Modelling supermassive primordial stars with mesa

Supermassive stars forming at z similar to 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 similar to 1 M-circle dot 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 x 10(3) to 3.7 x 10(5) M-circle dot at accretion rates of 0.001-1 M-circle dot yr(-1), respectively. We also find that supermassive star evolution diverges at accretion rates of 0.01-0.02 M-circle dot 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.