Tully Discovers the Pisces-Cetus Supercluster Complex Summary

  • Last updated on November 10, 2022

R. Brent Tully posed a challenge to existing theories of galaxy formation when he mapped a complex of galaxy superclusters more than one billion light-years in diameter, possibly the largest structure in the observable universe.

Summary of Event

R. Brent Tully announced in December, 1987, that he had found a plane of galaxies occupying about one-tenth of the visible universe, a structure larger than any previously suspected. This Pisces-Cetus supercluster complex posed a major problem for the principal theory about the origin and development of the cosmos: It seemed to conflict with a major piece of evidence supporting the theory, which suggested that the distribution of galaxies in the universe should be fairly uniform. Tully’s analyses showed otherwise; the universe, Tully noted, is “lumpy.” Pisces-Cetus supercluster complex[Pisces Cetus supercluster complex] Astronomy;galaxies Galaxies [kw]Tully Discovers the Pisces-Cetus Supercluster Complex (1986-1987) [kw]Discovers the Pisces-Cetus Supercluster Complex, Tully (1986-1987) [kw]Pisces-Cetus Supercluster Complex, Tully Discovers the (1986-1987) [kw]Supercluster Complex, Tully Discovers the Pisces-Cetus (1986-1987) Pisces-Cetus supercluster complex[Pisces Cetus supercluster complex] Astronomy;galaxies Galaxies [g]North America;1986-1987: Tully Discovers the Pisces-Cetus Supercluster Complex[05940] [g]United States;1986-1987: Tully Discovers the Pisces-Cetus Supercluster Complex[05940] [c]Science and technology;1986-1987: Tully Discovers the Pisces-Cetus Supercluster Complex[05940] [c]Astronomy;1986-1987: Tully Discovers the Pisces-Cetus Supercluster Complex[05940] Tully, R. Brent Fisher, J. Richard Vaucouleurs, Gérard Henri de Abell, George Ogden

Over the course of the twentieth century, astronomers observed ever-larger groupings of stars that theorists struggled to explain. In the 1920’s, Edwin Powell Hubble Hubble, Edwin Powell proved that certain “spiral nebulas” lie outside Earth’s galaxy, the Milky Way; these can be larger than our galaxy and are moving away from Earth at very high velocities. Spiral nebulas Hubble’s observations and calculations revealed that the universe not only is much larger than was thought at the time but also is expanding—to the surprise of cosmologists, who assumed the universe to be static. To account for this expansion, many astronomers accepted various versions of the big bang theory, Big bang theory Universe;expansion which Georges Lemaître Lemaître, Georges formulated in 1927. Lemaître proposed that an explosion of the “primordial atom” sent matter hurling in all directions, matter that coalesced into the galaxies of the modern universe.

Logically, such an explosion would fill the universe evenly in all directions, but evidence began to mount even in the 1930’s that a perfectly even distribution of matter is not the case. Fritz Zwicky’s Zwicky, Fritz observations first demonstrated that galaxies tend to group together, and subsequent optical and radio astronomy surveys of the sky discerned ever-larger collections of galaxies bound together by gravity. The idea that galaxies gather in clusters of about 30 million light-years in diameter came to be widely accepted. (A light-year is the distance light travels in one year—about 9.46 trillion kilometers, or 5.88 trillion miles.) These clusters, in turn, often form structures 100 million light-years in diameter, called superclusters, or line up in long chains. The Milky Way, Milky Way galaxy for example, is part of a modest group of galaxies near the Virgo cluster, which is the center for the local supercluster. Furthermore, in 1981, scientists announced the discovery of voids as large as superclusters between groups of galaxies.

Tully was among the astronomers who investigated large-scale structures in the universe during the 1970’s and 1980’s and was a leading advocate for the existence of the local supercluster, along with Gérard Henri de Vaucouleurs and Antoinette de Vaucouleurs, despite general resistance to the idea. Identification of such structures depended on the mapping of the vast region beyond the Milky Way. Tully’s interest in this project began in 1972 as he and J. Richard Fisher were completing their doctoral work at the University of Maryland. Tully and Fisher collaborated on a project to survey all nearby galaxies, and in the course of their work they developed a method to measure distances to spiral galaxies (one of several distinct galaxy classes) based on the correlation between a galaxy’s brightness and the width of the neutral hydrogen line in the spectrum of its light. This “Tully-Fisher relation” Tully-Fisher relation[Tully Fisher relation] became a widely accepted intergalactic yardstick.

