The First Stars

TL;DR

This review summarizes current knowledge on the formation of the first stars in the universe, focusing on physical processes, halo mass scales, and the potential for gas fragmentation affecting stellar masses.

Contribution

It provides a comprehensive overview of the physical mechanisms and current understanding of Population III star formation, highlighting areas needing further research.

Findings

Identification of dark matter halo mass scales for Population III stars

Analysis of gravitational collapse and protostellar density evolution

Discussion of gas fragmentation and its impact on stellar mass distribution

Abstract

The first stars to form in the Universe -- the so-called Population III stars -- bring an end to the cosmological Dark Ages, and exert an important influence on the formation of subsequent generations of stars and on the assembly of the first galaxies. Developing an understanding of how and when the first Population III stars formed and what their properties were is an important goal of modern astrophysical research. In this review, I discuss our current understanding of the physical processes involved in the formation of Population III stars. I show how we can identify the mass scale of the first dark matter halos to host Population III star formation, and discuss how gas undergoes gravitational collapse within these halos, eventually reaching protostellar densities. I highlight some of the most important physical processes occurring during this collapse, and indicate the areas where our current understanding remains incomplete. Finally, I discuss in some detail the behaviour of the gas after the formation of the first Population III protostar. I discuss both the conventional picture, where the gas does not undergo further fragmentation and the final stellar mass is set by the interplay between protostellar accretion and protostellar feedback, and also the recently advanced picture in which the gas does fragment and where dynamical interactions between fragments have an important influence on the final distribution of stellar masses.