Relativity Lite

Figure 11. A collision of galaxy clusters, MACSJ0025.4-1222, captured with the Hubble Space Telescope and NASA’s Chandra X-ray Observatory, provides striking evidence for dark matter and insight into its properties. The pink area is the normal matter from the collision of two galaxy clusters, heated up in the process of stopping much of each other’s forward momentum and therefore emitting X-rays captured by Chandra. The blue portions of this image map the mass required to account for gravitational lensing of light Hubble recorded from the distant objects by the cluster’s matter (dark and ordinary). The blue lobes on either side must therefore consist of dark matter that passed through the pink collision region with little to no interaction with the conventional matter nor with the oncoming dark matter from the other galaxy cluster. Credit: X-ray (NASA / CXC / Stanford / S. Allen); Optical/Lensing (NASA / STScI / UC Santa Barbara / M. Bradac) * * NASA Science Team, “A Clash of Clusters Provides Another Clue to Dark Matter,” National Aeronautics and Space Administration, August 27, 2008, https://​www​.nasa​.gov/​mission​_pages/​chandra/​multimedia/​photos08​-111​.html. See also the Bullet Cluster: “1E 0657-56: NASA Finds Direct Proof of Dark Matter,” National Aeronautics and Space Admin- istration, last modified August 27, 2018, http://​chandra​.harvard​.edu/​photo/​2006/​1e0657/ .