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Detection of weak gravitational lensing distortions of distant galaxies by cosmic dark matter at large scales


Most of the matter in the Universe is not luminous, and can be observed only through its gravitational influence on the appearance of luminous matter. Weak gravitational lensing is a technique that uses the distortions of the images of distant galaxies as a tracer of dark matter: such distortions are induced as the light passes through large-scale distributions of dark matter in the foreground. The patterns of the induced distortions reflect the density of mass along the line of sight and its distribution, and the resulting ‘cosmic shear’ can be used to distinguish between alternative cosmologies. But previous attempts to measure this effect have been inconclusive. Here we report the detection of cosmic shear on angular scales of up to half a degree using 145,000 galaxies and along three separate lines of sight. We find that the dark matter is distributed in a manner consistent with either an open universe, or a flat universe that is dominated by a cosmological constant. Our results are inconsistent with the standard cold-dark-matter model.

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Figure 1: The distorted universe.
Figure 2: Making stars round.
Figure 3: Lens-induced galaxy orientation correlations.
Figure 4: Detection of ellipticity correlations.
Figure 5: Comparison of ellipticity correlations with predictions.


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We thank W. Hu and J. Miralda-Escudé for help with theoretical predictions of several cosmological models. We also thank S. Gentile for artwork, and the staff of CTIO for their help with the BTC project and for their upgrading and maintenance of the delivered image quality of the Blanco telescope. Cerro Tololo Inter-American Observatory is a division of National Optical Astronomy Observatory (NOAO), which is operated by the Association of Universities for Research in Astronomy, Inc., under cooperative agreement with the NSF. Big Throughput Camera construction was partially supported by the US National Science Foundation.

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Wittman, D., Tyson, J., Kirkman, D. et al. Detection of weak gravitational lensing distortions of distant galaxies by cosmic dark matter at large scales. Nature 405, 143–148 (2000).

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