The chemistry of population III supernova ejecta: II - The nucleation of molecular clusters as a diagnostic for dust in the early universe

TL;DR

This study models the formation of molecular precursors to dust in Population III supernova ejecta, revealing smaller dust yields and different compositions than previously thought, with implications for early universe dust enrichment.

Contribution

It introduces a new chemical reaction network for nucleation in supernova ejecta and highlights the impact of mixing and pressure on dust formation, correcting prior assumptions.

Findings

Unmixed ejecta of 170 Msun supernova produce ~5.6 Msun of small clusters.

Unmixed ejecta of 20 Msun supernova produce ~0.103 Msun of small clusters.

Dust yields are about five times lower than previous estimates, with different compositions.

Abstract

We study the formation of molecular precursors to dust in the ejecta of Population III supernovae using a chemical kinetic approach. Our work focuses on zero-metallicity 20 Msun and 170 Msun progenitors, and we consider fully-macroscopically mixed and unmixed ejecta. The nucleation stage for small silica, metal oxides and sulphides, pure metal, and carbon clusters is described with a new chemical reaction network. We consider the effect of the pressure dependence of critical nucleation rates, and test the impact of microscopically-mixed He+ on carbon dust formation. The unmixed ejecta of a 170 Msun progenitor supernova synthesizes ~ 5.6 Msun of small clusters, while its 20 Msun counterpart produces ~ 0.103 Msun. Our results point to smaller amounts of dust formed in the ejecta of Pop. III supernovae by a factor ~ 5 compared to values derived by previous studies, and to different dust chemical composition. Such deviations result from some erroneous assumptions made, the inappropriate use of classical nucleation theory to model dust formation, and the omission of the synthethis of molecules in supernova ejecta. Unmixed ejecta of massive Pop. III supernovae chiefly form silica and/or silicates, and pure silicon grains whereas their lower mass counterparts form a dust mixture dominated by silica and/or silicates, pure silicon and iron sulphides. Amorphous carbon can only condense in ejecta where the carbon-rich zone is deprived of He+. The first dust enrichment to the primordial gas in the early universe from Pop. III massive supernova comprises primarily pure silicon, silica and silicates. If carbon dust is present at redshift z> 6, alternative dust sources must be considered.