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Monster galactic cluster seen in deep Universe: European agency
2008-08-25
PARIS (AFP) - An orbiting observatory has spotted a massive cluster of galaxies in deep space that can only be explained by the exotic phenomenon known as dark energy, the European Space Agency (ESA) said on Monday. Spotted in a scan by ESA's orbiting X-ray telescope XMM-Newton, the cluster's mass is about 1,000 times that of our own galaxy, the Milky Way, it said. The huge cluster, known by its catalogue number of 2XMM J083026+524133, lies 7.7 billion light years from Earth and helps confirm the existence of dark energy, the agency said. Under this hypothesis, most of the Universe comprises "dark energy", an enigmatic force that is causing the expansion of the cosmos to accelerate. The outward drive of dark energy is such that, in more recent times, massive galaxy clusters have lacked the gravitational glue to be able to form. So the newly-discovered super-cluster can only have been formed earlier in the history of the Universe, a notion that is backed by its huge distance from Earth. "The galaxy cluster is so big that there can only be a handful of them at that distance," said ESA, likening the achievement to finding a "cosmic needle in a haystack." The observation was made by a team led by Georg Lamer of the Potsdam Astrophysics Institute, eastern Germany, initially using a photon imaging camera aboard the XMM-Newton. Intrigued by the indicators of scorching gases spewed out by X-ray sources, the astronomers followed up by getting a deep exposure image of the region from a large binocular telescope in the Arizona desert. "Dark energy" is believed to comprise more than 72 percent of the detected Universe and "dark matter" -- heavy particles still waiting to be discovered -- accounts for around 23 percent, according to cosmological theory. That leaves less than five percent of normal, or baryonic, matter, the category for the protons and neutrons that compose it.
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