Shapley Supercluster

Shapley Supercluster is the most massive concentration of galaxy clusters in the nearby universe, located approximately 650 million light-years away in the direction of the constellation Centaurus. Its discovery provided crucial evidence for the existence of large-scale structure in the cosmos and plays a central role in explaining the motion of our Local Group through space. The supercluster's immense gravitational influence is a key component in understanding the dynamics of our local cosmic neighborhood and the mystery of the Great Attractor.

Discovery and observation

The existence of this massive concentration was first noted in the 1930s by the pioneering astronomer Harlow Shapley during his extensive studies of galaxy distributions using the facilities at Harvard College Observatory. Subsequent systematic surveys, particularly those conducted with the UK Schmidt Telescope as part of the Southern Sky Survey, began to map its true extent. Detailed studies were propelled by missions like the ROSAT X-ray observatory, which revealed the hot intracluster medium binding its clusters, and later by the Two Micron All Sky Survey (2MASS), which penetrated dust to map stellar mass. Modern observatories, including the European Southern Observatory and the Chandra X-ray Observatory, continue to probe its complex dynamics and composition.

Structure and composition

The core of the supercluster is dominated by a dense chain of massive, X-ray luminous galaxy clusters, with the central Abell 3558 complex acting as its gravitational anchor. This core is surrounded by other major clusters such as Abell 3565, Abell 3571, and Abell 3572, all interconnected by vast filaments of galaxies and dark matter. Spectroscopic surveys from instruments like the Anglo-Australian Telescope have measured the redshifts of thousands of member galaxies, confirming its three-dimensional structure and complex internal motions, including mergers and subcluster infall. The total mass, dominated by dark matter, is estimated to be on the order of ten thousand times that of the Milky Way.

Significance in cosmology

As the richest supercluster within a billion light-years, it serves as a premier laboratory for studying the formation of large-scale structure and the nature of dark matter. Its existence challenged earlier, more uniform models of the universe, such as those stemming from the Cosmic Microwave Background results from COBE, by demonstrating the pronounced clumpiness of matter. Studies of its dynamics provide critical tests for simulations of cosmic structure formation like the Millennium Simulation and inform theories of hierarchical clustering. Its gravitational pull significantly influences the peculiar velocity flow field in our local universe, making it a cornerstone for understanding physical cosmology.

Relation to the Great Attractor

The supercluster is now understood to be a major, but not sole, component of the gravitational anomaly known as the Great Attractor, which influences the motion of the Local Group and the Virgo Supercluster. While initial studies pointed to a concentration in the general direction of Norma, later analyses revealed that the even greater mass of this supercluster lies behind it. The total bulk flow pulling our region of space is now attributed to the combined pull of this supercluster and more distant mass concentrations like the Vela Supercluster and the Horologium-Reticulum Supercluster. This revised understanding resolved key discrepancies in the measured cosmic microwave background dipole from missions like WMAP and Planck.

Category:Superclusters Category:Centaurus