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In a map of dark matter, clues to galaxies' histories

Researchers unveil 3-D view of a part of 'unseen' universe.

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The map of the universe, which astronomers have been plotting for some 20 years, reveals that the vast numbers of visible galaxies are not randomly arrayed, but rather display a breathtaking structure. Now scientists are detecting structure in the universe's unseen "dark matter" – whose gravity herds stars into galaxies and galaxies into enormous clusters tens of millions of light-years across.

Sunday, a team of astronomers unfolded the first large-scale map of dark matter, one of the cosmos's most enigmatic ingredients. Such maps are vital to understanding how galaxies evolved and gathered themselves into larger structures, researchers say.

To the untrained eye, the map looks a bit like a hiker's topographic map. But to astrophysicists, the 3-D map – which represents a time span dating back to roughly half the age of the universe – is independent evidence confirming their thesis of how the cosmos evolved after the big bang some 13.6 billion years ago.

Filaments of dark matter grow as time passes, the map indicates. Galaxies form within the filaments. Where filaments cross and join, larger amounts of dark matter accumulate – corresponding to galaxy clusters astronomers can see.

A bigger span of sky

The results represent "an exciting new view of the dark universe," according to Eric Linder, an astrophysicist at the Lawrence Berkeley National Laboratory, in Berkeley, Calif. "Most attempts at detecting dark matter have involved a single galaxy or cluster of galaxies," he says. The new map "scans a much wider area of the universe" – a patch roughly equivalent to an area that would be covered by eight full moons corralled into a single part of the sky, as seen from Earth.

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