The Shapley Supercluster (Shapley Concentration) is the largest concentration of
galaxiesin our nearby Universe that forms a gravitationally interacting unit, thereby pulling itself together instead of expanding with the Universe. It appears as a striking overdensity in the distribution of galaxies in the constellation of Centaurus, approximately 650 million light yearsfrom the Milky Way.
In recent times, the Shapley
superclusterwas rediscovered by Somak Raychaudhury, [ [http://www.nature.com/nature/journal/v342/n6247/abs/342251a0.html The distribution of galaxies in the direction of the 'Great Attractor' Somak Raychaudhury Nature 342, 251-255 (1989)] ] from a survey of galaxies from UK Schmidt TelescopeSky survey plates, using the Automated Plate Measuring Facility(APM) at the University of Cambridgein England. In this paper, the Supercluster was named after Harlow Shapley, in recognition of his pioneering survey of galaxies in which this concentration of galaxies was first seen. Around the same time, Roberto Scaramellaand co-workers had also noticed a remarkable concentration of clusters in the Abell catalogueof clusters of galaxies: they had named it the "Alpha concentration". [ [http://www.nature.com/nature/journal/v338/n6216/abs/338562a0.html A marked concentration of galaxy clusters: is this the origin of large-scale motions? R. Scaramella et al. Nature 338, 562 (1989)] ]
In the late 1920s,
Harlow Shapleyand his colleagues at the Harvard College Observatorystarted a survey of galaxies in the southern sky, using photographic plates obtained at the 24-inch Bruce telescopeat Bloemfontein, South Africa. By 1932, Shapley reported the discovery of 76,000 galaxies brighter than 18th apparent magnitudein a third of the southern sky, based on galaxy counts from his plates. Some of this data was later published as part of the Harvard galaxy counts, intended to map Galactic obscuration and to find the space density of galaxies.
In this catalog, Shapley could see most of the `Coma-Virgo cloud' (now known to be a superposition of the
Coma Superclusterand the Virgo supercluster), but found a `cloud' in the constellation of Centaurusto 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.
The Shapley Supercluster lies very close to the direction in which the
Local Groupof galaxies (including our Galaxy) is moving with respect to the CMB frame. This has led many to speculate that the Shapley Supercluster may indeed be one of the major causes of our peculiar motion (the Great Attractor), and has led to a surge of interest in this Supercluster.
* [http://eaa.crcpress.com/?action=summary&doc=eaa/2137@eaa-xml&qt= Article on the Shapley Supercluster in the Encyclopedia of Astronomy and Astrophysics]
* [http://www.atlasoftheuniverse.com/superc/shapley.html An atlas of the Universe]
* [http://www.ira.cnr.it/~tventuri/shapley.html The Shapley Concentration]
* [http://www.cfa.harvard.edu/hco/ Harvard College Observatory]
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