Crescent Nebula

Located near Sadr, the star at the heart of the celestial swan, the Crescent Nebula gains its radiance from a Wolf-Rayet star. Called WR 136, and just 4-5 million years old, this immense star has quickly burned through its store of fuel and now ejects mass from its outer layer at a rate of nearly one full solar mass every 10,000 years. This fast-moving hot gas, which moves at a speed of 2,000-3,000 km/s, collides with cooler gas ejected by the star during its younger and quieter days, and the collision excites the scant hydrogen and oxygen gas to radiate light. Massive and mass-losing Wolf-Rayet stars such as WR 136 are rare: there are only about 150 such stars known in the Milky Way.