THE EARLY EVOLUTION OF PRIMORDIAL PAIR-INSTABILITY SUPERNOVAE

The observational signatures of the first cosmic explosions and their chemical imprint on second-generation stars both crucially depend on how heavy elements mix within the star at the earliest stages of the blast. We present numerical simulations of the early evolution of Population III (Pop III) pair-instability supernovae (PISNe) with the new adaptive mesh refinement code CASTRO. In stark contrast to 15-40 M-circle dot core-collapse primordial supernovae, we find no mixing in most 150-250 M-circle dot PISNe out to times well after breakout from the surface of the star. This may be the key to determining the mass of the progenitor of a primeval supernova, because vigorous mixing will cause emission lines from heavy metals such as Fe and Ni to appear much sooner in the light curves of core-collapse supernovae than in those of pair-instability explosions. Our models are consistent with observations of SN2007bi, the most likely PISN candidate found to date, which show that heavy elements in the interior of the SN are not mixed at all with helium in the outer envelope. Our results also imply that unlike low-mass Pop III supernovae, whose collective metal yields can be directly compared to the chemical abundances of extremely metal-poor stars, further detailed numerical simulations will be required to determine the nucleosynthetic imprint of very massive Pop III stars on their direct descendants.