Tully prepared the first prototypes of ten maps while he was working at the Observatoire de Marseille in France, and revised prototypes were made at the National Radio Astronomy Observatory’s drafting department in Charlottesville, Virginia. Meanwhile, Tully and Fisher continued to map the skies, using earlier surveys of galaxy groups by George Ogden Abell and Vaucouleurs and drawing data from radio observatories in both the Northern and the Southern Hemispheres. Tully moved to the Institute for Astronomy at the University of Hawaii in 1982 and enlisted the help of cartographer Jane Eckelman Eckelman, Jane of Manoa Mapworks in Honolulu in compiling accurate visual representations of the data that were accumulating. This was difficult, Tully and Fisher later wrote, because they still were not sure what they were trying to map; additionally, they wanted to produce complicated three-dimensional graphics to correspond to sectors of the sky.

Tully and Fisher’s work culminated in 1987 with the publication of the Nearby Galaxies Catalog Nearby Galaxies Catalog (Tully and Fisher) and Nearby Galaxies Atlas. Nearby Galaxies Atlas (Tully and Fisher) While preparing the maps for publication, Tully searched for the edge of the local supercluster. It became increasingly apparent that the supercluster was far larger than had been suspected. He examined densely populated (or “rich”) clusters in the Northern Hemisphere, their motion relative to one another, and their distances from one another, and then used a supercomputer to plot their distribution from various perspectives. He found that the clusters appeared to lie in a plane and that this extension of the local supercluster corresponded to a plane of rich clusters in the southern galactic hemisphere centered about 650 million light-years from the Milky Way in the Pisces-Cetus region of the sky.

R. Brent Tully.

(Institute of Astronomy, Honolulu)

The chance that this correlation of flattened distribution was an accident of random motion, his analyses suggested, was statistically small. Tully concluded that the planes of clusters must be elements of the same structure. In the Nearby Galaxies Atlas, Tully and Fisher call this structure the Pisces-Cetus supercluster complex; it comprises the Pisces-Cetus supercluster, the Perseus-Pegasus chain, the Virgo-Hydra-Centarus supercluster, the Pegasus-Pisces chain, and the Sculptor region. The entire complex is about 1 billion light-years in length and 150 million light-years in width, making it the largest single structure in the observable universe. Additionally, Tully and Fisher list four other supercluster complexes, in the Hercules-Corona Borealis, Aquarius, Ursa Major, and Leo sectors.

Tully published his findings in two articles in the Astrophysical Journal, on April 1, 1986, and December 1, 1987. By the time the second article appeared, science writers in newspapers and magazines already had heralded the discovery, emphasizing that it did not seem to fit established concepts of the universe. Tully concluded the December article by pointing out that his discovery posed an obvious challenge to most popular theories of galaxy formation.

Nevertheless, the supercluster complex was not an established fact. Tully acknowledged that the evidence from his surveys was suggestive but not conclusive. The center of the Pisces-Cetus supercluster complex, for example, lies in the southern galactic hemisphere, and knowledge of clusters in that area is still relatively sketchy; furthermore, the center of the Milky Way blocks direct observation of a section of the structure. Therefore, Tully’s map of the Pisces-Cetus plane is, as he himself put it, full of holes. He had detected an alignment of planes rather than an outright connection. Still, he insisted that the alignment appears too exact to be dismissed as chance.


Astronomers and astrophysicists reacted with interested skepticism to Tully’s conclusions. Well-known deficiencies existed in some of the data on which he depended (for example, Abell’s catalog of clusters), and some insisted that there simply was not enough knowledge about very-large-scale structures in the universe to distinguish actual structures from the illusory effects of imperfect observation. None was willing to dismiss Tully’s work, however, and further surveys of galaxies also suggested structures larger than superclusters.

By the mid-1980’s, the big bang theory had undergone major modifications, but a central feature of the theory still predicted that matter in the modern universe should be homogeneous in distribution because matter in the early universe expanded at a rapid, uniform rate. Radio astronomers uncovered dramatic supporting evidence for the theory in the 1960’s, when they detected background radiation left over from the big bang; the radiation reaches Earth with almost exactly the same intensity from all directions, as would be expected if it were produced by a single explosion. Cosmologists were able to accommodate structures the size of clusters of galaxies in the big bang theory, but when voids and superclusters were found, they had increasing difficulty explaining how the cosmic background radiation could be uniform while matter was clumping in large, intricate structures.

Tully’s supercluster complexes presented a new order of difficulty and further observational evidence that the universe is not homogeneous. These discoveries inspired theorists to hypothesize novel, sometimes bizarre, physical phenomena—based on both astrophysical and particle physics theories—that could cause galaxies and their groupings to form. The most widely accepted theory was that soon after the big bang, the universe underwent a sudden, temporary inflation, often called the “cosmic burp.” Cosmic burp theory This sent gravity rippling through space, which created density fluctuations in the universe’s matter and fostered the formation of structures. Another theoretical addition suggested that the light-producing and light-reflecting matter that is observed accounts for only about 10 percent of the total matter of the universe. The “missing matter” is cold and dark—invisible to contemporary instruments—and spread evenly through the cosmos: Visible matter is like froth on top of dark beer, one astrophysicist remarked. Yet a third theory proposed the existence of extremely thin, high-density, high-energy tubes of space-time that drift through the universe. These “cosmic strings” Cosmic string theory can be either infinitely long or closed in loops, and their strong gravity could draw matter into galaxies and clusters.

