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 semianalytical 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)—early active galactic nuclei whose BHs appear dramatically overmassive relative to their host galaxies. By incorporating this seeding process with simple models of BH growth and assuming a 100% duty cycle, we broadly reproduce the observed LRD mass function for velocity-dependent cross sections of σ 0 m ∼ 30 cm 2 g −1 and ω ∼ 80 km s −1 , which are consistent with independent constraints from local galaxies. While higher values of σ 0 m (or ω ) 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.