Little red dots as embryos of active galactic nuclei

Jian-Min Wang, Yi-Lin Wang, Yong-Jie Chen, Jun-Rong Liu, Yu-Yang Songsheng, Cheng Cheng, Yan-Rong Li, Pu Du, Hao Zhang, Yu Zhao

First listed 2025-11-12 | Last updated 2025-11-12

Abstract

As an unprecedented large population in the early universe, the JWST-discovered little red dots (LRDs) have garnered much attention for formation of massive black holes and galaxies, but their nature remains a mystery. The LRDs appearing as ``Chimeras" like both active galactic nuclei (AGNs) and galaxies have stimulated renewed interest in the roadmap of central massive black hole (cMBH) formation in AGNs. In this paper, we suggest that the LRDs contain $M_{\bullet}\lesssim 10^6\,M_{\odot}$ cMBHs as demonstrated by the Sołtan argument and there is a large population of stellar-mass black holes (sMBHs with total mass of $\mathscr{M}_{m_{\bullet}}$) embedded inside cMBH accretion disks (cMBH-disk) as motivated by anomalous reverberations of broad H$β$ line in local AGNs. This embryo structure of LRDs ($M_{\bullet}<\mathscr{M}_{m_{\bullet}}$) is formed as a consequence of gravitational collapse of primordial clouds. In this Chimera, accretion onto sMBHs powers the rest-frame optical continuum of the LRDs but the UV continuum is jointly contributed by slim parts of the cMBH-disks and nuclear starbursts in the core of collapsing clouds governing the appearance of the observed V-shaped spectral energy distributions (SEDs). Outflowing clumped-envelopes are unavoidably formed by radiation pressure leading to absorption features of the Balmer lines. The present model works very well for LRDs' SEDs and avoids the issues of overly massive cMBHs. Evolution of LRDs is briefly discussed including gravitational waves.

Short digest

This paper proposes that JWST little red dots are embryos of AGN in which a modest central massive black hole (M_bh ≲ 10^6 Msun) is embedded within a cMBH disk that hosts a large population of stellar-mass black holes. Invoking the Sołtan argument, the authors argue these lighter cMBHs resolve overmassive-BH tensions, while accretion onto embedded sMBHs powers the rest-frame optical and slim cMBH disks plus nuclear starbursts shape the UV, yielding the hallmark V-shaped SEDs. Radiation-pressure–driven clumpy envelopes naturally produce Balmer-line absorption troughs. The model reproduces representative LRD SEDs and offers a growth pathway consistent with black-hole mass density constraints.

Key figures to inspect

• Figure 1: Use the schematic to map where the slim cMBH disk ends and the s@cMBH-disk begins, and see how a clumpy outflow along the line of sight generates Balmer absorption; note the embryo mass hierarchy with M_bh smaller than the summed sMBH mass.
• Figure 2: Inspect SED fits that require three components; verify that the nuclear starburst specifically fills the flux around the Balmer break while the s@cMBH-disk dominates the optical and the slim disk shapes the far-UV, producing the V-shaped continuum.
• Figure 3: Compare SEDs fit without a nuclear starburst; check how the combination of slim cMBH disk and s@cMBH-disk alone reproduces the V-shape and what this implies for minimal starburst contribution.
• Figure 4: Examine cases needing multiple nuclear starbursts and sometimes no slim disk, implying very light cMBHs; note the P Cygni Balmer profile in RUBIES-EGS 42046 as evidence for the proposed outflowing clumps.