hypergiant

A hypergiant (luminosity class 0) is a star with a tremendous mass and luminosity, showing signs of a very high rate of mass loss.

The word "hypergiant" is commonly used as a loose term for the most massive stars found, even though there are more precise definitions. In 1956, the astronomers Feast and Thackeray used the term super-supergiant (later changed into hypergiant) for stars with an absolute magnitude greater than M_V = −7. In 1971, Keenan suggested that the term would be used only for supergiants showing at least one broad emission component in Hα, indicating an extended stellar atmosphere or a relatively large mass loss rate. The Keenan criterion is the one most commonly used by scientists today. This means that a hypergiant does not necessarily have to be more massive than a similar supergiant. Still, the most massive stars are considered to be hypergiants, and can have masses ranging up to 100–265 solar masses.