Hybrid Simulations Reveal Viable IMBH Pathway to High-Redshift SMBHs, But Rest on Optimistic Assumptions

This arXiv preprint (v1, 8 Jun 2026) presents the first self-consistent hybrid hydro/direct N-body runs with Enzo-Abyss that couple gas dynamics, stellar evolution, and direct gravitational integration to show runaway stellar collisions in metal-poor, turbulent clouds produce very massive stars (343–5108 M⊙) that collapse into IMBHs. The study models star-cluster-scale systems resembling JWST-detected dense high-z nuclear star cluster precursors, finding IMBHs that accrete at 1.64×10^{-4} M⊙ yr^{-1} with TDEs supplying 23 % of growth over 10 Myr; projecting forward under steady gas inflow yields a 6747 M⊙ seed reaching ~62 000 M⊙ in 100 Myr. While the methodology—varying turbulence and wind feedback across multiple cloud realizations—avoids ad-hoc seeds, it remains a preprint lacking peer review and relies on a single code framework with limited parameter sweeps; the constant TDE rate and uninterrupted gas supply assumptions may overestimate growth when realistic feedback and mergers are included. This work bridges the gap between classic runaway-collision studies (e.g., Portegies Zwart et al. 2004 on young clusters) and SMBH seed requirements for z>6 quasars (Volonteri 2010), highlighting how JWST’s compact high-z sources could be the direct progenitors missed by purely analytic or lower-resolution cosmological simulations.