From Darkness to Light: The First Stars in the Universe

Abstract.

Paramount among the processes that ended the cosmic ‘dark ages’ must have been the formation of the first generation of stars. In order to constrain its nature, we investigate the collapse and fragmentation of metal-free gas clouds. We explore the physics of primordial star formation by means of three-dimensional simulations of the dark matter and gas components, using smoothed particle hydrodynarnics. We find characteristic values for the temperature, $T \sim$ a few 100 K, and the density, $n \sim 10^3 - 10^4$ cm^-3, characterising the gas at the end of the initial free-fall phase. The corresponding Jeans mass is $M_J \sim 10^3 M_\odot$. The existence of these characteristic values has a robust explanation in the microphysics of H₂ cooling, and is not very sensitive to the cosmological initial conditions. These results suggest that the first stars might have been quite massive, possibly even very massive with $M_* > 100M_\odot$.