Figure 20-26: The Crab Pulsar (a) A pulsar is located at the center of the Crab Nebula, which is about 2000 pc (6500 ly) from Earth and about 3 pc (10 ly) across. The boxed area is shown in close-up in part (b). (b) We see a flash of visible light when the rotating pulsar’s beam is directed toward us (the “on” state). The pulsar fades (the “off” state) when the beam is aimed elsewhere. (c) The Crab pulsar also pulses “on” and “off” at X-ray wavelengths. The radio pulses, visual flashes, and X-ray flashes all have a period of 0.033 s.

(a, b: The FORS Team, VLT, European Southern Observatory; c: Harvard-Smithsonian Center for Astrophysics)