Dark matter densities during the formation of the first stars and in dark stars

Abstract

The first stars in the universe form inside ∼106 M ⊙ dark matter (DM) halos whose initial density profiles are laid down by gravitational collapse in hierarchical structure-formation scenarios. During the formation of the first stars in the universe, the baryonic infall compresses the DM further. The resultant DM density is presented here, using an algorithm originally developed by Young to calculate changes to the profile as a result of adiabatic infall in a spherical halo model; the Young prescription takes into account the noncircular motions of halo particles. The density profiles obtained in this way are found to be within a factor of 2 of those obtained using the simple adiabatic contraction prescription of Blumenthal and colleagues. Our results hold regardless of the nature of the DM or its interactions and rely merely on gravity. If the DM consists of weakly interacting massive particles, which are their own antiparticles, their densities are high enough that their annihilation in the first protostars can indeed provide an important heat source and prevent the collapse all the way to fusion. In short, a "Dark Star" phase of stellar evolution, powered by DM annihilation, may indeed describe the first stars in the universe. © 2009. The American Astronomical Society. All rights reserved.