Editing Supergiant (section)

===Evolutionary supergiants===
Supergiants can also be defined by a specific phase in the evolutionary history of certain stars. Stars with initial masses above {{solar mass|8-10}} quickly and smoothly initiate helium-core fusion after they have exhausted their hydrogen, and continue fusing heavier elements after helium exhaustion until they develop an iron core, at which point the core collapses to produce a [[Type II supernova]].  Once these massive stars leave the main sequence, their [[Stellar atmosphere|atmospheres]] inflate, and they are described as supergiants.  Stars initially under {{solar mass|10}} will never form an iron core and in evolutionary terms do not become supergiants, although they can reach luminosities thousands of times the Sun's. They cannot fuse carbon and heavier elements after the helium is exhausted, so they eventually just lose their outer layers, leaving the core of a [[white dwarf]].  The phase where these stars have both hydrogen- and helium-burning shells is referred to as the [[asymptotic giant branch]] (AGB), as stars gradually become more and more luminous class M stars.  Stars of {{solar mass|8-10}} may fuse sufficient carbon on the AGB to produce an oxygen-neon core and an [[Supernova#Core collapse|electron-capture supernova]], but astrophysicists categorise these as super-AGB stars rather than supergiants.<ref>{{cite journal|bibcode=2006ASPC..353..211V|arxiv=astro-ph/0512326|title=On the metallicity dependence of the winds from red supergiants and Asymptotic Giant Branch stars|journal=Stellar Evolution at Low Metallicity: Mass Loss|volume=353|pages=211–224|last1=Van Loon|first1=J. Th.|year=2006}}</ref>