Growth of High-Redshift Quasars from Fermion Dark Matter Seeds

Yu Wang, Remo Ruffini

First listed 2026-02-04 | Last updated 2026-02-04

Abstract

Quasars hosting $\gtrsim 10^{9}\,M_\odot$ black holes at $z>6$ challenge growth scenarios that start from light seeds and assume accretion within already formed galaxies. Motivated by the James Webb Space Telescope (JWST) discovery of Little Red Dots (LRDs), which suggests that $\sim 10^{6}\,M_\odot$ black holes can be active in compact, pre-galactic environments, we revisit early black hole growth with a minimal cosmology-based framework. We model the accretion history as the smaller of the Bondi inflow rate and the Eddington-limited rate, where the Bondi rate is set by the supply of overdense primordial gas whose density declines with cosmic expansion, and the Eddington rate captures regulation by radiative feedback. By fitting the observed masses and luminosities of J0313--1806 ($z=7.64$) and J0100+2802 ($z=6.30$) with Bayesian inference, we infer initial conditions that favor massive seed black holes with initial mass $M_0 \sim 10^{6}\,M_\odot$, formed at $z\sim20{-}30$ in environments with baryonic overdensity factors $f_ρ\gtrsim 50$ relative to the cosmic mean. The resulting growth histories include a prolonged supply-limited stage, and they reproduce the observed quasar masses without requiring sustained Eddington accretion or any super-Eddington episodes. The inferred seed mass scale is consistent with black holes produced by the collapse of quantum-degenerate fermion dark matter cores, providing a physically defined pathway to massive seeds at the redshifts implied by LRD phenomenology.

Short digest

Minimal, cosmology-tied growth tracks are built for z>6 quasars by taking the accretion rate as the minimum of Bondi supply from overdense primordial gas and the Eddington limit, with LRDs motivating a pre-galactic setting. Bayesian fits to J0313−1806 (z=7.64) and J0100+2802 (z=6.30) favor massive seeds, M0≈10^6 Msun, forming at z≈20–30 in regions with baryonic overdensity factors fρ≳50 relative to the mean. The histories include a long supply-limited (Bondi) stage and still reproduce the observed SMBH masses without sustained Eddington or any super‑Eddington episodes. The inferred seed scale is naturally consistent with collapse of quantum‑degenerate fermion–DM cores, offering a concrete LRD‑era pathway to early SMBHs.

Key figures to inspect

• Figure 2 (J0100+2802 posteriors): Read off the MCMC contours showing the seed‑mass–overdensity degeneracy; quantify the favored log M0≈6 and that significant fρ (≳50) is required unless seeds are heavier.
• Figure 3 (J0313−1806 history): Track when the model switches between Bondi‑limited and Eddington‑limited growth, how the Eddington ratio dips below unity and later resurges, and compare the final mass/luminosity to the z=7.64 data point; note the yellow line marking disfavored very‑early seed times.
• Figure 4 (J0100+2802 history): Examine the mass build‑up and the duration of the Bondi‑limited plateau versus near‑Eddington phases, and confirm the model reaches the observed mass at z=6.30 without super‑Eddington demands; check the preferred seed‑redshift window relative to the yellow marker.
• Figure 1 (cosmic densities vs z): Use the baryon‑density decline with expansion to understand why Bondi supply weakens with time and why overdensity fρ is pivotal for early growth in an LRD‑like environment.