Electron-Capture Collapse of Oxygen-Neon-Magnesium Cores and Its Shift Under the Electron-Branch Bound

Some supernovae begin not with an iron core but with an oxygen-neon-magnesium core that collapses when electron captures remove its pressure support at a sharply defined density. Because the trigger is an electron process with a density threshold, it is a natural candidate for modification by the electron-branch density bound. This paper evaluates capture-onset densities from 1e12 to 1e13 kg per cubic metre against the electron-branch bound of 2.87e+48 g per cubic centimetre. At the standard onset density of 4e12 kg per cubic metre the fraction of the bound attained is 1.39e-39, bounding any shift of the 1.37-solar-mass collapse threshold at 1.91e-39 solar masses; at the top of the scan the fraction is 3.48e-39. The electron-capture trigger is set by nuclear thresholds and the electron Fermi energy alone. Simulated from stated assumptions, not measured.