Shapley Supercluster

Lore & Background

In 1930, Harlow Shapley and his colleagues at the Harvard College Observatory started a survey of galaxies in the southern sky, using photographic plates obtained at the 24-inch Bruce telescope at Bloemfontein, South Africa. By 1932, Shapley reported the discovery of 76,000 galaxies brighter than 18th apparent magnitude in a third of the southern sky, based on galaxy counts from his plates. In this catalog, Shapley could see most of the 'Coma-Virgo cloud' (now known to be a superposition of the Coma Supercluster and the Virgo Supercluster), but found a 'cloud' in the constellation of Centaurus to be the most striking concentration of galaxies. He found it particularly interesting because of its 'great linear dimension, the numerous population and distinctly elongated form'. This can be identified with what we now know as the core of the Shapley Supercluster. Shapley estimated the distance to this cloud to be 14 times that to the Virgo Cluster, from the average diameters of the galaxies. In recent times, the Shapley Supercluster was named by Somak Raychaudhury, from a survey of galaxies from UK Schmidt Telescope Sky survey plates, using the Automated Plate Measuring Facility (APM) at the University of Cambridge in England. Around the same time, Roberto Scaramella and co-workers had also noticed the Shapley Supercluster in the Abell catalogue of clusters of galaxies: they had named it the Alpha concentration.

The Shapley Supercluster (SCC) is described as a miniature universe that extends over ≈260 megaparsecs (Mpc) and covers a redshift range from 0.033 to 0.06 (with a mean redshift z = 0.048). Its core region, with the right ascension ranging between 198 and 204 degrees and declination ranging between −34 and −29 degrees, includes 11 clusters and groups with masses in the range M500 ≈ (1–6)×10^14 M☉. Among these, A3558 and A3528 are merging X-ray clusters that form two complex structures in the centre and in the outskirts of SSC. The high-density core of the Shapley supercluster is probably the largest among the collapsing cores of superclusters in the local Universe with a mass around 1.3×10^16 M☉ and a radius of 12.4 Mpc. In another research paper, it states that Shapley Supercluster consist of 28 galaxy clusters. In another research paper, Shapley Supercluster is detected to have three concentration areas: the central concentration (Abell 3556, Abell 3558, Abell 3560, Abell 3564, Abell 3566), a second concentration (Abell 3528, Abell 3530, Abell 3532), and a third concentration known as 'Front Eastern Wall' (Abell 3571, Abell 3572, Abell 357).

Reader's Guide

The Shapley Supercluster lies very close to the direction in which the Local Group of galaxies (including our galaxy) is moving with respect to the cosmic microwave background (CMB) frame of reference. This has led many to speculate that the Shapley Supercluster may be one of the major causes of our galaxy's peculiar motion—the Great Attractor may be another—and has led to a surge of interest in this supercluster. It has been found that the Great Attractor and all the galaxies in our region of the universe (including our galaxy, the Milky Way) are moving toward the Shapley Supercluster. In 2017 it was proposed that the movement towards attractors like the Shapley Attractor in the supercluster creates a relative movement away from underdense areas, that may be visualized as a virtual repeller. This approach enables new ways of understanding and modelling variations in galactic movements. The nearest large underdense area has been labelled the dipole repeller. The supercluster's role as a major gravitational attractor influencing the motion of our Local Group and the Great Attractor underscores its significance in understanding large-scale flows and the structure of the local universe.

Did You Know?

• The Shapley Supercluster was first seen as a 'cloud' in Centaurus by Harlow Shapley in the 1930s.
• It is one of the largest bound concentrations of galaxies, pulling itself together rather than expanding with the universe.
• The Shapley Supercluster may contain the Laniakea Supercluster, which includes the Milky Way.