Gravitational lensing is a powerful tool for the study of the distribution of dark matter in the Universe. The cold-dark-matter model of the formation of large-scale structures (that is, clusters of galaxies and even larger assemblies) predicts1,2,3,4,5,6 the existence of quasars gravitationally lensed by concentrations of dark matter7 so massive that the quasar images would be split by over 7 arcsec. Numerous searches8,9,10,11 for large-separation lensed quasars have, however, been unsuccessful. All of the roughly 70 lensed quasars known12, including the first lensed quasar discovered13, have smaller separations that can be explained in terms of galaxy-scale concentrations of baryonic matter. Although gravitationally lensed galaxies14 with large separations are known, quasars are more useful cosmological probes because of the simplicity of the resulting lens systems. Here we report the discovery of a lensed quasar, SDSS J1004 + 4112, which has a maximum separation between the components of 14.62 arcsec. Such a large separation means that the lensing object must be dominated by dark matter. Our results are fully consistent with theoretical expectations3,4,5 based on the cold-dark-matter model.
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Funding for the creation and distribution of the SDSS Archive has been provided by the Alfred P. Sloan Foundation, the Participating Institutions, the National Aeronautics and Space Administration, the National Science Foundation, the US Department of Energy, the Japanese Monbukagakusho, and the Max Planck Society. The SDSS website is http://www.sdss.org/. The SDSS is managed by the Astrophysical Research Consortium (ARC) for the Participating Institutions. The Participating Institutions are The University of Chicago, Fermilab, the Institute for Advanced Study, The Japan Participation Group, The Johns Hopkins University, Los Alamos National Laboratory, the Max-Planck-Institute for Astronomy (MPIA), the Max-Planck-Institute for Astrophysics (MPA), New Mexico State University, University of Pittsburgh, Princeton University, the United States Naval Observatory, and the University of Washington. This Letter is based in part on data collected at the Subaru telescope, which is operated by the National Astronomical Observatory of Japan, W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California, and the National Aeronautics and Space Administration, and the Apache Point Observatory (APO) 3.5-m telescope, which is owned and operated by the Astrophysical Research Consortium. Part of this work was performed under the auspices of the U.S. Department of Energy at the University of California Lawrence Livermore National Laboratory.
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