Quasi-stars as a Means of Rapid Black Hole Growth in the Early Universe

TL;DR

This paper models the evolution of quasi-stars, suggesting they can produce supermassive black holes rapidly in the early universe, aligning with recent JWST observations of high-redshift SMBHs.

Contribution

It introduces new quasi-star models with an improved understanding of energy transport, extending the maximum black hole mass achievable during this phase to about 60% of the total quasi-star mass.

Findings

Maximum BH mass during quasi-star phase can reach ~60% of total mass.

Quasi-stars can form SMBHs within 20-40 million years.

Models are consistent with JWST observations of early SMBHs.

Abstract

JWST observations demonstrate that supermassive black holes (SMBHs) exist by redshifts $z \gtrsim 10$, providing further evidence for "direct collapse" black hole (BH) formation, whereby massive ($\sim 10^{3-5} M_{\odot}$) SMBH seeds are generated within a few Myr as a byproduct of the rapid inflow of gas into the centers of protogalaxies. Here we analyze the intermediate "quasi-star" phase that accompanies some direct collapse models, during which a natal BH accretes mass from and energetically sustains (through accretion) an overlying gaseous envelope. We argue that previous estimates of the maximum BH mass that can be reached during this stage, $\sim 1\%$ of the total quasi-star mass, are unphysical, and arise from underestimating the efficiency with which energy can be transported outward from regions close to the BH. We construct new quasi-star models that consist of an inner, "saturated-convection" region (which conforms to a convection-dominated accretion flow near the BH) matched to an outer, adiabatic envelope. These solutions exist up to a BH mass of $\sim 60\%$ the total quasi-star mass, at which point the adiabatic envelope contains only 2\% of the mass (with the remaining $\sim 38\%$ in the saturated-convection region), and this upper limit is reached within a time of $20-40$ Myr. We conclude that quasi-stars remain a viable route for producing SMBHs at large redshifts, consistent with recent JWST observations.