Primordial Black Holes as Seeds for Extremely Overmassive Active Galactic Nuclei Observed by JWST

Abstract The James Webb Space Telescope (JWST) has recently identified A2744–QSO1 as a compact, metal-poor, black hole (BH)–dominated galaxy at z ≃ 7. This system exhibits an extreme black-hole-to-stellar mass ratio and unusually low metallicity, posing significant challenges to BH seeding models. Motivated by these discoveries, we perform high-resolution cosmological simulations with a massive primordial black hole (PBH; M BH = 5 × 10 7 M ⊙ ) seed, incorporating for the first time a fully coupled treatment of PBH accretion, BH feedback, and Population III/II star formation and stellar feedback. Although PBHs accelerate structure formation through the seed effect, the associated strong thermal feedback from the accretion delays the onset of star formation to z ≲ 10, producing short, bursty episodes throughout the subsequent evolution. PBH-driven outflows expel enriched gas from the nucleus, while sustained inflows from the intergalactic medium continuously replenish pristine material. This feedback-regulated cycle naturally yields low accretion rates ( m ̇ BH / m ̇ edd ∼ 1 % − 10 % ), subsolar metallicities ( Z / Z ⊙ ≲ 10 −2 ), and extreme M BH / M ⋆ ratios during both the initial star-forming phase and the subsequent quenching phases, in excellent agreement with JWST observations. Our results demonstrate that massive PBHs offer a viable pathway for forming the most extreme high-redshift systems, providing a physically motivated explanation for the extraordinary properties of A2744–QSO1, as a subclass of the broader population of JWST-discovered “little red dots.”