Light–Gravity Bounds: From Stellar Envelopes to Black Hole Horizons

This study develops a unified framework for radiation–gravity bounds that apply from luminous stars to black hole horizons. At the stellar scale, the Eddington timescale provides a universal upper bound on radiation–driven envelope expansion. Observations of luminous blue variables confirm that real stars evolve much faster, establishing τ_Edd as a theoretical ceiling rather than a predictive timescale. General relativistic corrections extend this law to compact objects: the relativistic Eddington luminosity decreases with compactness, and the corrected timescale diverges as a black hole horizon is approached. This connects classical stellar physics with horizon thermodynamics, offering a common language for radiation–gravity interactions across astrophysics. The framework highlights how fundamental constants set the ultimate limits for envelope expansion, stability, and collapse.