Supergiants are stars with between 10 and 70 solar masses. They are among the most massive stars known, located at the top of the Hertzsprung-Russell diagram, which maps star luminosity against spectral type. Like most other star types, supergiants come in all colors: red supergiants, blue supergiants, yellow supergiants, etc. They live fast (10-50 million years) and die hard (forming a black hole or neutron star after a supernova).
Stars even more massive than supergiants, in the range of 70 to 120 solar masses, are called hypergiants. Stars much more massive than 120 solar masses cannot exist because they blow themselves apart with nuclear reactions before they can fully form. The more massive a star is, the more intense its solar wind is, and the more of its mass it loses. The short-lived and very massive Wolf-Rayet supergiant stars are the most intense cosmic geysers known, ejecting 10-3% of their mass into the interstellar medium each year at speeds of up to 2000 km/s.
Because they last only 10-50 million years, supergiants tend to be found in relatively young cosmic structures such as open clusters, the arms of spiral galaxies, and in irregular galaxies. They are rarely found in elliptical galaxies which primarily contain old stars. Our Sun, much less massive than a supergiant, is expected to have a total lifespan of about 9 billion years before it transforms into a red giant, which is less massive than a supergiant but still very large in diameter.
Supergiants tend to have radii about 30 to 500 times larger than the Sun, but sometimes as huge as 1000 times larger and above, as in the case of VY Canis Majoris and VV Cephei. In all, giant stars are separated into the categories of giant, supergiant, and hypergiant. Each has distinct pathways of stellar evolution. The more massive a star is, the shorter it lives, and the more likely it is to ultimately collapse into a black hole.
By Michael Anissimov