Like most astronomers, Tully found aspects of all these theories useful in explaining the results of his observations and measurements. The proliferation of theories to reconcile observed phenomena to physical laws, as they are understood, often precedes a breakthrough in science. The discovery of increasingly large structures in the universe—Tully’s supercluster complexes among them—led some observers to speculate that science may be on the verge of a new basic understanding of the environment as revolutionary as Albert Einstein’s theory of general relativity (1916) or Edwin Powell Hubble’s proof that the universe is expanding (1929). Pisces-Cetus supercluster complex[Pisces Cetus supercluster complex] Astronomy;galaxies Galaxies

Further Reading
  • citation-type="booksimple"

    xlink:type="simple">Bartusiak, Marcia. Thursday’s Universe: A Report from the Frontier on the Origin, Nature, and Destiny of the Universe. New York: Times Books, 1986. Entertaining, lucidly written account of astronomical knowledge and theory up to the mid-1980’s. Although this volume appeared before Tully’s findings on supercluster complexes were published, it introduces readers to related phenomena, such as voids and bubbles, thoroughly and comprehensibly. An excellent book for newcomers to astrophysics.
  • citation-type="booksimple"

    xlink:type="simple">Cornell, James, ed. Bubbles, Voids, and Bumps in Time: The New Cosmology. New York: Cambridge University Press, 1989. Collection of six articles discusses developments in cosmology and astrophysics. Margaret J. Geller’s essay on mapping the universe discusses a study of galaxies much like Tully’s. The essays are all readable, often amusing, and accessible to readers who are willing to stretch their imaginations.
  • citation-type="booksimple"

    xlink:type="simple">Ferguson, Kitty. Measuring the Universe: Our Historic Quest to Chart the Horizons of Space and Time. New York: Walker, 1999. Examines the history of humankind’s efforts to measure and understand the size and structure of the universe. Chapter 7 includes discussion of Tully’s work. Features glossary and index.
  • citation-type="booksimple"

    xlink:type="simple">Greenstein, George. The Symbiotic Universe: Life and Mind in the Cosmos. New York: William Morrow, 1988. A speculative, provocative contemplation as well as a book about science. Attempts to relate contemporary discoveries about the universe to large questions such as “Where did life come from?” and “Is there a plan behind it all?” Explains astrophysical matters, such as theories about galactic clustering, in a loose but clear style.
  • citation-type="booksimple"

    xlink:type="simple">Gregory, Stephen A. “The Structure of the Visible Universe.” Astronomy 16 (April, 1988): 42-47. Excellent, concise article by an astronomer whose specialty is the universe’s large-scale structure. Discusses in a clear manner the methods of mapping voids, superclusters, and complexes of superclusters as well as the difficulties in obtaining sufficient data.
  • citation-type="booksimple"

    xlink:type="simple">Hodge, Paul W. Galaxies. Cambridge, Mass.: Harvard University Press, 1986. Explains galactic evolution, structures, types, clustering, and spacing, although not supercluster complexes. Discusses the Milky Way and nearby galaxies in a pleasing, informative style. Includes a wealth of photographs and illustrations.
  • citation-type="booksimple"

    xlink:type="simple">Tully, R. Brent. “More About Clustering on a Scale of 0.1 c.” Astrophysical Journal 323 (December 1, 1987): 1-18. The primary scientific vehicle for Tully’s conclusions concerning supercluster complexes. Only a reader trained in astrophysics will follow the arguments fully, but a college-level knowledge of astronomy is sufficient to understand portions of it.
  • citation-type="booksimple"

    xlink:type="simple">Tully, R. Brent, and J. Richard Fisher. Nearby Galaxies Atlas. Cambridge, England: Cambridge University Press, 1987. Beautiful collection of color-coded, foldout, two- and three-dimensional maps of galaxies and clusters in a very large format. Indispensable for helping one to visualize the structures of superclusters and supercluster complexes.
  • citation-type="booksimple"

    xlink:type="simple">Zeilik, Michael, and Stephen A. Gregory. Introductory Astronomy and Astrophysics. 4th ed. Monterey, Calif.: Brooks/Cole, 1997. Information-packed textbook is aimed at serious undergraduate-level astronomy and astrophysics students. Presents excellent discussions of concepts and includes outstanding tables, diagrams, and illustrations.

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