Editing Supergiant (section)

===Temperature===
There are supergiant stars at all of the main spectral classes and across the whole range of temperatures, from mid-M class stars at around 3,400 K to the hottest O class stars over 40,000 K.  Supergiants are generally not found cooler than mid-M class.  This is expected theoretically since they would be catastrophically unstable; however, there are potential exceptions among extreme stars such as [[VX Sagittarii]].<ref name=levesque>{{cite journal|bibcode=2005ApJ...628..973L|arxiv=astro-ph/0504337|title=The Effective Temperature Scale of Galactic Red Supergiants: Cool, but Not As Cool As We Thought|journal=The Astrophysical Journal|volume=628|issue=2|pages=973–985|author1-link=Emily Levesque|last1=Levesque|first1=Emily M.|last2=Massey|first2=Philip|last3=Olsen|first3=K. A. G.|last4=Plez|first4=Bertrand|last5=Josselin|first5=Eric|last6=Maeder|first6=Andre|last7=Meynet|first7=Georges|year=2005|doi=10.1086/430901|s2cid=15109583}}</ref>

Although supergiants exist in every class from O to M, the majority are spectral type B (blue supergiants), more than all other spectral classes combined. A much smaller grouping consists of very low-luminosity G-type supergiants, intermediate-mass stars burning helium in their cores before reaching the [[asymptotic giant branch]].  A distinct grouping is made up of high-luminosity supergiants at early B (B0-2) and very late O (O9.5), more common even than main-sequence stars of those spectral types.<ref name=sowell>{{cite journal|bibcode=2007AJ....134.1089S|title=H-R Diagrams Based on the HD Stars in the Michigan Spectral Catalogue and the Hipparcos Catalog|journal=The Astronomical Journal|volume=134|issue=3|pages=1089|last1=Sowell|first1=J. R.|last2=Trippe|first2=M.|last3=Caballero-Nieves|first3=S. M.|last4=Houk|first4=N.|year=2007|doi=10.1086/520060|doi-access=free}}</ref> The number of post–main-sequence blue supergiants is greater than those expected from theoretical models, leading to the "blue supergiant problem".<ref>{{cite journal |last1=Bellinger |first1=Earl Patrick |title=The Potential of Asteroseismology to Resolve the Blue Supergiant Problem |date=2024 |arxiv=2311.00038 |last2=de Mink |first2=Selma E. |last3=van Rossem |first3=Walter E. |last4=Justham |first4=Stephen|journal=The Astrophysical Journal |volume=967 |issue=2 |pages=L39 |doi=10.3847/2041-8213/ad4990 |doi-access=free |bibcode=2024ApJ...967L..39B }}</ref>

The relative numbers of blue, yellow, and red supergiants serve as an indicator of the speed of stellar evolution and are used as a powerful test of models of the evolution of massive stars.<ref name=massey>{{cite journal|bibcode=2003AJ....126.2867M|arxiv=astro-ph/0309272|title=The Evolution of Massive Stars. I. Red Supergiants in the Magellanic Clouds|journal=The Astronomical Journal|volume=126|issue=6|pages=2867–2886|last1=Massey|first1=Philip|last2=Olsen|first2=K. A. G.|year=2003|doi=10.1086/379558|s2cid=119476272}}</ref>