Blue supergiant
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Blue supergiants are supergiant stars of spectral type O.
They are extremely hot and bright, with surface temperatures of between 20,000 - 50,000°C. They typically have 10 to 50 solar masses on the Hertzsprung-Russell diagram, and can have radii in excess of 1000 solar radii. These rare and enigmatic stars are amongst the hottest, largest and brightest in the known Universe.
Because of their extreme masses they have relatively short lifespans of only 10 to 50 million years and are only observed in young cosmic structures such as open clusters, the arms of spiral galaxies, and in irregular galaxies. They are not observed in spiral galaxy cores, elliptical galaxies, or globular clusters, all of which are believed to be old.
The best known example is Rigel, the brightest star in the constellation of Orion. It has a mass of around 20 times that of the Sun and gives out more light than 60,000 suns added together.