Early growth of massive black holes in dynamical dark energy models with negative cosmological constant

N. Menci, M. Castellano, P. Mukherjee, D. Roberts, P. Santini, A. A. Sen, F. Shankar

First listed 2026-02-05 | Last updated 2026-02-05

Abstract

Recent results from combined cosmological probes indicate that the Dark Energy component of the Universe could be dynamical. The simplest explanation envisages the presence of a quintessence field rolling into a potential, where the Dark Energy energy density parameter $Ω_{DE}=Ω_Λ+Ω_{x}$ results from the contribution of the ground state energy $Ω_Λ$ and the scalar field energy $Ω_{x}$. Provided that $Ω_{DE}\approx 0.7$, negative values of $Ω_Λ$ can be consistent with current measurements from cosmological probes, and could help in explaining the large abundance of bright galaxies observed by JWST at $z> 10$, largely exceeding the pre-JWST expectations in a $ΛCDM$ Universe. Here we explore to what extent such a scenario can account also for the early presence of massive Black Holes (BHs) with masses $M_{BH}\gtrsim 10^7\,M_{\odot}$ observed at $z\gtrsim 8$, and for the large over-abundance of AGN with respect to pre-JWST expectations. Our aim is not to provide a detailed description of BH growth, but rather to compute the maximal BH growth that can occur in cosmological models with negative $Ω_Λ$ under the simple assumption of Eddington-limited accretion onto initial light Black Hole seeds with mass $M_{seed}\sim 10^2\,M_{\odot}$ originated from PopIII stars. To this aim we develop a simple analytic framework to connect the growth of dark matter halos to the maximal growth of BHs within the above assumptions. We show such models can account for present observations assuming values of $Ω_Λ\approx -1$, simultaneously boosting both galaxy and AGN number counts without invoking any additional physics. This would allow us to trace the observed excess of bright and massive galaxies and the early formation of massive Black Holes and the abundance of AGN to the same cosmological origin.

Short digest

Explores whether dynamical dark-energy models with a negative cosmological constant can drive early black-hole assembly seen by JWST. Using Monte Carlo–selected w0–wa histories consistent with CMB+DESI+DES, they link halo growth to maximal, continuous Eddington accretion from ~10^2 Msun Pop III seeds and predict BH mass tracks and UV luminosity functions. Models with ΩΛ ≈ −1 reproduce ≥10^7 Msun BHs at z ≳ 8 and boost bright-galaxy and AGN counts over ΛCDM without invoking heavy seeds or super‑Eddington episodes. Caveat: results are upper limits from a simplified, maximal-growth framework rather than a full BH-galaxy coevolution model.

Key figures to inspect

• Figure 1: Inspect the w0–wa confidence contours and the ‘phantom line’ to see which DE histories are allowed by CMB+DESI+DES and where negative ΩΛ solutions live (non‑phantom vs early‑phantom regions).
• Figure 2: Track how the Monte Carlo draws map (w0, wa) to Ωm, ΩDE, and the implied ΩΛ; the ΩΛ probability distribution shows whether values near −1 dominate while still yielding ΩDE ≈ 0.7.
• Figure 3: Compare the predicted high‑z UV luminosity functions to ΛCDM and to the cited surveys across the reported redshift bins to quantify the bright‑end enhancement that underpins the galaxy‑count boost in negative‑ΩΛ cosmologies.
• Figure 4: Follow the maximal BH growth curves (Eddington‑limited from ~10^2 Msun seeds) for different ΩΛ and check which tracks reach the observed JWST/X‑ray BH masses by z ≳ 8; this tests whether ΩΛ ≈ −1 suffices without heavy seeds or super‑Eddington phases.