Yellow hypergiant

massive star with an extended atmosphere

A yellow hypergiant is a huge hypergiant star. It starts off a mass of about 20–60 solar masses, but it soon loses about half that mass (because they are very unstable). It has a spectral class from A to K.

Intrinsic variable types in the Hertzsprung–Russell diagram showing the Yellow Hypergiants above (i.e. more luminous than) the Cepheid instability strip.

They are amongst the most luminous stars, with absolute magnitude (MV) around −9. They are very rare: only 15 are known in the Milky Way and six of those are in a single cluster.

They are sometimes referred to as 'cool hypergiants' in comparison to O- and B-type stars, and sometimes as 'warm hypergiants' in comparison to red supergiants. Yellow hypergiants have evolved off the main sequence and have little hydrogen left in their centres.