Primordial massive supernovae as the first molecular factories in the early universe

Abstract

We study the ejecta chemistry of a zero-metallicity progenitor, massive, supernova using a novel approach based on chemical kinetics. Species considered span the range of simple, di-atomic molecules such as CO or SiO to more complex species involved in dust nucleation processes. We describe their formation from the gas phase including all possible relevant chemical processes and apply it to the ejecta of a primordial 170 Msun supernova. Two ejecta cases are explored: full mixing of the heavy elements, and a stratified ejecta reflecting the progenitor nucleosynthesis. Penetration of hydrogen from the progenitor envelope is considered. We show that molecules form very efficiently in the ejecta of primordial supernovae whatever the level of mixing and account for 13 to 34% of the total progenitor mass, equivalent to 21 to 57 Msun of the ejecta material in molecular form. The chemical nature of molecules depends on mixing of heavy elements and hydrogen in the ejecta. Species produced include O2, CO, CO2, SiS, SO, SiO and H2. Consequently, molecules can be used as observational tracers of supernova mixing after explosion. We conclude that primordial massive supernovae are the first molecule providers to the early universe.