Pulsars (2) ...

In visible light, the Crab Pulsar appears to be a magnitude 16 star near the center of the nebula, but stroboscopic techniques show it to be pulsing. The following figure shows the Crab Pulsar in action at visible wavelengths. In this composite of European Southern Observatory data, the pulsar is shown in a time lapse image at the top and the light curve is displayed at the bottom on the same timescale.

The image sequence is a composite of images taken through three different filters, all in the visible part of the spectrum. Both the image sequence and the light curve show clearly the "double pulsing" of the Crab: in each cycle there is a strong primary pulse followed by a much weaker secondary pulse. The period (time between successive primary or secondary pulses) implies that the pulsar is emitting one primary and one secondary pulse about 30 times every second.