Formation of the Little Red Dots from the Core-collapse of Self-interacting Dark Matter Halos

Abstract

We present a statistical study of black hole (BH) formation and growth seeded by gravothermal core collapse of self-interacting dark matter (SIDM) halos at high redshift, using a cosmological semi-analytical framework based on Monte Carlo merger trees. We demonstrate that gravothermal collapse naturally leads to BH formation in high-concentration halos at a characteristic mass scale set by the SIDM cross section, and occurs predominantly in the early Universe. This mechanism is particularly promising for explaining the abundance of the little red dots (LRDs) -- a population of early, apparently galaxy-less active galactic nuclei hosting supermassive BHs. By incorporating this seeding process with simple models of BH growth and assuming a 100% duty cycle, we reproduce the observed LRD mass function for velocity-dependent cross sections of $\sigma_{0m} \sim 30\,\mathrm{cm}^2\,\mathrm{g}^{-1}$ and $\omega \sim 80\,\mathrm{km}\,\mathrm{s}^{-1}$, which are consistent with independent constraints from local galaxies. While higher values of $\sigma_{0m}$ (or $\omega$) would overpredict the low-mass (or high-mass) end of the BH mass function, such deviations could be reconciled by invoking a reduced duty cycle or lower Eddington ratio. Our results suggest that the demographics of high-redshift BHs can serve as a novel and complementary probe of SIDM physics.