Outbursts of a massive star created the gaseous shell known as the Crescent nebula. Rushing toward a supernova death, the star (not shown) had expanded enormously, jettisoning its outer layers at some 32,000 kilometers per hour. Radiation from the exposed inner layers then began ejecting gas at more than 100 times that speed.
The collision between the fast and slow winds formed the nebula, a portion of which appears here, and created two shock waves. One wave moved outward to produce the filamentary structure that appears green in visible light, and the other moved inward, producing a bubble of hot, X-ray-emitting gas (blue). Red blotches denote visible-light emission. This composite image was released last week by the Chandra X-ray Observatory Center in Cambridge, Mass.