Light shed on dark matter
2008-08-28 11:34
Washington - Space telescopes have captured images of a mammoth collision between two galaxy clusters that have shed some light into the universe's mysterious dark matter, Nasa said.
The images taken by the Hubble Space Telescope and Chandra X-ray Observatory show a clear separation between dark and ordinary matter during the clash 5.7 billion light years from Earth, the US space agency said on Wednesday.
The astronomers were able to differentiate between the two substances with a technique known as gravitational lensing in which dark matter appears in blue in the image while ordinary matter, which is mostly in the form of hot gas, looks pink.
As the two clusters merged at speeds of millions of miles per hour, the hot gas in each cluster collided and slowed down, the astronomers said. The dark matter, however, did not.
Mysterious
The separation between the pink and blue material provides direct evidence for dark matter and supports its particles interact with each other only very weakly or not all, apart from the pull of gravity, the astronomers said.
"It is in our view an important step forward to understanding the properties of the mysterious dark matter," said Marusa Bradac, a University of California, Santa Barbara researchers who leads the team that captured the collision.
"Dark matter makes up five times more matter in the universe than ordinary matter. This study confirms that we are dealing with a very different kind of matter, unlike anything that we are made of," he said.
"And were are able to study it in a very powerful collision of two clusters of galaxies."
The discovery independently confirms the findings in 2006 of another collision known as the Bullet Cluster, which also showed a clear separation between dark and ordinary matter.
Around a fifth of the Universe is believed to consist of dark matter, spreading out in mysterious filaments, sheets and clusters.
But, with present technology, it cannot be seen directly. Its existence is perceived indirectly, through the gravitational pull it exerts on light.