Luminous blue variable

Luminous blue variables, also known as S Doradus variables, are very bright, blue, hypergiant variable stars named after S Doradus, the brightest star of the Large Magellanic Cloud. They exhibit long, slow changes in brightness, punctuated by occasional outbursts in brightness during substantial mass loss events (e.g. Eta Carinae, P Cygni). They are extraordinarily rare. The General Catalogue of Variable Stars only lists 20 objects as SDor.^[1]

LBVs can shine millions of times brighter than the Sun and, with masses up to 150 times that of the Sun, approach the theoretical upper limit for stellar mass, making them among the most luminous, hottest and most energy-releasing stars in the universe. If they were any larger, their gravity would be insufficient to balance their radiation pressure and they would blow away the excess mass through stellar wind. As they are, they barely maintain hydrostatic equilibrium because their stellar wind constantly ejects matter, decreasing the mass of the star. For this reason, there are usually nebulae around such stars, created by these outbursts; Eta Carinae is the nearest and best-studied example. Because of their large mass and high luminosity, their lifetime is very short — only a few million years.

Current theory holds that LBVs are a stage in the evolution of very massive stars required for them to shed excess mass.^[2] They may evolve to Wolf-Rayet Stars before exploding into supernovae. If the star does not lose enough mass, it may undergo a particularly powerful supernova created by pair-instability.

Some models suggest that LBV 1806-20 or the Pistol Star may be the most luminous stars known. Outburst by LBVs can produce Supernova impostors.

List of LBVs

• Eta Carinae
• Pistol Star
• LBV 1806-20
• P Cygni
• S Doradus
• HD 269858 (= R127)
• HD 269006 (= R71)
• AG Carinae
• Wray 17-96
• AF Andromedae
• AE Andromedae
• HD 5980
• Sanduleak -69° 202; no longer exists: the star exploded as SN 1987A

See also

• Hypernova

References

1. ^ "GCVS Variability Types". General Catalogue of Variable Stars @ Sternberg Astronomical Institute, Moscow, Russia. 12-Feb-2009. http://www.sai.msu.su/gcvs/gcvs/iii/vartype.txt. Retrieved 2010-11-24. 
2. ^ Smith, Nathan & Owocki, Stanley (2006). "On the Role of Continuum-driven Eruptions in the Evolution of Very Massive Stars and Population III Stars". Astrophysical Journal 645 (1): L45. arXiv:astro-ph/0606174. Bibcode 2006ApJ...645L..45S. doi:10.1086/506523. 

External links

• GCVS: List of SDOR variable stars