Luminous Blue Variable Star - Evolution

Evolution

Because of their large mass and high luminosity, their lifetime is very short—only a few million years in total and much less than a million years in the LBV phase. They are rapidly evolving on timescales that we can observe; examples have been detected where stars with Wolf-Rayet spectra (WNL/Ofpe) have developed to show LBV outbursts and a handful of supernovae have been traced to likely LBV progenitors.

There appear to be two groups of LBVs, one with luminosities above 630,000 times the sun and the other with luminosities below 400,000 times the sun. Models have been constructed. showing that the lower luminosity group are post-red supergiant stars with masses of 30–60 times the sun, while the higher luminosity group are population II stars with masses 60–90 times the sun which never develop to red supergiants although they may become yellow hypergiants. Some models hold that LBVs are a stage in the evolution of very massive stars required for them to shed excess mass while others require that most of the mass is lost at an earlier cool supergiant stage. Normal outbursts and the stellar winds in the quiescent state are not sufficient for the required mass loss, but LBVs occasionally produce abnormally large outbursts that can be mistaken for a faint supernova and these may shed the necessary mass. Recent models all agree that the LBV stage occurs after a hydrogen-rich Wolf-Rayet stage and before a hydrogen-poor Wolf-Rayet stage, and that almost all will eventually end as a supernova. They apparently can explode directly as a supernova although that isn't easily predicted by theory. If the star does not lose enough mass before the end of the LBV stage, it may undergo a particularly powerful supernova created by pair-instability.