Chandra Release - November 2, 2005

Visual Description: Westerlund 1

The 2-panel image features a dense cluster of young stars called Westerlund 1 in an optical image on the left and a complementary X-ray image on the right. The main colors present in the image are blue and orange, with the blue color dominating the X-ray side of the image and the orange color dominating the optical side. The shape of the image is slightly crescent shaped though irregular, with many stars visible in both the blue and orange regions, scattered like bright jewels thrown across a shiny black table.  In the center of the Chandra X-ray Observatory image, there is a bright spot that stands out from the surrounding stars. The ESO optical image of Westerlund 1 shows a dense cluster of young stars, several with masses of about 40 suns. Some astronomers speculated that repeated collisions between such massive stars in the cluster might have led to formation of an intermediate-mass black hole, more massive than 100 suns. A search of the cluster with Chandra  found no evidence for this type of black hole. Instead they found a neutron star, a discovery which may severely limit the range of stellar masses that lead to the formation of stellar black holes. The neutron star is pointed out by an arrow at the bottom left tip of the irregular crescent shape in the X-ray.