Dark matter annihilation effects on the first stars
نویسندگان
چکیده
We study the effects of WIMP dark matter (DM) on the collapse and evolution of the first stars in the Universe. Using a stellar evolution code, we follow the pre-Main Sequence (MS) phase of a grid of metal–free stars with masses in the range 5M⊙ ≤ M∗ ≤ 600M⊙ forming in the centre of a 10 6M⊙ halo at z = 20. DM particles of the parent halo are accreted in the proto-stellar interior by adiabatic contraction and scattering/capture processes, reaching central densities of O(10 GeV cm) at radii of the order of the AU: energy release from annihilation reactions can effectively counteract the gravitational collapse. This induces a transient stalling phase (i.e. a dark star) lasting from 2.1×10yr (M∗ = 600M⊙) to 1.8×10 yr (M∗ = 9M⊙). Later in the evolution, DM scattering/capture rate becomes high enough that energy deposition from annihilations significantly alters the pre-MS evolution of the star in a way that depends on DM (i) velocity dispersion, v̄, (ii) density, ρ, (iii) elastic scattering cross section with baryons, σ0. For our fiducial set of parameters (v̄, ρ, σ0)= (10 km s , 10 GeV cm, 10 cm) we find that the evolution of stars of mass M∗ < 40M⊙ “freezes” on the HR diagram before reaching the ZAMS. Stars with M ≥ 40M⊙ manage to ignite nuclear reactions; however, DM “burning” prolonges their lifetimes by a factor 2 (5) for a 600M⊙ (40M⊙) star.
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