Little Red Dots as a Transient Phase of Self-Interacting Dark Matter Assisted Black Hole Growth

Yu Rong, Shuang-Nan Zhang, Jian-Min Wang, Junxian Wang, Zhicheng He

First listed 2026-09-18 | Last updated 2026-09-17

Abstract

The discovery of Little Red Dots (LRDs) with JWST has revealed a population of compact, red galaxies hosting rapidly growing black holes at early cosmic times. Their compact morphologies, broad emission lines, weak X-ray emission, and distinctive V-shaped spectral energy distributions indicate a short-lived phase of black-hole growth within a dense nuclear environment. Here we propose that LRDs arise from a transient episode of self-interacting dark matter (SIDM)-assisted black-hole growth during galaxy assembly. In this scenario, gas inflows first establish a compact nuclear thick disk, which modifies the central SIDM distribution and provides the obscuring structure around the accreting black hole. Once the SIDM density near the seed black hole becomes sufficiently enhanced, rapid SIDM accretion drives a major increase in black-hole mass, initiating the transient LRD phase. The resulting obscured growth phase naturally suppresses direct short-wavelength emission and redistributes the radiation field, producing the red continuum and V-shaped spectral signatures of LRDs. This framework links gas inflow, SIDM dynamics, and early black-hole assembly, predicting that LRDs preferentially occur in galaxies undergoing strong nuclear inflow and evolve into ordinary AGN after this transient phase. Unlike models that require globally rare halo histories, long super-Eddington gas growth, or purely phenomenological obscuration, our model ties the overmassive black hole, X-ray weakness, spectral shape, and finite duty cycle to one local gas-triggered SIDM event.

Short digest

Rong et al. propose that little red dots are a short-lived, obscured stage of black-hole assembly triggered when a gas-rich nuclear compaction compresses self-interacting dark matter (SIDM) around a pre-existing seed. In their semi-analytic picture, a compact, optically thick thick disk both ignites rapid SIDM-fed mass growth and supplies the high-column, Balmer-active reprocessing material that produces X-ray weakness and a red, V-shaped continuum. Calibrated mock spectra reproduce the broad spectral shape and Balmer-break-like curvature of RUBIES-EGS-55604 and are also compared with RUBIES-UDS-40579, linking overmassive black holes, obscuration, and a finite LRD duty cycle to one local inflow event. The model predicts that LRDs preferentially mark galaxies in strong nuclear-inflow phases before evolving into more ordinary AGN.

Key figures to inspect

• Figure 1. This schematic is the clearest overview of the proposed causal sequence: gas inflow creates a compact thick disk, the disk compresses SIDM and triggers black-hole growth, and edge-on high-column sight lines appear as red, X-ray-weak LRDs. It usefully distinguishes the paper's coupled SIDM-plus-obscuration scenario from models in which dark-matter growth or reddening is treated separately.
• Figure 2. The fiducial RUBIES-EGS-55604 spectral comparison is the paper's central empirical demonstration. It shows how the obscured AGN, Balmer-active reprocessing photosphere, leaked young stellar light, and weak host contribution combine to reproduce the observed V-shaped continuum while masking strong emission-line regions from the continuum fit.
• Figure 3. The comparison to RUBIES-UDS-40579 tests whether the same disk-atmosphere framework extends beyond the fiducial source. Its component decomposition highlights the claimed physical origin of the red continuum: an obscured AGN plus a cooler absorbed-and-reprocessed photosphere, with only a modest leaked young-star contribution.