Modelling supermassive primordial stars with mesa

Abstract

ABSTRACT Supermassive stars forming at z ∼ 15–20 are one of the leading contenders for the origin of the first quasars, over 200 of which have now been discovered at z > 6. These stars likely form in pristine, atomically cooled haloes immersed in strong Lyman–Werner ultraviolet backgrounds or in highly supersonic baryon streaming flows. Atomic cooling triggers catastrophic baryon collapse capable of building up stars at rates of up to ∼1 M⊙ yr−1. Here, we examine the evolution of supermassive stars with a much larger and finer grid of accretion rates than in previous studies with the mesa stellar evolution code. We find that their final masses range from 3.5 × 103 to 3.7 × 105 M⊙ at accretion rates of 0.001–1 M⊙ yr−1, respectively. We also find that supermassive star evolution diverges at accretion rates of 0.01–0.02 M⊙ yr−1, above which they evolve as cool red hypergiants along the Hayashi track and collapse via the general relativistic instability during central hydrogen burning, and below which they evolve as hot blue supergiants and collapse at the end of their nuclear burning lifetimes after exiting the main sequence.