Space Telescope Science Institute
A team of scientists studying the galaxy cluster Abell 2744, nicknamed Pandora's Cluster, have pieced together the cluster's complex and violent history using telescopes in space and on the ground, including the Hubble Space Telescope, the European Southern Observatory's Very Large Telescope, the Japanese Subaru telescope, and NASA's Chandra X-ray Observatory.
The giant galaxy cluster appears to be the result of a simultaneous pile-up of at least four separate, smaller galaxy clusters that took place over a span of 350 million years. The galaxies in the cluster make up less than five percent of its mass. The gas (around 20 percent) is so hot that it shines only in X-rays (colored red in this image). The image is a composite of separate exposures made by Hubble Space Telescope Advanced Camera for Surveys detectors in October 2009, the VLT, and the Chandra ACIS detector. Hubble provides the central, most detailed part of the image, while the VLT, which has a wider field of view, provides the outer parts of the image. The distribution of invisible dark matter (making up around 75 percent of the cluster's mass) is colored here in blue.