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Mapping the large scale structure of dark matter
Posted: 10 January 2012

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A large scale map of the web of dark matter that weaves through the Universe has been unveiled at the American Astronomical Society meeting in Austin, Texas, as part of the Canada-France-Hawaii Telescope Lensing Survey (CFHTLenS).

The densest regions of the dark matter cosmic web host massive clusters of galaxies. Image: Van Waerbeke, Heymans, and CFHTLens collaboration.

The results, presented by Dr Catherine Heymans of the University of Edinburgh, Scotland, and Associate Professor Ludovic Van Waerbeke of the University of British Columbia, Vancouver, were derived from the analysis of ten million galaxies across four regions of the sky mapped by the 340-megapixel camera on the Canada-France-Hawaii Telescope in Hawaii.

The galaxies are located at a distance of six billion light years, meaning that their light has been traveling for roughly half the age of the Universe. The astronomers studied the way in which light from the galaxies bent as it passed massive clumps of dark matter, a technique known as gravitational lensing.

Less than four percent of our Universe is made up of regular matter like stars and planets, the rest is invisible, or 'dark' matter and energy. But astronomers can detect the presence of dark matter by studying its gravitational effect on galaxies, which is thought to 'stick' them together in a giant web. Indeed, the dense hubs of dark matter revealed by the new map correspond to the most massive clusters of galaxies.

The dark matter cosmic web is seen in all four directions surveyed by the Canada-France-Hawaii Telescope. From left to right: spring, summer, fall and winter. Image: Van Waerbeke, Heymans, and CFHTLens collaboration.

Although the team's results have long been predicted by computer simulations, this is the first direct glimpse at its large-scale prevalence across the Universe in all directions.

"It is fascinating to be able to 'see' the dark matter using space-time distortion," says Van Waerbeke. "It gives us privileged access to this mysterious mass in the Universe which cannot be observed otherwise. Knowing how dark matter is distributed is the very first step towards understanding its nature and how it fits within our current knowledge of physics."