The Great Attractor is a hypothesized large mass, about 150 million light-years away in the direction of the Virgo-Hydra-Centaurus superclusters, that seems to be affecting the motions of many nearby galaxies. The amount of mass proposed amounts to tens of thousands of galaxies. However, the nature and even the existence of the Great Attractor are subjects of debate. Some astronomers believe that the Great Attractor may be centered on the rich cluster known as Abell 3627; others propose that, while there may be a cluster of galaxies in the area of the Great Attractor, the large-scale movement of so many superclusters is probably due to the gravitational pull of all clusters combined. One argument against the existence of the Great Attractor is that no one has detected signs of infalling galaxies behind the Attractor. On the other hand, it is possible that this infall may be counteracted by the mass of the more distant Shapley Concentration whose galaxies may be tugging the Great Attractor galaxies the other way.