Chandra Release - August 27, 2008

Visual Description: MACS J0025.4-1222

This Chandra and Hubble image shows massive galaxy clusters that underwent a powerful collision. At the center of the field is a large hot pink glob, which is surrounded on its left and right by a large blue blob, all of it dripping in small golden galaxies and white foreground stars, on a black background.  Known as MACS J0025.4-1222, the image shows a clear separation between dark and ordinary matter. This helps answer a crucial question about whether dark matter interacts with itself in ways other than via gravitational forces. Using optical images from Hubble, we can infer the distribution of the total mass (colored in blue) -- dark and ordinary matter -- using a technique known as gravitational lensing. The Chandra X-ray Observatory data enabled the astronomers to accurately map the position of the ordinary matter, mostly in the form of hot gas, which glows brightly in X-rays (pink.)  As the two clusters that formed MACS J0025 merged at speeds of millions of miles per hour, the hot gas in each cluster collided with the hot gas in the other and slowed down, but the dark matter did not. The separation between the material shown in pink and blue therefore provides direct evidence for dark matter and supports the view that dark matter particles interact with each other only very weakly or not at all, apart from the pull of gravity.