It’s one of the universe’s most enduring mysteries — what comprises the “dark matter” that scientists believe most of the universe is made of, but which humans have been unable yet to see? Scientists using the Chandra X-ray Observatory were able to precisely determine the distribution of dark matter in a distant galaxy cluster named EMSS 1358+6245. Astronomers have long believed that most of the matter in the universe is in some dark, as yet undetected, form that makes its presence felt only through gravity. “The new Chandra observations are providing new clues about the nature of this mysterious stuff,” said Mark Bautz of the Massachusetts Institute of Technology, one of the scientists who obtained the results. In the cluster EMSS 1358+6245, the mass of the dark matter was found to be about four times that of the “normal” matter, which is matter not comprised of exotic particles.