SN1999em: A supernova detected in a spiral galaxy 25 million light years from Earth.
Caption: In late October of 1999, a supernova was detected in NGC 1637, a spiral galaxy that is 25 million light years from Earth. Chandra observed the supernova twice soon after the explosion. X rays, shown by contours overlaid on an optical mage, were detected from 3 million degree gas produced by the supernova. An X-ray source in the center of the galaxy was also detected.
Scale: Image is 2 arcmin on a side.
Chandra X-ray Observatory ACIS Image