The American astronomers have found the first space body with more than two poles.

The pulsating star inside the Crab Nebula, in the constellation of Taurus, is believed to possess up to four magnetic poles.

Neutron stars are the dense remains of massive stars that ended in supernova explosions. Some are called pulsars (pulsating stars), because they emit lighthouse-like beams of radio waves, and the magnetic field that drives their emission is highly unusual. "If the findings were confirmed, the neutron star would be the first cosmic object found to have four poles," said Professor Tim Hankins, from the Arecibo Observatory in Puerto Rico and lead investigator on the study.

In a two-pole neutron star, either one or two pulses will be detected and the pulsar of Crab Nebula is one of those for which two pulses can be identified. The main pulse produces occasionally enormously strong pulses called "megapulses", while the other beam is called the interpulse. "The profiles of pulses from the north and south poles of a neutron star should be identical," said Hankins.

But the astronomers discovered for the first time in a pulsar that the two pulses were very different in their profiles. "We think we've got a much more complicated magnetic field than the simple dipole model," said Hankins. "What we think is that there is another pole, possibly with a partner, that is influencing and distorting the magnetic field," he continued.

As magnetic poles always come in pairs, a fourth one must be there. The four-poled star emerged after a supernova explosion that was seen on Earth on 4 July, AD 1054. "The magnetic poles were essentially "frozen" into the remnant after the supernova explosion." said Hankins. Supernova explosions are believed to be very asymmetric. "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."

Image credit: NASA-MSFC