Little Red Dots Show Black Hole Seeds of 10^4-5 Solar Masses Consistent with Supermassive Star Collapse

The study fits stellar atmosphere models to host-subtracted LRD continua, deriving effective temperatures of 4200-4800 K and photospheric radii of 700-2000 au. Four independent mass estimators—surface gravity, super-Eddington scaling, outflow escape velocity, and variability dynamical time—converge on the same 10^4-5 M⊙ range. This resolves the reported 2-3 dex offset above the local scaling relation without invoking exotic growth channels.

Conventional direct-collapse or stellar-remnant merger scenarios struggle to produce seeds this massive at z>6 while respecting general-relativistic instability limits near 10^5-6 M⊙. The observed luminosity-function cutoff aligns precisely with the theoretical maximum SMS mass, suggesting LRDs capture the brief, luminous phase of seed formation. The pseudo-photosphere interpretation also explains the lack of strong X-ray and variability signatures that plague standard AGN models.

Methods note: stacked spectra of 117 objects fitted with tailored stellar atmospheres; key limitation is reliance on stacks rather than individual high-S/N spectra, which could mask diversity. JWST/NIRSpec follow-up of unlensed LRDs at higher resolution would test whether the temperature and radius distributions remain narrow.

Next steps include targeted ALMA and Chandra observations to constrain outflow masses and X-ray weakness, plus comparison against emerging hydrodynamical simulations of SMS collapse that predict specific luminosity-function slopes at z=5-8.