Fates of the most massive primordial stars

We present our results of numerical simulations of the most massive primordial stars. For the extremely massive non-rotating Pop III stars over 300M_⊙, they would simply die as black holes. But the Pop III stars with initial masses 140 - 260M_⊙ may have died as gigantic explosions called pair-instability supernovae (PSNe). We use a new radiation-hydrodynamics code CASTRO to study evolution of PSNe. Our models follow the entire explosive burning and the explosion until the shock breaks out from the stellar surface. In our simulations, we find that fluid instabilities occurred during the explosion. These instabilities are driven by both nuclear burning and hydrodynamical instability. In the red supergiant models, fluid instabilities can lead to significant mixing of supernova ejecta and alter the observational signature.