Astronomers have compiled the largest, most detailed map of the Universe so far and believe that it shows beyond doubt the presence of an all-pervading "dark energy" throughout the cosmos. The three-dimensional map contains 200,000 galaxies and covers six per cent of the sky. The furthest galaxies in the map are two billion light years away. Such maps are invaluable because the large-scale structure of the Universe reveals the interplay of cosmic forces during the last 13 billion years. The new map comes from the Sloan Digital Sky Survey (SDSS), an international collaboration of over 200 astronomers at 13 institutes around the world. To build the map, astronomers first identified individual galaxies on wide-angle pictures taken by the SDSS's 2.5-metre telescope at Apache Point Observatory, New Mexico. Next, they used the telescope's special fibre optic system to record the spectra of up to 608 galaxies at a time, allowing them to calculate each galaxy's distance and fix its position within the 3D map. Until the mid-1990s most cosmologists believed that gravity, created by ordinary matter and invisible dark matter, sculpted the Universe. Then, exploding stars in deep space hinted that a cosmic force was driving the Universe apart. Astronomers dubbed this force dark energy. In February 2003, the merging of a large-scale galaxy map from the Anglo-Australian 2dF galaxy redshift survey with data on the afterglow of the Big Bang from NASA's WMAP spaceprobe showed strong evidence for dark energy. The new work - using different galaxies, instruments, personnel and analysis - provides the same result to better precision, and puts the existence of dark energy beyond doubt. One of the astronomers leading the project, Max Tegmark at the University of Pennsylvania, told New Scientist: "There is no longer any single data set to blame. The web of evidence is very strong and all observations are pointing to dark energy." Source: New Scientist