Supernova Triggered by Electron Captures

Abstract

Final evolution of the stars in the mass range of 8–12M◉ has been investigated fully taking account of the effects of electron captures and oxygen deflagration. Only an O–Ne–Mg core has been treated numerically from the stages well in advance of electron captures and of oxygen burning. It is found that a convective core is formed as a result of entropy production by the electron captures on 24Mg and 20Ne. It delays the onset of the oxygen deflagration to a stage with the central density as high as 2.5 × 1010 g cm−3. Because of such high densities beta processes overcome the oxygen deflagration and the core continues to contract quasi-dynamically. Behind the deflagration front the core material is processed into nuclear statistical equilibrium, from which energy is being lost by the processes of the electron captures, the photo-dissociations of nuclei, and the neutron drips. The total, i.e., the gravitational plus thermal energy of the core is decreasing at an appreciable rate. Though the numerical computation was stopped at the central density of 1 × 1011 g cm−3, it is likely that the contraction continues to form a neutron star.