Cas-A supernova remnant. Coloured radio image of the Cassiopeia-A (Cas-A) supernova remnant. The colours represent observed intensity, from red (brightest) to dark blue (faintest) with a black background. Black lines have been added to show the orientation of Cas-A's magnetic field, which points radially outwards in a manner typical of recent supernovae. Cas-A is about 9000 light years away, and was created about 300 years ago when a star with a mass 20 times that of our Sun underwent a Type II supernova explosion. Image taken at a wavelength of 9 millimetres by the Effelsberg 100-metre telescope, Germany.