Book chapter to appear in "The First Galaxies - Theoretical Predictions and Observational Clues", 2012 by Springer, eds. V. Bromm, B. Mobasher, T. Wiklind
astro-ph/1209.2509

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THE FIRST STARS

Simon C. O. Glover


Universität Heidelberg, Zentrum für Astronomie, Institut für Theoretische Astrophysik, Albert-Ueberle-Str. 2, 69120 Heidelberg

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.


Table of Contents

FORMATION OF THE FIRST STAR-FORMING MINIHALO
The Jeans mass and the filter mass
Cooling and chemistry in primordial gas
The minimum mass scale for collapse

GRAVITATIONAL COLLAPSE AND THE FORMATION OF THE FIRST PROTOSTAR
Thermal and chemical evolution of the gas during collapse
Dark matter annihilation
The role of magnetic fields

EVOLUTION AFTER THE FORMATION OF THE FIRST PROTOSTAR
The smooth accretion model
The fragmentation model

SUMMARY

REFERENCES

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