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 ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mover accent="true"> <mml:mi>m</mml:mi> <mml:mo>̇</mml:mo> </mml:mover> <mml:mi>BH</mml:mi> </mml:msub> <mml:mo>/</mml:mo> <mml:msub> <mml:mover accent="true"> <mml:mi>m</mml:mi> <mml:mo>̇</mml:mo> </mml:mover> <mml:mi>edd</mml:mi> </mml:msub> <mml:mo>∼</mml:mo> <mml:mn>1</mml:mn> <mml:mo>%</mml:mo> <mml:mo>−</mml:mo> <mml:mn>10</mml:mn> <mml:mo>%</mml:mo> </mml:math> ), 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.”