Cygnus Loop supernova blast wave, 1993.

This is an image of a small portion of the Cygnus Loop supernova remnant, which marks the edge of a bubble-like expanding blast wave from a colosal stellar explosion, occurring about 15,000 years ago. The HST image shows the structure behind the shock waves, allowing astronomers for the first time to directly compare the actual structure of the shock with theoretical model calculations. Next to the supernova remnants, these shock models are important in understanding a wide range of astrophysical phenomena, from winds in newly-formed stars to cataclysmic stellar outbursts.