The large-scale structure of the Universe appears to be dominated by vast "hyperclusters" of galaxies, according to the Sloan Digital Sky Survey, compiled with a telescope at Apache Point, New Mexico. The 2011 survey plots the 2D positions of galaxies across a quarter of the sky. The science team concluded that it could mean that gravity or dark energy – or something completely unknown – is behaving very strangely.
We know that the universe was smooth just after its birth. Measurements of the cosmic microwave background radiation (CMB), the light emitted 370,000 light years after the big bang, reveal only very slight variations in density from place to place. Gravity then took hold and amplified these variations into today's galaxies and galaxy clusters, which in turn are arranged into big strings and knots called superclusters, with relatively empty voids in between.
On even larger scales, though, cosmological models say that the expansion of the universe should trump the clumping effect of gravity. That means there should be very little structure on scales larger than a few hundred million light years across. "Should be." But according to Shaun Thomas of University College London (UCL), and colleagues aggregations of galaxies stretching for more than 3 billion light years have been found. The hyperclusters are not very sharply defined, with only a couple of per cent variation in density from place to place, but even that density contrast is twice what the tandard cosmological modelstheory predict.
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