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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. 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.

Galaxies across a region hundreds of millions of light-years wide display coherent peculiar motions in the direction of the Great Attractor. The Great Attractor region itself participates in a larger-scale flow toward the Shapley concentration.

The Great Attractor was identified during the 1980s by a collaboration informally known as the Seven Samurai: David Burstein, Roger Davies, Alan Dressler, Sandra Faber, Donald Lynden-Bell, Roberto Terlevich, and Gary Wegner. Dressler coined the name "Great Attractor", which became widely used.

These studies identified the Norma Cluster, also known as Abell 3627 or ACO 3627, as one of the principal mass concentrations near the center of the Great Attractor region.

The Great Attractor lies in the direction of the constellations Norma and Triangulum Australe, near Galactic longitude 307° and Galactic latitude 9°.

Correcting for this bias reduced some estimates of the motion directed toward the Great Attractor. On intermediate scales, flows converge in the Hydra–Centaurus and Great Attractor region; on larger scales, the Shapley concentration becomes increasingly important.

The Norma Wall, also called the Great Attractor Wall, is a large galaxy filament extending across the Great Attractor region. Dynamical studies have found that it is a rich and massive cluster whose galaxy velocities and hot intracluster gas make it an important contributor to the gravitational field of the Great Attractor region.

Under this model, galaxy flows within Laniakea converge toward the vicinity of the Norma and Centaurus clusters, near the traditional position of the Great Attractor. Later studies verified that the Laniakea supercluster model is consistent with the structure called the Great Attractor.

The Shapley Supercluster lies substantially farther from the Milky Way than the Norma Cluster and contains one of the greatest known concentrations of galaxies in the nearby universe. It is located in approximately the same broad region of the sky as the Great Attractor but at a greater distance. Studies of the peculiar-velocity field indicate that the Shapley concentration contributes significantly to the motion of the Local Group and the Great Attractor region. The Great Attractor is itself moving generally toward Shapley rather than acting as the ultimate endpoint of all nearby flows. This relationship helps explain why the mass inferred from the original Great Attractor model appeared insufficient to produce the full observed motion of the Milky Way and nearby galaxies.

The Great Attractor is sometimes described in popular accounts as an unidentified object pulling galaxies toward it. "The distribution of galaxies in the direction of the 'Great Attractor'". Vimeo (video). — visualization showing the Great Attractor and surrounding large-scale structures

Quick Facts

• The Norma Wall, also called the Great Attractor Wall, is a large galaxy filament extending across the Great Attractor 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.
• 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.
• "The distribution of galaxies in the direction of the 'Great Attractor'".
• Under this model, galaxy flows within Laniakea converge toward the vicinity of the Norma and Centaurus clusters, near the traditional position of the Great Attractor.

Source material: Wikipedia - "Great Attractor". Adapted and summarized for DiscoverScroll. Original contributors are credited through the linked Wikipedia article. Read original on Wikipedia. CC BY-SA 4.0. Changes were made from the original.