Tiny Tweaks, Different Fates: Exploring Supermassive Stellar Evolution with MESA

Direct-collapse black holes are potential sources of gravitational waves in the millihertz band and may originate from supermassive stars in the early universe. Using cosmological data from the Renaissance Simulations as input data to MESA, we model the evolution of supermassive stars through to collapse. The initial stellar conditions such as mass, angular momentum, and accretion rate, are drawn from the simulation outputs to ensure physical consistency with early universe environments. We explore how variations in the nuclear reaction network can alter the evolutionary tracks and pre-collapse structures of supermassive stars, presenting results that highlight the impact of the nuclear reaction network on the evolution and collapse pathways of these supermassive stars. These findings provide a foundation for future general-relativistic simulations of direct-collapse black hole formation, their gravitational wave signatures, and the potential for observation with space-based detectors.