Galaxy NGC 2403: Before and After Supernova 2004dj Outburst

The image at left represents a small region of NGC 2403, a galaxy located 11 million light-years from Earth. The photo was taken two months before a massive star exploded. The image pinpoints the location of the stellar blast, known as supernova 2004dj, within a cluster of massive, generally blue (but some red) stars called Sandage 96. The cluster's total mass is estimated at about 24,000 times the mass of the Sun. The stars in this cluster are so far away that their light blends together, appearing as the light of a single star. The yellow object below and to the left of the cluster is a foreground star in our Milky Way Galaxy. The pink blob at bottom, center is a star-birth region. This image was taken May 8, 2004, with the WIYN 0.9-meter mosaic camera at Kitt Peak National Observatory in Arizona.

The image at right pinpoints the supernova blast. The photo was taken on Aug. 17, 2004, with the Hubble Space Telescope's Advanced Camera for Surveys. The light from this outburst outshines every star in the massive cluster. Similar blue clusters of stars can be seen throughout the image. The bluish-pink blob towards the bottom of the image is a large star-birth region.