Gérard Henri de Vaucouleurs observed and delineated the local supercluster of galaxies, sparking the study of the large-scale structure of the universe.

Astronomers were able to observe dim patches of light, or nebulas Nebulas
Astronomy;nebulas , in the sky long before they discovered the nature of these nebulas, which today are known to be galaxies. Several early observers made lists or catalogs of these objects; for example, in 1888, Johann Louis Emil Dreyer’s Dreyer, Johann Louis Emil
New General Catalogue of Nebulae and Clusters of Stars. New General Catalogue of Nebulae and Clusters of Stars (Dreyer)
Astronomy;galaxies
Galaxies
Superclusters, galactic
Local supercluster of galaxies
[kw]De Vaucouleurs Identifies the Local Supercluster of Galaxies (Early 1950’s)[Devaucouleurs Identifies the Local Supercluster of Galaxies]
[kw]Local Supercluster of Galaxies, De Vaucouleurs Identifies the (Early 1950’s)
[kw]Supercluster of Galaxies, De Vaucouleurs Identifies the Local (Early 1950’s)
[kw]Galaxies, De Vaucouleurs Identifies the Local Supercluster of (Early 1950’s)[Galaxies, Devaucouleurs Identifies the Local Supercluster of]
Astronomy;galaxies
Galaxies
Superclusters, galactic
Local supercluster of galaxies
[g]Australia;Early 1950’s: De Vaucouleurs Identifies the Local Supercluster of Galaxies[03050]
[c]Astronomy;Early 1950’s: De Vaucouleurs Identifies the Local Supercluster of Galaxies[03050]
[c]Science and technology;Early 1950’s: De Vaucouleurs Identifies the Local Supercluster of Galaxies[03050]
Vaucouleurs, Gérard Henri de
Abell, George Ogden
Shane, Charles Donald
Wirtanen, Carl Alvan
Neyman, Jerzy
Scott, Elizabeth Leonard

In the early 1920’s, a debate over the nature of the so-called spiral nebulas came to a head and was resolved. (These nebulas received their name from their spiral shape.) One school of thought was that these spiral nebulas were pieces of the earth’s star system, the Milky Way—relatively nearby, small objects. Another theory held that they were distant, very large, independent star systems. In 1924, Edwin Powell Hubble Hubble, Edwin Powell was able to settle the debate by determining the distance to one of the spiral nebulas, the Andromeda nebula. The distance he found was a large one, which indicated that the nebula was, in fact, a huge system, independent of the Milky Way. Harlow Shapley Shapley, Harlow , in the 1920’s, discovered the dimensions and rough structure of the Milky Way galaxy Milky Way galaxy , and the work of Hubble and Shapley brought about the beginnings of the present picture of the universe: The Milky Way is a spiral galaxy in a universe that contains other galaxies of various shapes and sizes.

Astronomers began to study how galaxies are distributed in the sky. They did this by examining plates of the sky taken with large telescopes over long exposure times, which revealed many galaxies. They then counted the galaxies and noted their positions. Some of this work was done with photographs taken using traditional methods. The sky surveying process was changed in 1930 when the Schmidt camera Schmidt camera was developed by Bernhard Schmidt Schmidt, Bernhard . Large areas of sky could be photographed relatively quickly using this new camera, and it became easier for astronomers to make detailed surveys of the entire sky. Whether done with the Schmidt camera or with traditional methods, surveys of the night sky were a useful piece of work done by the new large telescopes in the first half of the twentieth century.

The sky surveys revealed interesting information about the way that galaxies appear to be distributed in space. Even before the nature of the spiral nebulas was known, astronomers had noted that spiral nebulas appear in clusters. The positions given in Dreyer’s catalog reveal this information, and in 1922, a band of nebulas stretching nearly 40 degrees across the northern sky was observed by the English astronomer J. H. Reynolds Reynolds, J. H. . Knut Lundmark also noted this feature. (These may be considered the first observations of the local supercluster, although the observers did not identify or study what they observed.)

In addition to identifying the local group (a group of nearby galaxies, of which the Milky Way is a part), astronomers identified other groupings of galaxies. The Coma cluster and the Virgo cluster of galaxies were defined and named for the constellations in which they appear. Hubble photographed faint galaxies, so faint that he thought he was seeing as far into the universe as he could and that he was witnessing a limit to the phenomenon of clustering. An earlier scheme proposed by C. V. L. Charlier Charlier, C. V. L. suggested that there was a hierarchy of structure to the universe, with clusters of galaxies making up clusters of clusters, which in turn made up still larger structures. Hubble’s observations seemed to indicate that this hierarchy was not likely to exist.

