Object Analysis

The Crescent Nebula (NGC 6888) is an emission nebula in the constellation Cygnus, about 5,000 light-years away. It is formed by the fast stellar wind from the Wolf-Rayet star WR 136 colliding with and energizing the slower moving wind ejected by the star when it became a red giant around 250,000 to 400,000 years ago.

The result of this collision is a shell and two shock waves, one moving outward and one moving inward. The inward moving shock wave heats the stellar wind to X-ray-emitting temperatures. The nebula spans about 25 light-years across.

Wolf-Rayet stars like WR 136 are massive, hot, and highly unstable, shedding mass at an incredible rate. Astronomers predict that WR 136 will likely undergo a supernova explosion within the next million years, obliterating the beautiful crescent shell it created.