= Solution
The exact initial-mass boundaries depend on metallicity, convective overshooting, rotation, and mass loss, but stars near the upper intermediate-mass range, roughly $6.5$--$9M_\odot$, can become <Super-AGB stars>. They ignite carbon but do not immediately ignite neon hydrostatically throughout the core.
Their final fate is set by competition between shell-driven core growth and envelope loss. If a <stellar wind> removes the envelope first, the remnant is an oxygen-neon, or oxygen-neon-magnesium, <white dwarf>. If the degenerate core grows toward the <Chandrasekhar mass>, electron captures on magnesium and neon reduce the electron pressure and can trigger an <electron-capture supernova>, leaving a <neutron star>. Slightly higher-mass stars can ignite further fuels and proceed to ordinary iron-core collapse.
Back to article page
