Two Hubble Space Telescope images are overlain onto an artist impression of the
internal structure of a super-AGB star. The super-AGB star is a red giant star,
with a compact core surrounded by nuclear burning helium and hydrogen shells
and a large convective mantle. It is not clear how it comes to an end: it may
leave a neon-rich white dwarf illuminating a Planetary Nebula (top picture), or
explode as a supernova as shown in the bottom picture of a supernova remnant.