A Quantitative Study of Interacting Dark Matter in Halos

We study the evolution of Hernquist profile ``galaxies'' in the presence of self-interacting dark matter (SIDM), where the properties of the dark matter can be parameterized by one number, sigma-hat = sigma M/a^2 for a halo of mass M and break radius a. While the halos form constant density cores of size a/2 on the core radius relaxation time scale core collapse begins shortly thereafter and a steeper 1/r^2 central density cusp starts forming faster than predicted by 2-body relaxation. The formation of the steeper central cusp is accelerated if the cooling baryons adiabatically compress the dark matter. The natural consequence of SIDM is to exacerbate rather than to mitigate astrophysical problems created by dark matter density cusps.