Original URL: http://www.theregister.co.uk/2007/01/10/four_magnetic_poles/

Scientists spot pulsar with 4 magnetic poles

Double bubble

By Lester Haines

Posted in Science, 10th January 2007 15:35 GMT

The 209th Meeting of the American Astronomical Society (AAS) in Seattle has been entertained by the news that the neutron star within the Crab Nebula may have twice the normal complement of magnetic poles, the BBC reports.

The nature of the star's radio pulse emissions leads the Arecibo Observatory in Puerto Rico to conclude that it possibly has four magnetic poles. Depending on a pulsar's orientation to Earth, its rotation and said emissions issuing forth from the poles will allow detection of one or two pulses. Where two are detected, as is the case in the Crab Nebula, the emissions from the north and south poles should be identical.

In the case of this particular neutron star, however, scientists detected a main pulse, occasionally producing "enormously strong pulses" dubbed "megapulses", and an "interpulse" which were "dramatically different in their profiles".

Tim Hankins, acting director of the Arecibo Observatory in Puerto Rico, explained: "We think we've got a much more complicated magnetic field than the simple dipole model. What we think is that there is another pole, possibly with a partner, that is influencing and distorting the magnetic field."

The four-pole theory is based on the fact that, although the team has spotted just one extra pole, it will likely have an opposite.

The Crab Nebula pulsar was created as a result of a supernova explosion on 4 July 1054 (AD). Professor Hankins pointed out that the explosion may have been "very asymmetric", adding: "Any models you see of supernova explosions are incredibly convoluted. It just doesn't go down as sphere and rebound as a nice sphere. The magnetic pole is frozen in so it gets all mixed up as well." ®