SUPERMASSIVE BLACK HOLES FROM ULTRA-STRONGLY SELF-INTERACTING DARK MATTER

We consider the cosmological consequences if a small fraction (f less than or similar to 0.1) of the dark matter is ultra-strongly self-interacting, with an elastic self-interaction cross section per unit mass sigma >> 1 cm(2)g(-1). This possibility evades all current constraints that assume that the self-interacting component makes up the majority of the dark matter. Nevertheless, even a small fraction of ultra-strongly self-interacting dark matter (uSIDM) can have observable consequences on astrophysical scales. In particular, the uSIDM subcomponent can undergo gravothermal collapse and form seed black holes in the center of a halo. These seed black holes, which form within several hundred halo interaction times, contain a few percent of the total uSIDM mass in the halo. For reasonable values of sigma f, these black holes can form at high enough redshifts to grow to similar to 10(9) M-circle dot quasars by z greater than or similar to 6, alleviating tension within the standard Lambda cold dark matter cosmology. The ubiquitous formation of central black holes in halos could also create cores in dwarf galaxies by ejecting matter during binary black hole mergers, potentially resolving the too big to fail problem.