Great Attractor

The Great Attractor is a region of enhanced gravitational attraction in the local universe. It lies in the general direction of the Norma Cluster and the Hydra–Centaurus Supercluster, approximately 150–250 million light-years from the Milky Way. Its presence was inferred from the peculiar motions of galaxies, which deviate from the motion expected solely from the expansion of the universe. The term does not refer to a single galaxy, galaxy cluster, or compact astronomical object. Instead, it describes a broad concentration of matter and an associated minimum in the local gravitational-potential and velocity fields. Early models attributed a mass of approximately 1016 solar masses (M☉) to the region. Later observations indicated that the motion of nearby galaxies cannot be explained by the Great Attractor region alone and that more distant structures, particularly the Shapley Supercluster, also contribute substantially. The region is difficult to observe at visible wavelengths because it lies behind the galactic plane of the Milky Way, within the Zone of Avoidance. Dust, gas, and foreground stars obscure many background galaxies in this part of the sky. Astronomers therefore study the area using X-ray, radio, infrared, and neutral-hydrogen observations, which penetrate the obscuring material more effectively than visible light. The Great Attractor was incorporated into the definition of the Laniakea Supercluster in 2014. Under that definition, Laniakea is a basin of attraction whose galaxy flows converge approximately toward the Norma and Centaurus regions. More recent reconstructions using the larger Cosmicflows-4 catalogue have suggested that Laniakea may not be an independent basin and may instead form part of a substantially larger basin associated with the Shapley concentration.