stellar clusters. In (a) the data refers to a single typical simulation. In (b) we use ten samples. The parameter $\alpha$ denotes the exponent of each histogram fit.