Relative positions of the galaxy clusters that form the “local supercluster.”

By 1950, astronomers had gathered enough information about clusters of galaxies that they could arrive at a consensus on the general features of the clusters, such as the types of galaxies they contained and the sizes of the clusters. The largest cluster known was the Coma cluster, which contained more than one thousand individual galaxies. The galaxies in clusters were mostly elliptical galaxies (rounded or oval in shape, with no distinguishing structural features), and spirals without much spiral arm structure. Astronomers had also identified so-called field objects: isolated galaxies, mostly spirals, that did not appear to belong to any cluster. It had been suggested that perhaps the group of galaxies in the Virgo area of the sky might contain more than one cluster, but Hubble’s work with faint galaxies seemed to rule out any hierarchical scheme of clustering of clusters.

It was on the basis of a sky survey, completed at Lick Observatory Lick Observatory between 1947 and 1954 by Charles Donald Shane and Carl Alvan Wirtanen, that Elizabeth Leonard Scott and Jerzy Neyman applied the techniques of statistics to the question of the large-scale structure of the universe. Between 1952 and 1954, they published several papers regarding the probabilistic laws that describe clustering, posited that all galaxies belong to clusters, and mentioned the existence of “clouds” of galaxies, which was their term for superclusters.

George Ogden Abell, at the University of California, Los Angeles, used plates taken with a Schmidt camera on Mount Palomar to make a catalog of 2,712 clusters of galaxies, and his work indicated that many of the clusters seemed to be members of superclusters. Fritz Zwicky Zwicky, Fritz , using the plates from the same sky survey, arrived at a different conclusion, similar to Hubble’s: that the clusters do not form still larger clusters. Zwicky’s clusters were, in general, larger than Abell’s, and a single cluster could contain several centers of concentration, so perhaps he defined as a cluster what Abell would have called a supercluster.

In the early 1950’s, Gérard Henri de Vaucouleurs first defined and described what is called the local supercluster. De Vaucouleurs went to work at the Mount Stromlo Observatory in Australia to update the Shapley-Ames catalog Shapley-Ames catalog[Shapley Ames catalog] of bright galaxies, a standard tool for astronomers. While doing this work, he observed that the local group was located at the edge of a much larger grouping of clusters of galaxies. He referred to this larger grouping as a supergalaxy, and further estimated that other supergalaxies or “clouds,” as he also referred to them, might exist as well.

De Vaucouleurs estimated the local supercluster to be approximately 50 million light-years across and to be roughly disk shaped. The supercluster is centered on the Virgo cluster of galaxies Virgo cluster of galaxies , about 50 million light-years distant, and the local group of galaxies is a relatively remote outrider of the supercluster. De Vaucouleurs also identified what appeared to be another supercluster, which he called the southern supergalaxy; he posited that the local supercluster is neither unique nor unusual. De Vaucouleurs has gone on to conduct many studies of the superclustering phenomenon and of cosmology. Astronomers estimate the local supercluster to be about 100 million light-years across and to have a total mass about 1 quadrillion times that of the sun. Astronomers also have discovered fine detail in the local supercluster and other superclusters. At first, de Vaucouleurs’s work on the local supercluster was largely ignored by the astronomy community; his persistence in this work eventually gained recognition. The study of the large-scale structure of the universe is an exciting field in astronomy.

More sky surveys and analysis of existing surveys have been done since the early work in the 1950’s. Shane and Wirtanen at Lick Observatory made painstaking counts of galaxies in their survey, which measured out to a distance of about 1 billion light-years. These data were used by Phillip James Edwin Peebles Peebles, Phillip James Edwin to make a map of more than 1 million galaxies. This map reveals structure in the distribution of galaxies.

