Mass growth of the first stars under radiative feedback

Abstract

We perform 3-D cosmological simulations to examine the growth of metal-free, Population III (Pop III) stars under radiative feedback. We trace the evolution of gas and dark matter until the formation of the first minihalo, and follow the collapse of the minihalo’s gas up to densities of n = 1012cm−3. We then implement the sink particle method while modeling the effect of Lyman-Werner (LW) and ionizing radiation emitted by the initial protostar over the next 5000 yr. A disk assembles around the first protostar, and radiative feedback does not prevent further fragmentation of the disk to form multiple Pop III stars. Feedback leads to heating of the dense gas to several thousand Kelvin, and this warm region expands outward at the gas sound speed. Once this region extends to the size of the disk, the disk mass declines while the accretion rate onto the protostars is reduced by an order of magnitude. The main sink will approach an asymptotic value of 30 M⊙ by the time it reaches the main sequence. Such unexpectedly low Pop III masses may have important consequences for the occurrence of pair-instability supernovae in the early Universe as well as the Pop III chemical signature in the oldest stars observable today.