Which star is classified as a Wolf Rayet star?

Wolf Rayet stars are a special class of massive stars characterized by their strong stellar winds and specific spectral lines, notably the emission lines of helium and heavier elements such as carbon and nitrogen. These stars are known for being in a late stage of stellar evolution, typically following the main sequence phase and often before ultimately exploding as supernovae.

NGC 6888, also known as the Crescent Nebula, is associated with a Wolf Rayet star — specifically WR 136. This star showcases the defining features of Wolf Rayet stars, including its strong emission lines and significant mass loss due to its intense stellar wind. The nebula itself is formed by the material ejected from the star, demonstrating the typical behavior of Wolf Rayet stars as they shed their outer layers.

The other choices do not possess the characteristics typical of Wolf Rayet stars. For instance, Cygnus X-1 is a well-known black hole system but not a Wolf Rayet star. Alpha Orionis, or Betelgeuse, is a red supergiant, whereas M1, or the Crab Nebula, is the remnant of a supernova, which does not classify as a Wolf Rayet star. Thus, NGC 6888 stands out as