Virgo Supercluster

Lore & Background

Beginning with the first large sample of nebulae published by William and John Herschel in 1863, an excess of nebular fields in the constellation Virgo was noted. In the 1950s, French–American astronomer Gérard de Vaucouleurs argued this excess represented a large-scale galaxy-like structure, coining the term 'Local Supergalaxy' in 1953, changed to 'Local Supercluster' in 1958. Harlow Shapley suggested the term 'Metagalaxy' in 1959. Debate persisted through the 1960s and 1970s as to whether the Local Supercluster was a real structure or a chance alignment, resolved by large redshift surveys of the late 1970s and early 1980s that showed a flattened concentration of galaxies along the supergalactic plane.

In 1982, R. Brent Tully described the basic structure: an appreciably flattened disk containing two-thirds of the supercluster's luminous galaxies, and a roughly spherical halo containing the remaining third. The disk is a thin (~1 Mpc) ellipsoid with a long axis/short axis ratio of at least 6 to 1, possibly as high as 9 to 1. Data from the Two-degree-Field Galaxy Redshift Survey (2dF) released in June 2003 showed the Virgo Supercluster represents a typical poor supercluster of rather small size, with one rich galaxy cluster at its center surrounded by filaments of galaxies and poor groups. The main body, the Virgo Strand, connects the Hydra-Centaurus and Perseus–Pisces Superclusters.

A 2014 study indicated the Virgo Supercluster is only part of an even greater supercluster centered on the Great Attractor, the Laniakea Supercluster, which subsumes the former as a component. This redefinition uses basins of attraction rather than high-density regions; such basins have been proposed to be called 'supercluster cocoons' to distinguish them from traditional superclusters like Virgo.

Reader's Guide

The Virgo Supercluster's significance lies in its role as the local supercluster containing the Milky Way and the Local Group, making it the primary large-scale structure for studying our cosmic neighborhood. Its identification resolved a decades-long debate about whether the observed concentration of galaxies in Virgo was a real structure or a chance alignment, confirmed by redshift surveys. The supercluster's structure—a thin disk and a spherical halo—provided an early model for supercluster morphology. Its mass-to-light ratio of about 300 times the solar ratio is a key argument for the existence of large amounts of dark matter. The 2014 redefinition of the local supercluster as Laniakea, a basin of attraction centered on the Great Attractor, reframed the Virgo Supercluster as a component of a larger structure, highlighting the evolving understanding of cosmic hierarchy. The Virgo Supercluster also serves as a typical example of a poor supercluster, lacking a high-density core, and its distribution of galaxies in clouds and voids (like soap bubbles) illustrates the filamentary nature of the cosmic web.

Did You Know?

• The Virgo Supercluster contains at least 100 galaxy groups and clusters within its diameter of 45 megaparsecs.
• The Local Group, containing the Milky Way and Andromeda, is located near one edge of the Virgo Supercluster.
• The Virgo Supercluster's volume is roughly 7,000 times that of the Local Group.
• A 2014 study indicated the Virgo Supercluster is only a part of the even larger Laniakea Supercluster.