This image provided by NASA's Chandra X-ray Observatory Tuesday Dec. 16, 2008 shows the galaxy cluster Abell 85, located about 740 million light years from Earth. The purple emission is multi-million degree gas detected in X-rays by NASA's Chandra X-ray Observatory. This galaxy cluster is one of 86 observed by Chandra to trace how dark energy has stifled the growth of these massive structures over the last 7 billion years. Galaxy clusters are the largest collapsed objects in the Universe and are ideal for studying the properties of dark energy, the mysterious form of repulsive gravity that is driving the accelerated expansion of the Universe.
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