The “Black Widow” pulsar is moving through the galaxy at a speed of almost a million kilometers per hour. A bow shock wave due to this motion is visible to optical telescopes, shown in this image as the greenish crescent shape. The pressure behind the bow shock creates a second shock wave that sweeps the cloud of high-energy particles back from the pulsar to form the cocoon.
The Whirlpool Galaxy, the red spiral, and its companion galaxy, NG 5195 are 23 million light-years from Earth. The warm dust in red is a sign of active star formation probably triggered by a collision between the two galaxies. (photo: NASA / JPL-CALTECH / R. KENNICUTT (UNIV. AZ))