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Sky surveys mapping dark and ordinary matter
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Sky surveys: mapping dark and ordinary matter

January 25, 2013
Since the mid-1930's astronomers have postulated the existence of dark matter – a hypothetical matter that cannot be detected by its emitted radiation but only inferred by its gravitational effect on normal (baryonic) matter. Mapping the distribution of dark matter in space and time is fundamental to understanding how galaxies grew and clustered over billions of years. Tracing the growth of clustering in the dark matter may also eventually shed light on dark energy, a force which repels matter rather than attracts it as gravity does. In the popular concordance model of the Universe normal matter accounts for 5%, dark matter 25% and the remaining 70% is attributed to dark energy. This image is the first large-scale map of the dark matter and baryon distributions in the universe. The distribution of normal matter (in red) was determined mainly by XMM-Newton, dark matter (in blue) and stars and galaxies (in grey) were observed in the optical band with the Hubble telescope. All the baryons observed by XMM-Newton are located within dark matter clumps and filaments. This means that normal matter, mostly in the form of galaxies, accumulates along the densest concentrations of dark matter and that the galaxies and clusters of galaxies are assembled inside a dark matter scaffolding. This map is an important cosmological result and it confirms conventional theories where the filamentary structure of the Universe was formed under the pull of gravity. Copyright: NASA, ESA and R. Massey (California Institute of Technology)