A purported concentration of matter in the direction of the constellations Hydra and Centaurus which may be pulling surrounding galaxies, including ours, towards it. The Great Attractor is calculated to have a mass about 5 × 1016 solar masses and to lie about 150 million l.y. from our Galaxy. Its existence was originally inferred from studies of the motions of galaxies with respect to the Hubble flow. Although there clearly is a concentration of galaxies at the place where the Great Attractor supposedly lies, more recent studies indicate that the observed bulk flows of galaxies are probably due to the concerted pull of several distinct clusters, so that the Great Attractor is not a single object.