Cassiopeia A Supernova Explosion, artist’s impression

A supernova such as the one that resulted in Cas A is the explosive demise of a massive star that collapses under the weight of its own gravity. The collapsed star then blows its outer layers into space in an explosion that can briefly outshine its entire parent galaxy. Credit: ESA/Hubble (M. Kornmesser L. L. Christensen)