2026ApJ...998..150S

The origin of the first supermassive black holes (SMBHs) observed at redshifts z ≥ 9 remains one of the most challenging open questions in astrophysics. Their rapid emergence suggests that massive “heavy seeds” must have formed early, possibly through the direct collapse of pristine gas clouds in the first galaxies. We present Modules for Experiments in Stellar Astrophysics (MESA)-QUEST, a new framework built on the MESA code, designed to model the structure and evolution of quasi-stars-massive, radiation-supported envelopes hosting accreting black holes (BHs) at their cores-believed to be the progenitors of direct collapse BH seeds. Our implementation introduces flexible boundary conditions representing both Bondi accretion and saturated convection regimes and explores the impact of several stellar wind and mass-loss prescriptions, including Reimers, Dutch, and super-Eddington radiation-driven winds. We find that quasi-stars can grow central BHs to ≥10³M_⊙ under favorable conditions, with saturated convection models yielding black-hole-to-total mass ratios up to 0.55M_*-five times higher than Bondi-limited cases. However, strong radiation-driven winds can dramatically curtail growth, potentially quenching heavy-seed formation unless balanced by sustained envelope accretion. Our results delineate the physical limits under which quasi-stars can remain stable and produce heavy seeds capable of evolving into the earliest SMBHs detected by JWST and Chandra. Future extensions will incorporate rotation, magnetic fields, and general relativistic radiation hydrodynamics to refine accretion physics and constrain the viability of the quasi-star pathway for early SMBH formation.