The Source of Stelar Magnetism

The magnetic clouds

By Stefan Anitei on February 26th, 2007 11:21 GMT
One of the strangest recent space discoveries is provided by the star named AB Aurigae, situated about 460 light-years away: a strong magnetic field generated from a star that theoretically could not have produced it, according to current theories.

Till now, it was believed that strong magnetic fields are generated only by hot, young huge stars or from the powerful interaction between two neighboring stars in a binary system.

But AB Aurigae does not match any of these situations. The star is too small (2.7 times bigger than Sun) and cool for the first condition.

But a team led by Manuel Guedel of the Paul Scherrer Institute in Villigen, Switzerland, employing the European Space Agency's orbiting XMM-Newton x-ray observatory, discovered that all AB Aurigae's radiations (x-ray, optical, and ultraviolet) changed in intensity in the same 42-hour cycle pattern, thus the star itself was the source of its magnetism. "Further observations and analysis revealed that AB Aurigae's x-rays are emanating from high above its surface," said Guedel.

That means that the solar winds in both of the star's hemispheres are moved by magnetic lines of force, generating x-rays. Trying to solve the puzzle of the magnetism's source, the team looked on an unlikely source: fossil magnetic fields, which develop within stellar-forming clouds.

They enter the composition of new stars, adding new power to the preexisting fields. "We cannot prove that this is what happened [with AB Aurigae], but no other explanation from stellar dynamic theory makes sense. Now astronomers can take a close look at other similar stars--called Herbig stars--to see whether their x-rays are being generated by fossil magnetic fields as well", said Guedel.

"If confirmed, the findings would be an important illustration of how a young star can interact with the surrounding material in a stellar nursery, in terms of latching onto a fossil magnetic field," said astrophysicist Rachel Osten of NASA's Goddard Space Flight Center in Greenbelt, Maryland.

"No one knows whether the other Herbig stars are generating x-rays from interactions with as-yet-hidden binary companions, but AB Aurigae does not appear to have a companion. And whatever the source, we know these stars can't generate magnetic fields on their own", added Osten.

Image credit: LA3B