'Giant cosmic car crash' offers fresh proof of existence of dark matter

Published on Friday 26 December 2008 20:34

FRESH evidence of the existence of dark matter has been discovered by astronomers studying a spectacular collision in space described as a "giant cosmic car crash".

New clues have been gleaned about the material that forms much of the universe from the blues and pinks detected after galaxy clusters smashed into each other.

Scientists believe dark matter, although invisible to the naked eye, provides a vital "scaffolding" for the universe, forming a framework for planets, stars and galaxies.

It is thought there is five times more dark matter than visible matter in the universe.

Experts believe that, as the universe was being formed after the Big Bang, the gravitational force of this huge quantity of dark matter formed planets and galaxies, shaping the cosmos.

The pink in the picture indicates ordinary matter – mostly hot gas – and the blue area is believed to show the presence of dark matter.

The cluster is made up of hundreds of galaxies, and is about half way across the universe – 5.7 billion light years away.

The two clusters that formed it were each one million billion times the weight of the sun.

Richard Massey, an astronomer at the Royal Observatory, in Edinburgh, who took part in the research, said life would not have come into being without dark matter, so any new clues were a step forward in investigating the make-up of the universe. He said the universe could not have formed "without the dark matter scaffolding being there in the first place".

"It is very important and crucial. Life wouldn't exist without this stuff," he said.

This image of the cluster, known as MACSJ0025.4-1222, was captured with Nasa's Chandra X-ray Observatory and the Hubble Space Telescope.

As the two clusters merged at millions of miles an hour, the picture indicates that the hot gas collided and slowed down, researchers said. But the dark matter did not, as shown by the wider spread of blue, they believe.

The separation of the pink and blue provides evidence for dark matter, and backs the view that particles of the matter react only very weakly with each other or not at all, apart from the pull of gravity.

Mr Massey added: "The unusual configuration of this cosmic collision enables astronomers to study mysterious, invisible dark matter."

The discovery backs evidence from an earlier image of colliding galaxies, known as the Bullet Cluster, which also showed evidence of a separation of dark and ordinary matter, two years ago.

The new results show the Bullet Cluster was not an exception and that the earlier results were not the product of an unknown error.

The latest study was carried out by an international team of astronomers, led by Marusa Bradac, of the University of California Santa Barbara, and Steve Allen, of the Kavli Institute for Particle Astrophysics and Cosmology at Stanford.

Other collaborators included Tommaso Treu, Harald Ebeling, R Glenn Morris, Anja von Linden and Douglas Applegate. Their results will appear in the Astrophysical Journal.