Conceptual illustration showing a cloud of high-energy particles flowing behind the rapidly rotating Black Widow pulsar B1957+20 (white, left). The pulsar is also moving through the galaxy at a high speed which creates an outer bow shock wave visible to optical telescopes. The pressure behind this outer shock wave creates a second shock wave that sweeps the cloud of high-energy particles back from the pulsar to form the cocoon. The Black Widow pulsar is emitting intense high-energy radiation that appears to be destroying a companion star through evaporation. It is one of a class of extremely rapidly rotating, very old neutron stars called millisecond pulsars.