ASTRONOMERS have measured the precise distance to over a quarter of a million galaxies to gain new insights into a key period in cosmic history. The 3D map of the sky allows scientists to probe the time six billion years ago when dark energy became the dominant influence on the Universe’s expansion.

No-one knows the true nature of this repulsive force, but the exquisite data in the international BOSS survey will help test various theories.

“This is an incredibly exciting time to be working in cosmology, and we’re all privileged to be part of the Baryon Oscillation Spectroscopic Survey (BOSS),” said Prof Will Percival from the University of Portsmouth - a UK member of the international research group.

“What we’ve done is measure the 3D positions for just over 250,000 galaxies, covering the largest volume of the Universe ever surveyed. That gives us an amazing map that we can then analyze to try to understand how and why the Universe’s expansion is accelerating,” he told BBC News. The discovery that everything in the cosmos is moving apart at a faster and faster rate was one of the major breakthroughs of the 20th Century. It went against all preconceptions. Up until the discovery, it was thought the Universe’s expansion would most likely have been decelerating under the influence of gravity. Scientists now find themselves grasping for new physics to try to explain what is going on. One concerns so-called baryon acoustic oscillations. These are pressure-driven waves that passed through the very early Universe and which were imprinted on the distribution of matter once conditions had cooled below a certain point.                         –TT