Margaret Joan Geller

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Margaret Joan Geller

Margaret Joan Geller (born 1947) discovered the existence of a Great Wall of galaxies in space that stretches at least 500 Million light-years.

Margaret Joan Geller, an astronomy professor at Harvard University and a senior scientist at the Smithsonian Astrophysical Observatory, helped discover a "Great Wall" of galaxies in space stretching at least 500 million light-years. The existence of this structure, the largest ever seen in the universe, presents a conundrum for theorists dealing with the early universe. She has been mapping the nearby universe for the past sixteen years and has produced the most extensive pictures yet.

Geller was born in Ithaca, New York, on December 8, 1947, to Seymour Geller and Sarah Levine Geller. She received her bachelor's degree at the University of California at Berkeley in 1970, and was a National Science Foundation fellow from 1970 to 1973. Her M.A. followed at Princeton University in 1972, and her Ph.D. thesis, entitled "Bright Galaxies in Rich Clusters: A Statistical Model for Magnitude Distributions," was received at Princeton University in 1975. She was a fellow in theoretical physics at the Harvard-Smithsonian Center for Astrophysics from 1974 to 1976, and a research associate at the center from 1976 to 1980. She was a senior visiting fellow at the Institute for Astronomy in Cambridge, England, from 1978 to 1982, and an assistant professor at Harvard University from 1980 to 1983. Geller became an astrophysicist with the Smithsonian Astrophysical Observatory in 1983 and a professor of astronomy at Harvard University in 1988.

Since 1980 Geller has collaborated with astronomer John P. Huchra on a large-scale survey of galaxies, using redshifts to measure the galaxies' distance. (A redshift is a shift toward the red or longer-wavelength end of the visible spectrum that increases in proportion to distance.) Cosmologists have long predicted that galaxies are uniformly distributed in space, despite recent evidence of irregularities. Geller and Huchra hypothesized that three-dimensional mapping of galaxies beyond a certain brightness over a large-enough distance—500 million light-years—would confirm the predictions of uniformity. In January 1986 Huchra and Geller published their first results. But instead of the expected distribution, their "slice" of the cosmos (135 degrees wide by 6 degrees thick) showed sheets of galaxies appearing to line the walls of bubblelike empty spaces.

Geller and Huchra's so-called Great Wall is a system of thousands of galaxies arranged across the universe—its full width was indeterminable because it fell off the edges of the survey map. The wall contains about five times the average density of galaxies; but "what's striking," Geller told M. Mitchell Waldrop of Science Research News in 1989, "is how incredibly thin[—fifteen million light-years—the bubble walls] are." Large structures such as the Great Wall pose a problem for astronomers—they are too large to have formed as a result of gravity since the big bang (a cosmic explosion that the universe was born out of and expanded from over time), unless a significant amount of clumpiness was present at the origin of the cosmos. This theory, however, is contradicted by the smoothness of the cosmic microwave background, or "echo" of the big bang. Dark matter, invisible elementary particles left over from the big bang and believed to constitute 90 percent of the mass of the universe, is another possible explanation. But even dark matter may not be capable of producing so large an object as the Great Wall. "There is something fundamentally missing from our understanding of the way things work," Geller told Waldrop. Between January 1986 and November 1989, Geller and Huchra published four maps (including the first), and in each found the same line of galaxies perpendicular to our line of sight. Geller and Huchra's survey will eventually plot about fifteen thousand galaxies.

Geller won a MacArthur fellowship—also known as a "genius award"—in 1990 for her research. She received the Newcomb-Cleveland Prize of the American Academy of Arts and Sciences that same year. In addition to galaxy distributions, Geller is interested in the origin and evolution of galaxies and X-ray astronomy. She is a member of the International Astronomical Union, the American Astronomical Society, and the American Association for the Advancement of Science.