Rapid emergence of overmassive black holes in the early Universe

TL;DR

This study uses advanced cosmological simulations to explain the rapid formation and growth of overmassive supermassive black holes in the early Universe, aligning with recent JWST observations.

Contribution

First self-consistent cosmological simulations demonstrating the formation of heavy black hole seeds and their rapid super-Eddington growth in proto-cluster environments.

Findings

Heavy seeds of ~10^6 solar masses naturally form.

Dense, optically thick disks produce broad Hα emission.

Super-Eddington accretion drives rapid growth to ~3×10^7 solar masses by z~8.

Abstract

The origin of supermassive black holes (SMBHs) remains a long-standing problem in astrophysics. Recent JWST observations reveal an unexpectedly abundant population of overmassive black holes at z>4-6, where the BH masses lie far above local scaling relations and not reproduced by current cosmological models. How such overmassive black holes form and rapidly grow within young galaxies has remained unclear. Here we present fully cosmological radiation-hydrodynamic simulations that, for the first time, self-consistently follow the birth, early growth, and emergent observable signatures of SMBHs in proto-cluster environments. We find that heavy seeds of order $10^6 M_\text{sun}$ naturally form, exceeding typical theoretical expectations by an order of magnitude. These seeds rapidly develop dense, optically thick disks whose strong electron scattering produces broad H$\alpha$ emission comparable to that seen in little red dots (LRDs). Sustained super-Eddington accretion then drives fast growth to $\sim 3 \times 10^7 ~M_\text{sun}$ by $z \sim 8$. These results provide a unified physical scenario in which LRDs correspond to a short-lived, enshrouded phase of heavy-seed formation, naturally evolving into the overmassive quasars detected by JWST and ultimately the progenitors of today's SMBHs.