This visible-light image from the Sloan Digital Sky Survey shows spiral galaxy NGC 7331, center, where astronomers observed the unusual supernova SN 2014C .

The inset images are from NASA's Chandra X-ray Observatory, showing a small region of the galaxy before the supernova explosion (left) and after it (right). Red, green and blue colors are used for low, medium and high-energy X-rays, respectively.