Dark Bondi Accretion Aided by Baryons and the Origin of JWST Little Red Dots

Wei-Xiang Feng, Hai-Bo Yu, Yi-Ming Zhong

First listed 2025-06-21 | Last updated 2025-06-21

Abstract

The gravothermal core collapse of self-interacting dark matter halos provides a compelling mechanism for seeding supermassive black holes in the early Universe. In this scenario, a small fraction of a halo, approximately $1\%$ of its mass, collapses into a dense core, which could further evolve into a black hole. We demonstrate that this process can account for the origin of JWST little red dots (LRDs) observed at redshifts $z\sim4-11$, where black holes with masses of $10^7{\rm\,M_\odot}$ can form within $500{\rm\,Myr}$ after the formation of host halos with masses of $10^{9}{\rm\,M_\odot}$. Even if the initial collapse region triggering general-relativistic instability has a mass on the order of one solar mass, the resulting seed can grow into an intermediate-mass black hole via Eddington accretion of baryonic gas. Subsequently, it can continue to grow into a supermassive black hole through dark Bondi accretion of dark matter particles. In this scenario, the majority of the black hole's mass originates from dark matter accretion rather than baryonic matter, naturally explaining the overmassive feature of LRDs.

Short digest

Proposes an SIDM-driven seeding pathway for JWST little red dots in which gravothermal core collapse, sped up by central baryons, makes a tiny seed that grows first via baryonic Eddington accretion and then rapidly through dark Bondi inflow of SIDM. Demonstrates that black holes can reach ~10^7 Msun within ~500 Myr after the formation of ~10^9 Msun halos at z≈4–11, with most of the final mass supplied by dark matter rather than gas. Fluid simulations with and without a Plummer-fit baryonic potential show that baryons substantially shorten the collapse timescale and establish conditions for efficient dark-sector Bondi growth. The framework naturally explains the overmassive BH-to-stellar ratios in LRDs and links them to SIDM cross sections consistent with galaxy-scale structure data.

Key figures to inspect

• Figure 1: Compare the central-density evolution with (green/magenta) and without (blue) a compact Plummer baryonic potential to see how baryons accelerate gravothermal collapse; note the solid/dashed curves to gauge the dependence on the assumed self-interaction cross section.
• Figure 2: Read off when the blue (dark Bondi) curve overtakes the orange (baryonic Eddington) contribution and how the red total track depends on the initial seed (solid vs dashed); this pinpoints the transition to DM-dominated growth in the LRD regime.
• Figure 3: Use the density, Knudsen number, and SMFP-boundary markers to trace how the baryonic potential shifts the short–mean-free-path region and boosts central densities that feed Bondi inflow; the dash-dotted curve shows where stars/gas sit relative to the SIDM core.
• Figure 4: Contrast with Fig. 3 to see how changing the SIDM cross section alters the SMFP core size, Knudsen evolution, and inner density slope, i.e., the sensitivity of dark Bondi fueling to particle physics parameters.