1. Department of Physics, School of Science, The University of Tokyo, 113-0033, Japan
2. Princeton University Observatory, Peyton Hall, Princeton, New Jersey 08544, USA
3. Department of Physics and Astronomy, Johns Hopkins University, 3701 San Martin Drive, Baltimore, Maryland 21218, USA
4. National Astronomical Observatory, 2-21-1 Osawa, Mitaka, Tokyo 181-8588, Japan
5. Department of Physics, University of California at Davis, 1 Shields Avenue, Davis, California 95616, USA
6. Institute of Geophysics and Planetary Physics, Lawrence Livermore National Laboratory, L-413, 7000 East Avenue, Livermore, California 94550, USA
7. Department of Astronomy and Astrophysics, University of Chicago, 5640 South Ellis Avenue, Chicago, Illinois 60637, USA
8. Fermi National Accelerator Laboratory, PO Box 500, Batavia, Illinois 60510, USA
9. Institut d'Estudis Espacials de Catalunya/CSIC, Gran Capita 2-4, 08034 Barcelona, Spain
10. Steward Observatory, University of Arizona, 933 North Cherry Avenue, Tucson, Arizona 85721, USA
11. Institute for Cosmic Ray Research, The University of Tokyo, 5-1-5 Kashiwa, Chiba 277-8582, Japan
12. Department of Physics, Carnegie Mellon University, Pittsburgh, Pennsylvania 15213, USA
13. Max-Planck Institute for Astronomy, Königstuhl 17, D-69117 Heidelberg, Germany
14. Apache Point Observatory, PO Box 59, Sunspot, New Mexico 88349, USA
15. Department of Physics, University of Michigan, 500 East University Avenue, Ann Arbor, Michigan 48109, USA
16. Department of Astronomy and Astrophysics, Pennsylvania State University, 525 Davey Laboratory, University Park, Pennsylvania 16802, USA
17. Enrico Fermi Institute, University of Chicago, 5640 South Ellis Avenue, Chicago, Illinois 60637, USA

Correspondence to: Naohisa Inada¹ Email: inada@utap.phys.s.u-tokyo.ac.jp

Abstract

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) predicts^{1, 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 searches^{8, 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 expectations^{3, 4, 5} based on the cold-dark-matter model.