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A Wolf-Rayet star (WR star) is a hot star with broad helium emission lines, suggesting Doppler broadening due to a high velocity stellar wind. They are massive, initially above 20 solar masses, very hot, at 30,000K to 200,000K, and very luminous, at 10,000 to millions of times the Sun's bolometric luminosity, though most of the luminosity is in ultraviolet and X-rays. A Wolf-Rayet star is considered one of the final stages of the life of a massive star. More than 200 Wolf-Rayet stars have been identified in the Milky Way, the first having been noticed in 1867 in the constellation Cygnus.