A nearby massive galaxy cluster behind the Milky Way

THE recession velocities of relatively nearby galaxies show systematic deviations from a uniform expansion field. These deviations indicate the presence of the 'Great Attractor' - a large concentration of mass (∼ 5 × 1016 solar masses) that lies in the direction of the southern Milky Way1,2. Attempts to quantify both the nature and extent of the Great Attractor3-11 have been hampered by the fact that it is largely hidden by the disk of the Milky Way. Although there is an excess of galaxies in this region12, no dominant galaxy cluster or other concentration of mass has hitherto been identified. Here we present results from a survey of galaxies obscured (or partially obscured) by the southern Milky Way. Our results show that a previously identified galaxy cluster, Abell 3627, which lies only 9°from the predicted centre of the Great Attractor13, is very massive (∼ 5 × 1015 solar masses). The cluster's redshift is also near that predicted for the core of the Great Attractor2,3,12-14, suggesting that it lies at or near the bottom of the Attractor's gravitational potential well.