XMM-Newton unlocks magnetic mystery

Stephen Withers
Friday, 23 February 2007 05:04

Science - Space

Observations using the ESA's XMM-Newton X-ray observatory have allowed scientists to propose an answer to a twenty year old puzzle.

Herbig stars - large stars emitting X-rays even though our understanding of their structure suggests they shouldn't - have been known for a couple of decades. One theory was that the X-rays come from companion stars in orbit around them.

Data collected by XMM-Newton has allowed an international team led by Manuel Güdel and Alessandra Telleschi of the Paul Scherrer Institut in Switzerland to suggest a neater solution.

Observations of AB Aurigae, a Herbig star in the Taurus-Auriga cloud - showed that its X-ray emissions have the same periodicity as the optical and ultraviolet light coming from it. "Finding the same periodicity confirms that the X-rays are coming from AB Aurigae and not from a companion star," says Güdel.

The data also showed that the gas emitting the X-rays was much cooler than expected.

An important clue came from XMM-Newton's spectrometer, which showed the X-rays were coming from high above the star. Güdel, Telleschi and the team suggest that a magnetic field within the star funnels its stellar winds together, and the resulting collisions create the X-rays.

The next job is to study other Herbig stars to see if this model also fits them.