Dark matter clues in galactic crash

From The Times
December 27, 2008


Dark matter in Galaxy cluster
Space Images of a spectacular intergalactic collision between galaxy clusters have provided new evidence for the existence of dark matter, which scientists believe forms an invisible framework for the Universe.

The pink in the picture above indicates ordinary matter - mostly hot gas - while the blue area is believed to indicate the presence of dark matter. As the two clusters merged at millions of miles per hour, the hot gas collided and slowed down, while the dark matter did not, explaining the wider spread of blue.

The collision happened halfway across the Universe about 100 million years ago. The image of the cluster, known as MACSJ0025.4-1222, was captured with the Nasa Chandra X-ray Observatory and the Hubble Space Telescope. source