Crab Nebula Variability

The Crab Nebula is the result of a supernova that exploded in Earth's skies in 1054. Chinese astronomers recorded the event while Europe was in the Dark Ages. Through the twentieth century, the Crab was seen as an extremely stable energy source, to the extent that it has been used to calibrate instruments aboard space probes.

Now, some space-based X-ray telescopes have found the Crab to be more variable than expected in that region. A dip in output in the low frequency part of the X-ray spectrum, as well as variability in the high frequency area, seems to be based in the central part of the Nebula, about a light year across. Within that part lies the rapidly spinning neutron star which is the remains of the original star plus powerful magnetic fields associated with that star.

Astronomers think the variability is connected to the magnetic fields. They will go back over previous studies to determine whether the unrecognized variability in the Crab may have affected the results of those studies.