This map, however, is only a two-dimensional distribution; it does not differentiate between near galaxies and far ones, and it takes into account only a galaxy’s coordinates on the sky. Astronomers also make three-dimensional surveys that take into account the distances of galaxies by using the redshifts of galaxies. Hubble and Milton Lasell Humason Humason, Milton Lasell found, in the late 1920’s, that light from galaxies is Doppler-shifted toward the red because of the motion of galaxies outward from the big bang, which appears to carry each galaxy away from all the others. The magnitude of redshift is related to the speed of recession, which, in turn, is related to the distance of the galaxy. Astronomers use redshifts Redshifting to determine the distances of galaxies, and then map out a three-dimensional plot of the galaxies’ distribution in space. New technology such as CCDs (charge-coupled devices) enabled astronomers to complete seven three-dimensional surveys of the sky, which have revealed some fascinating results.

Several groups of people have worked on superclusters of galaxies: a team from the Center for Astrophysics, led by Marc Davis and John Huchra, worked at Mount Hopkins; Stephen Gregory, Laird Thompson, and William Tifft worked at Kitt Peak; Brent Tully and Richard Fisher mapped the local supercluster. In addition to the local supercluster, others have been identified: the Hercules, Coma, and Perseus-Pisces superclusters. Common features of these superclusters have been identified. The hypothesis of de Vaucouleurs—that superclusters exist as organized structures—has been confirmed. Fine structure has been discovered, such as filaments and streamers, or strings of galaxies that link the various parts of the superclusters.

In addition, astronomers have discovered voids, or spaces, in which no bright galaxies appear. Gregory’s group was the first to identify a void, in the Coma supercluster, and at first they thought it was a fluke. Nevertheless, others soon identified more small voids. The first really large gap in space was found by people who were not mapping superclustering structures, but instead were trying to find an average density of galaxies in the universe. Robert Kirshner, Augustus Oemler, and Paul Schechter chose a portion of sky near the constellation Boötes and set out to count galaxies per unit volume of space. They found a huge cavity in space that contained no bright galaxies at all. The study of these voids is a major puzzle for cosmologists.

The structure of superclusters may have much to teach astronomers about how the universe cooled and formed after the big bang. This field is at the forefront of cosmological research, and may reveal even more startling information about the large-scale structure of the universe and how it came to be. Astronomy;galaxies
Galaxies
Superclusters, galactic
Local supercluster of galaxies

• Bartusiak, Marcia. Thursday’s Universe. New York: Times Books, 1986. Chapter 7, “Celestial Tapestry,” gives an excellent overview of the current picture of the large-scale structure of the universe. Discusses superclustering, voids, and the observational methods used to study them; gives information on the properties of some superclusters. Written for the layperson, it takes the reader into the world of astronomers and the work they are doing. Includes a bibliography, some photographs.
• Gregory, Stephen A. “The Structure of the Visible Universe.” Astronomy 16 (April, 1988): 42-47. Written by an astronomer who has conducted important research in large-scale structure of the universe. Gives a good overview of the history of research into the distribution of galaxies, the current methods being used, and current results. Includes photographs and a map of the Perseus supercluster.
• Gregory, Stephen A., and Laird A. Thompson. “Superclusters and Voids in the Distribution of Galaxies.” Scientific American 246 (March, 1982): 106-114. Cowritten by two astronomers who have done research on superclusters. Gives the history of the discovery of clustering and superclustering of galaxies, and an overview of current work in the field, including cosmological implications. Includes maps illustrating the superclusters, and drawings.
• Melott, Adrian L. “Recreating the Universe.” Astronomy 16 (May, 1988): 42-47. Discusses the cosmological and theoretical implications of current knowledge of the large-scale structure of the universe. Gives information on how astronomers use computer models to simulate processes suggested by various theories of how the universe formed and changed over time, and compares the results with the universe as it is observed. Illustrated with computer graphics.
• Vaucouleurs, Gérard Henri de. Discovery of the Universe: An Outline of the History of Astronomy from the Origins to 1956. London: Faber & Faber, 1956. Written immediately after de Vaucouleurs’s research that indicated the existence of the local supercluster; contains his views of his work. Although astronomers’ knowledge has expanded greatly and in some cases changed since this was written, it is valuable for de Vaucouleurs’s own writings on his discovery. Contains a drawing of the postulated structure of the local supercluster.
• Zeilik, Michael. Astronomy: The Evolving Universe. 9th ed. New York: Cambridge University Press, 2002. An introductory textbook that contains a brief, but excellent, discussion of superclusters, complete with drawings and maps, including a photograph of the map done by Peebles. Discusses redshift measurements, intergalactic matter, and related topics of interest. Intended for nonscience majors. Includes photographs and drawings, study exercises, further readings, and a glossary.

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