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Under the Milky Way Series by ross berens
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.
Rosette Nebula in RGB & HA