Density spikes near black holes in self-interacting dark matter halos and indirect detection constraints

Self-interacting dark matter (SIDM) naturally gives rise to a cored isothermal density profile, which is favored in observations of many dwarf galaxies. The dark matter distribution in the presence of a central black hole in an isothermal halo develops a density spike with a power law of r(-7/4), which is shallower than r(-7/3) as expected for collisionless dark matter (CDM). Thus, indirect detection constraints on dark matter annihilations from the density spike could be relaxed in SIDM. Taking the most dense satellite galaxy of the Milky Way Draco as an example, we derive upper limits on the annihilation cross section and the black hole mass for both SIDM and CUM halos. For the former case, Draco could host an intermediate mass black hole even if dark matter is composed of thermal relics. We further explore the constraints from the Milky Way and M87, which host supermassive black holes, and show the upper limits on the annihilation cross section are significantly weakened in SIDM. Our results also indicate that the Event Horizon Telescope could provide a unique test of SIDM spikes.

Automated summary

The study suggests that self-interacting dark matter (SIDM) may lead to shallower density spikes, resulting in relaxed constraints on indirect detection of dark matter annihilation. By examining satellite galaxies like Draco in the Milky Way, upper limits on the annihilation cross section and black hole mass for both SIDM and CUM halos are derived. Constraints on dark matter annihilation are significantly weakened in SIDM, especially in the presence of supermassive black holes in galaxies like the Milky Way and M87.