Luminous blue variable

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Luminous blue variables, also known as S Doradus variables, are very bright, blue, hypergiant variable stars. They exhibit long, slow changes in brightness, punctuated by occasional outbursts of substantial mass loss. They are extraordinarily rare.

They 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. If they were any larger, their gravity would be insufficient to balance their radiation pressure and they would blow themselves apart. 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.^[1] They may evolve to Wolf-Rayet Stars before going supernova. If the star does not lose enough mass, it may undergo a particularly powerful supernova created by pair-instability.