Wolf-Rayet star. Artwork of a Wolf-Rayet star, a type of star that is a stage in the evolution of massive stars with a mass many times that of the Sun. These massive stars are also known as blue giant stars, as they emit strongly in the blue region of the spectrum. They are very hot stars, emitting large amounts of radiation and having a very strong stellar wind. This radiation and stellar wind blasts the star's atmosphere into space, forming an expanding nebula of material (purple) around the star. Possible stages after the Wolf-Rayet phase can include collapsars, black holes, and gamma ray bursts.