X-ray/optical image of Westerlund 1
Credit: NASA/CXC/UCLA/M.Muno et al.

Missing Holes

The star cluster Westerlund 1 is a dense group of very massive stars packed closely together, and is by far the most massive cluster in the Milky Way. Sharing such close quarters, astronomers believe that collisions between compact remnants of dead stars would eventually produce large numbers of black holes. Perhaps clusters like Westerlund 1 might be a nursery for so-called intermediate mass black holes, those objects with masses much greater than stellar mass black holes (i.e. a few solar masses) but much less than the "supermassive" black holes (i.e. millions of solar masses). Surprisingly, though, studies of Westerlund 1 by the Chandra X-ray Observatory show the presence of neutron stars, but no clear evidence for the presence of black holes in the cluster. The image above left shows an optical image of the cluster, while the image on the right is a Chandra X-ray image of the cluster. The arrow on the X-ray image shows the location of a neutron star in the cluster. But where are the black holes?

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Page Author: Dr. Michael F. Corcoran
Last modified Friday, 20-Apr-2012 15:20:51 EDT