Scale selection in gravitational collapse: an equation-of-state-independent bound on compact-object radii

We derive an equation-of-state-independent lower bound on the radius achievable during gravitational collapse with angular momentum: R ≥ J²/(2αkGM³). The bound follows from angular momentum conservation under three conservative assumptions and makes no reference to nuclear physics or any specific equation of state. We identify a quantitative boundary separating dynamics-dominated and EOS-dominated collapse regimes, and show that for neutron-mass fermion systems the centrifugal and degeneracy scales independently converge to the same order of magnitude, providing a structural explanation for the narrow radius range of neutron stars. Numerical evaluation with independently constrained stellar parameters demonstrates consistency with NICER X-ray timing measurements.