Evolution of Very Massive Population III Stars with Mass Accretion from Pre-Main Sequence to Collapse

Abstract

We calculate the evolution of zero-metallicity Population III (Pop III) stars whose mass grows from the initial mass of $\sim 1M_{\odot}$ by accreting the surrounding gases. Our calculations cover a whole evolutionary stages from the pre-main sequence, via various nuclear burning stages, through the final core collapse or pair-creation instability phases. We adopt the following stellar mass-dependent accretion rates which are derived from cosmological simulations of early structure formation based on the low mass dark matter halos at redshifts $z \sim 20$: (1) the accretion rates for the first generation (Pop III.1) stars and (2) the rates for zero-metallicity but the second generation (Pop III.2) stars which are affected by radiation from the Pop III.1 stars. For comparison, we also study the evolution with the mass-dependent accretion rates which are affected by radiatibe feedback. We show that the final mass of Pop III.1 stars can be as large as $\sim 1000M_{\odot}$, beyond the mass range ($140 - 300M_{\odot}$) for the pair-instability supernovae. Such massive stars undergo core-collapse to form intermediate-mass black holes, which may be the seeds for merger trees to supermassive black holes. On the other hand, Pop III.2 stars become less massive ($\lsim 40 - 60M_{\odot}$), being in the mass range of ordinary iron core-collapse stars. Such stars explode and eject heavy elements to contribute to chemical enrichment of the early universe as observed in the abundance patterns of extremely metal-poor stars in the Galactic halo.