Photogravitational Index and G: Radiation as Geometry at the Schwarzschild Limit

This article presents a novel method for deriving the gravitational constant based on observational astrophysical parameters. Using a photogravitational index , which relates radiation (luminosity) to gravitational characteristics of stellar objects, the paper demonstrates how can be computed for stars and black holes — including a case study on Cygnus X-1. At the Schwarzschild radius, the formulation converges to a purely geometric expression, revealing a potential structural link between radiation and spatial curvature. The approach offers a simple yet general framework for interpreting the relationship between light, mass, and geometry.