Large-amplitude isothermal fluctuations and high-density dark-matter clumps

Abstract

Large-amplitude isothermal fluctuations in the dark matter energy density, parameterized by $Φ\equivδ\rhodm/\rhodm$, are studied within the framework of a spherical collapse model. For $Φ\ga 1$, a fluctuation collapses in the radiation-dominated epoch and produces a dense dark-matter object. The final density of the virialized object is found to be $ρ_F \approx 140\, Φ^3 (Φ+1) \rhoeq$, where $\rhoeq$ is the matter density at equal matter and radiation energy density. This expression is valid for the entire range of possible values of $Φ$, both for $Φ\gg 1$ and $Φ\ll 1$. Some astrophysical consequences of high-density dark-matter clumps are discussed.