A clash of clusters provides another clue to dark matter

This astounding view of galaxy cluster MACSJ0025 demonstrates how ordinary matter and mysterious dark matter interact. The blue cloud-shaped parts flanking the centre show the position of dark matter, mapped by the Advanced Camera for Surveys onboard the NASA/ESA Hubble Space Telescope. The pink middle indicates ordinary matter, charted by NASA’s Chandra X-Ray Observatory. The position of the two matter types shown in the image are explained by MACSJ0025’s origin. It was formed when a pair of large galaxy clusters collided. Ordinary matter in the form of hot gas slowed down and pooled at the centre but ghostly dark matter passed straight through. Hubble used a technique known as gravitational lensing to obtain its data. The light observed was bent by the gravitationally massive galaxy cluster, resulting in an incredibly detailed image. This technique was originally predicted by Einstein. MACSJ0025 is located in the constellation Cetus, the Whale. Credit: NASA, ESA, CXC, M. Bradac (University of California, Santa Barbara, USA), and S. Allen (Stanford University, USA).