A magnetic field in a Herbig star

Young Herbig stars do not have the correct internal conditions to generate an appreciable magnetic field. Yet for twenty years, astronomers have been detecting X-ray emission from them. Using XMM-Newton to observe AB Aurigae, astronomers have found that the X-rays were coming from high above the star. X-rays high above the surface means that gas given off by the star, called the stellar wind, from two different hemispheres is probably being guided together into a collision. And the only thing that could do that was a magnetic field. The explanation could be that, as the vast pocket of gas collapsed to become AB Aurigae, it pulled with it part of the magnetic field that threaded that region of space. This field is now trapped inside the star and funnels the stellar winds together. Winds from the two hemispheres thus collide to create the X-rays. It is a neat explanation for a twenty-year mystery but, at the moment, nobody knows whether this is applicable to other Herbig stars.