Self-interacting cold dark matter halos

The evolution of halos consisting of weakly self-interacting dark matter particles is summarized. The halos initially contain a central density cusp as predicted by cosmological models. Weak self-interaction leads to the formation of an isothermal, low-density core which is in agreement with published data on the rotation curves of dwarf galaxies. However, subsequently, core collapse leads to an even steeper central density cusp. In order to explain the observed dark matter rotation curves by weak interaction, the cross section must be in a narrow range around sigma /m(p) approximate to 0.1cm(2) g(-1).