The structure of dark matter halos in an annihilating dark matter model

Abstract

The inability of standard non-interacting cold dark matter (CDM) to account for the small scale structure of individual galaxies has led to the suggestion that the dark matter may undergo elastic and/or inelastic scattering. We simulate the evolution of an isolated dark matter halo which undergoes both scattering and annihilation. Annihilations produce a core that grows with time due to adiabatic expansion of the core as the relativistic annihilation products flow out of the core, lessening the binding energy. An effective annihilation cross section per unit mass equal to 0.03 cm 2 g −1 (100 km s −1/ v) with a scattering cross section per unit mass of 0.6 cm g −1 produces a 3 kpc core in a 10 10 M ⊙ halo that persists for 100 dynamical times. The same cross section leads to a core of only 120 pc in a rich cluster. In addition to creating to cores, annihilation should erase structure on scales below ∼3×10 8 M ⊙. Annihilating dark matter provides a mechanism for solving some of the problems of non-interacting CDM, at the expense of introducing a contrived particle physics model.