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.