The largest and brightest type of star, with a luminosity of about 10 000–100 000 times the Sun’s, and a diameter from 20 to several hundred times the Sun’s. Stars of at least 10 solar masses become supergiants when they swell up and leave the main sequence towards the end of their lives. They occupy a band at the top of the Hertzsprung–Russell diagram and are of luminosity class I; this can be subdivided into Ia, Iab, and Ib, from the most to the least luminous examples. Rigel and Betelgeuse are well-known supergiants.