Wolf-Rayet nebula NGC 2359, optical image. This nebula, lying around 40,000 light years from Earth in the constellation Canis Major, is sometimes known as Thor's Helmet. A Wolf-Rayet nebula is formed by the ejection of glowing, ionised gas from a hot, central star. These Wolf-Rayet stars lose mass 100 times faster than stars of comparible luminosity and may be a million times more luminous than the Sun. The interaction of the ejected gas with interstellar matter forms a bubble around the star, which glows when ionised by the star's radiation.