Stellar Evolution in the Early Universe

TL;DR

This paper explores how rotation, mixing, and mass loss in massive stars at very low metallicity influence early universe evolution, primary element production, and chemical enrichment, with implications for understanding the first stars and galaxies.

Contribution

It introduces detailed models of rotating, low-metallicity massive stars showing their impact on element synthesis and early cosmic chemical evolution.

Findings

Enhanced primary nitrogen, carbon, and neon production due to mixing.

Mass loss leads to Wolf-Rayet stars and potential gamma-ray bursts at low Z.

Strong s-process element overproduction in massive stars.

Abstract

Massive stars played a key role in the early evolution of the Universe. They formed with the first halos and started the re-ionisation. It is therefore very important to understand their evolution. In this paper, we describe the strong impact of rotation induced mixing and mass loss at very low $Z$. The strong mixing leads to a significant production of primary nitrogen 14, carbon 13 and neon 22. Mass loss during the red supergiant stage allows the production of Wolf-Rayet stars, type Ib,c supernovae and possibly gamma-ray bursts (GRBs) down to almost Z=0 for stars more massive than 60 solar masses. Galactic chemical evolution models calculated with models of rotating stars better reproduce the early evolution of N/O, C/O and C12/C13. We calculated the weak s-process production induced by the primary neon 22 and obtain overproduction factors (relative to the initial composition, Z=1.e-6) between 100-1000 in the mass range 60-90.