15 Apr. 2011

 

Giant stars uncovered in X-rays

 

Thanks to the X-ray space telescope Chandra, some extremely massive stars have been identified within the Galactic plane, and may be members of a large population of such stars hidden by the obscuring medium that characterises these regions of the Milky Way.
Four stars have been detected, with masses of at least 25 solar masses, at distances between 7,500 and 18,000 light years. Their very large masses means that they must be very young, only a few million years old, or else they would have already ended their lives as supernovae.
Of course, these stars also emit much longer wavelength radiation, and in fact the Spitzer space telescope, sensitive to infrared wavelengths, also detects them. In the above image, taken by Spitzer, two of the stars detected by Chandra are shown in artificially darkened regions of the image. But in the infrared, although to a lesser extent than in the optical, the dust obscuration towards the infrared sources did not permit them to be identified as massive stars.
The fact that they are detected in X-rays, however, helps to characterise the environment in which they are embedded and the nature of the sources. Because such massive stars produce incredibly strong stellar winds that radiate out from the star at speeds of 3 million km/h, if they also have a nearby companion with its own stellar wind, then the shock produced where the two winds meet is so violent that it generates temperatures of 100 million degrees, sufficient to produce strong X-ray emission.
The task of Chandra, and also its companion X-ray telescope XMM-Newton, is to determine the nature of the more than 100 X-ray sources detected by previous X-ray missions, whose identity remains unknown.

 

by Michele Ferrara & Marcel Clemens

credit: X-ray: NASA/University of Sydney/G.Anderson et al;
IR: NASA/JPL-Caltech