Heavy seeds ignite rapid growth, linking JWST's little red dots to overmassive black holes

Cosmological radiation‑hydrodynamic simulations show that ~10^6 solar‑mass heavy seeds can form in overdense protocluster regions under intense FUV radiation, quickly growing via brief super‑Eddington accretion to ~3×10^7 M⊙ by z ≈ 8. This unifies the high‑redshift little red dots observed by JWST with the overmassive black holes, as dense circum‑BH disks produce Balmer features and Hα emission without a traditional broad‑line region, while light‑seed remnants fail to grow similarly. The study also predicts X‑ray obscuration during early growth and potential LISA detections from BH mergers. Results are robust to changes in LW flux and higher resolution tests, offering a cohesive pathway from heavy‑seed formation to overmassive high‑z quasars.