Editing Star (section)

====Massive stars====
{{Main|Supergiant star|Hypergiant|Wolf–Rayet star}}
[[File:Layers of an evolved star.png|thumb|upright=1.6|Onion-like layers at the core of a massive, evolved star just before core collapses]]
During their helium-burning phase, a star of more than 9 solar masses expands to form first a [[blue supergiant]] and then a [[red supergiant]]. Particularly massive stars (exceeding 40 solar masses, like [[Alnilam]], the central blue supergiant of [[Orion's Belt]])<ref>{{Cite journal |last1=Puebla |first1=Raul E. |last2=Hillier |first2=D. John |last3=Zsargó |first3=Janos |last4=Cohen |first4=David H. |last5=Leutenegger |first5=Maurice A. |date=2016-03-01 |title=X-ray, UV and optical analysis of supergiants: &epsilon; Ori |journal=Monthly Notices of the Royal Astronomical Society |volume=456 |issue=3 |pages=2907–2936 |doi=10.1093/mnras/stv2783 |doi-access=free |issn=0035-8711|arxiv=1511.09365 }}</ref> do not become red supergiants due to high mass loss.<ref>{{Cite journal |last1=Vanbeveren |first1=D. |last2=De Loore |first2=C. |last3=Van Rensbergen |first3=W. |date=1998-12-01 |title=Massive stars |url=https://doi.org/10.1007/s001590050015 |journal=The Astronomy and Astrophysics Review |language=en |volume=9 |issue=1 |pages=63–152 |doi=10.1007/s001590050015 |bibcode=1998A&ARv...9...63V |issn=1432-0754}}</ref> These may instead evolve to a [[Wolf–Rayet star]], characterised by spectra dominated by emission lines of elements heavier than hydrogen, which have reached the surface due to strong convection and intense mass loss, or from stripping of the outer layers.<ref name="ContiLoore2012">{{cite book |last1=Conti |first1=P. S. |url=https://books.google.com/books?id=aZbnCAAAQBAJ |title=Mass Loss and Evolution of O-Type Stars |last2=de Loore |first2=C. |date=2012 |publisher=Springer Science & Business Media |isbn=978-94-009-9452-2}}</ref>

When helium is exhausted at the core of a massive star, the core contracts and the temperature and pressure rises enough to fuse [[carbon]] (see [[Carbon-burning process]]). This process continues, with the successive stages being fueled by [[neon]] (see [[neon-burning process]]), [[oxygen]] (see [[oxygen-burning process]]), and [[silicon]] (see [[silicon-burning process]]). Near the end of the star's life, fusion continues along a series of onion-layer shells within a massive star. Each shell fuses a different element, with the outermost shell fusing hydrogen; the next shell fusing helium, and so forth.<ref>
{{cite web |url= https://www.e-education.psu.edu/astro801/content/l6_p5.html |title=The Evolution of Massive Stars and Type II Supernovae |publisher=Penn Stats College of Science |access-date= 2016-01-05}}
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The final stage occurs when a massive star begins producing iron. Since iron nuclei are more [[binding energy|tightly bound]] than any heavier nuclei, any fusion beyond iron does not produce a net release of energy.<ref name="sneden">{{Cite journal |title= Astronomy: The age of the Universe |journal= Nature |date= 2001-02-08  |pages= 673–675 |volume= 409 |issue= 6821 |doi= 10.1038/35055646 |pmid= 11217843 |first= Christopher |last= Sneden|s2cid= 4316598 |doi-access= free }}</ref>

Some massive stars, particularly [[luminous blue variable]]s, are very unstable to the extent that they violently shed their mass into space in events known as [[supernova impostor]]s, becoming significantly brighter in the process. [[Eta Carinae]] is known for having undergone a supernova impostor event, the Great Eruption, in the 19th century.