A super-AGB star is massive enough to ignite carbon and form a degenerate oxygen-neon core, but initially too light to proceed directly through all advanced burning stages. Its fate depends on competition between core growth and envelope mass loss.
An oxygen-neon-magnesium core is the degenerate product of carbon burning, composed mainly of oxygen and neon with a smaller magnesium abundance. It can become an oxygen-neon white dwarf or collapse after electron captures if it approaches the Chandrasekhar mass.
An electron-capture supernova occurs when electron captures, especially on neon and magnesium nuclei in a degenerate oxygen-neon core, remove pressure support and trigger collapse before ordinary iron-core formation.
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A Super-AGB star is a type of massive star that represents an extended evolutionary phase beyond the asymptotic giant branch (AGB) stage. These stars typically have initial masses in the range of about 9 to 11 solar masses, placing them between the more common AGB stars and the more massive types of stars, such as supernova progenitors.