X Rays from the Perseus Cluster Core . ... NASA Explanation: The Perseus Cluster of thousands of galaxies, 250 million light-years distant, is one of the most massive objects in the Universe and the brightest galaxy cluster in the x-ray sky . At its core lies the giant cannibal galaxy Perseus A (NGC 1275) , accreting matter as gas and galaxies fall into it. This deep Chandra Observatory x-ray image spans about 300,000 light-years across the galaxy cluster core. ... NASA Official: Jay Norris. ...