http://netvouz.com/pdboyer/tag/invisible?feed=rss pdboyer's bookmarks tagged "invisible" on Netvouz http://chandra.harvard.edu/photo/2004/darkenergy/ A galaxy cluster is comprised on hundreds of galaxies embedded in a cloud of extremely hot gas and dark matter. Dark matter, an invisible and unknown type of material, is postulated to hold clusters together. X-ray observations have the unique ability to determine the ratio of the mass of the hot gas and the mass of the dark matter in a cluster. The observed values of the gas fraction depend on the assumed distance to the cluster. pdboyer Sat, 06 Nov 2010 19:41:34 GMT