The Radius Floor for a Protoneutron Star Implied by the Neutron-Branch Bound

A density bound implies a smallest possible radius for a given mass: compress a star to the bound density and it can shrink no further. For a newborn protoneutron star this paper evaluates that floor and places it beside the star's actual radius and its Schwarzschild radius. For 1.4 solar masses the floor is 4.089e-10 m, which is 9.89e-14 of the Schwarzschild radius of 4.135e+00 km, while the physical star, at about 12 km after contraction, is larger than the floor by a factor of 2.93e+13. The floor therefore lies deep inside where a horizon would form, and it can never be the radius at which a real protoneutron star stops contracting: the star is supported by pressure, or it collapses through its horizon, long before the bound is approached. Simulated from stated assumptions, not measured.