Astronomy: Unexpected pulsations from a massive star

The discovery of pulsating X-rays, emanating from a massive non-degenerate star, is reported in Nature Communications this week. This type of star has not been seen to emit such pulsations and this discovery poses questions about our understanding of stellar winds, their X-ray emissions and their magnetism.

Intense radiation from massive stars drives fast stellar winds where shocks can develop, and it is commonly assumed that X-rays emerge from the shock-heated plasma. Degenerate, or compact, stars-such as neutron stars or white dwarfs-are known to exhibit pulsations in their X-ray emissions and some larger, non-degenerate stars (eight or more times the mass of our Sun) are known to show regular pulsations in other properties. However, it was neither theoretically predicted nor observed that X-ray emissions would also display pulsations.

Lidia Oskinova and colleagues now report the discovery of pulsating X-ray emissions from the non-degenerate, massive B-type star, Xi1 Canis Majoris. Using observations from the XMM-Newton telescope, the researchers found that this star displays oscillations in its X-ray output that coincide with the star’s fundamental oscillations.

At present, a detailed and conclusive understanding of the X-ray pulsations from Xi1 Canis Majoris is elusive, but the finding challenges the current physical picture of the behaviour of stellar winds from magnetic stars. The authors suggest that these pulsations may be caused by the heating and cooling of the solar plasma.