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SN1999em: A supernova detected in a spiral galaxy 25 million light years from Earth.
(Credit: X-ray: NASA/CXC/SAO, Optical: Palomar Observatory Digital Sky Survey)

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

CXC operated for NASA by the Smithsonian Astrophysical Observatory