- Shapley Supercluster
The Shapley Supercluster (Shapley Concentration) is the largest concentration of
galaxies in 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 millionlight years from the Milky Way.In recent times, the Shapley
supercluster was rediscovered bySomak 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 fromUK Schmidt Telescope Sky survey plates, using theAutomated Plate Measuring Facility (APM) at theUniversity of Cambridge in England. In this paper, the Supercluster was named afterHarlow Shapley , in recognition of his pioneering survey of galaxies in which this concentration of galaxies was first seen. Around the same time,Roberto Scaramella and co-workers had also noticed a remarkable concentration of clusters in theAbell catalogue ofclusters 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)] ]History
In the late 1920s,
Harlow Shapley and his colleagues at theHarvard College Observatory started a survey of galaxies in the southern sky, using photographic plates obtained at the 24-inchBruce telescope atBloemfontein, South Africa . By 1932, Shapley reported the discovery of 76,000 galaxies brighter than 18thapparent magnitude in 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 Supercluster and theVirgo supercluster ), but found a `cloud' in the constellation ofCentaurus 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 theVirgo cluster , from the average diameters of the galaxies.Current interest
The Shapley Supercluster lies very close to the direction in which the
Local Group of galaxies (including our Galaxy) is moving with respect to theCMB frame . This has led many to speculate that the Shapley Supercluster may indeed be one of the major causes of our peculiar motion (theGreat Attractor ), and has led to a surge of interest in this Supercluster.References
External links
* [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]ee also
*
Great Attractor
*Hydra-Centaurus Supercluster
*Norma Cluster
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