Stellar Evolution at Low Metallicity

TL;DR

This review discusses how low metallicity affects massive star evolution, highlighting the roles of rotation, mass loss, and magnetic fields in producing key elements and phenomena like supernovae and gamma-ray bursts.

Contribution

It provides a comprehensive overview of the effects of metallicity, rotation, and magnetic fields on massive star evolution at very low metallicities, integrating recent modeling insights.

Findings

Rotation induces mixing, producing primary nitrogen, carbon, and neon.

Mass loss enables Wolf-Rayet star formation and supernova types at low Z.

Galactic chemical evolution models with rotation better match observed early universe element ratios.

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 review, we first recall the effect of metallicity (Z) on the evolution of massive stars. We then 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. Finally, the impact of magnetic fields is discussed in the context of GRBs.