Wolf-Rayet star. Computer illustration of a nebula around a Wolf-Rayet (WR) star. WR stars are rare and extremely hot stars which continuously eject hot gas from their surfaces. This hot gas is ionised by radiation from the star, causing it to glow. The ejection of the gas, primarily hydrogen, exposes the inner parts of the star, composed of the products of the nuclear reactions which power it. The spectrum of a WR star reveals its composition, either helium and nitrogen (WN stars), or helium, carbon and oxygen (WC stars). WR stars may be a million times more luminous than the Sun, and lose mass up to 100 times more rapidly than comparably luminous stars.