First star formation with dark matter annihilation

Abstract

We include an energy term based on dark matter (DM) self-annihilation during the cooling and subsequent collapse of the metal-free gas, in haloes hosting the formation of the first stars in the Universe. We find that the feedback induced on the chemistry of the cloud does modify the properties of the gas throughout the collapse. However, the modifications are not dramatic, and the typical Jeans mass within the halo is conserved throughout the collapse, for all the DM parameters we have considered. This result implies that the presence of DM annihilations does not substantially modify the initial mass function of the first stars, with respect to the standard case in which such additional energy term is not taken into account. We find also that when the rate of energy produced by the DM annihilations and absorbed by the gas equals the chemical cooling (at densities yet far from the actual formation of a protostellar core) the structure does not halt its collapse, although that proceeds more slowly by a factor smaller than few per cent of the total collapse time. © 2010 The Authors. Journal compilation © 2010 RAS.