Supergiant star

(astronomy) A member of the family containing the intrinsically brightest stars, populating the top of the Hertzsprung-Russell diagram; supergiant stars occur at all temperatures from 30,000 to 3000 K and have luminosities from 10⁴ to 10⁶ times that of the sun; the star Betelgeuse is an example.

A member of a class of evolved stars that occupy the top of the Hertzsprung-Russell diagram to the right of the main sequence. The absolute visual magnitudes (M_V) of supergiants range approximately between −4 and −10, and they are the largest and brightest stars. They are recognized by their spectroscopic characteristics. For example, those in class A have narrow hydrogen lines. Supergiants are subdivided into classes Ib (M_V about −5) and Ia (M_V about −7). A “hypergiant class zero” was later added near M_V = −10; the use of transition class Ia-0 at absolute visual magnitudes near −9 is now common. Red supergiants are the largest of all stars, and at maximum can reach diameters approaching that of the orbit of Saturn.

In an evolutionary sense, supergiants are stars above about 10 solar masses and absolute visual magnitude −6 that began main-sequence life hotter than class B1 and cannot evolve to become white dwarfs. As progeny of O stars, supergiants are exceedingly rare. Supergiant masses allow further burning of carbon and oxygen to oxygen, neon, and magnesium; thence to silicon and sulfur; and thence to iron. The iron cores collapse to produce type II supernovae, the condensed remnants at the centers becoming either neutron stars or, from the most massive stars, black holes. See also Astronomical spectroscopy; Black hole; Hertzsprung-Russell diagram; Neutron star; Spectral type; Star; Stellar evolution; Supernova.