Margaret Geller first met the stickman in the fall of 1986. While the exact date has faded from her recollection, she remembers the time as midafternoon and her reaction as a kind of euphoria. No one had ever seen the stickman before--at least, not really. Valérie de Lapparent, who was Geller’s graduate student, noticed it but says she was too inexperienced to understand its implication. John Huchra, who was Geller’s collaborator at the Harvard-Smithsonian Center for Astrophysics (cfa), says he took one look at the stickman and assumed he had botched his observations. It took Geller’s eye to recognize the stickman as something real and important.
Geller, Huchra, and De Lapparent had mapped the nearby universe, taking several months to carefully measure the distance to 1,000 galaxies, some as near as 30 million light-years away, others as far as 650 million. De Lapparent had fed the distance and positions of those galaxies into a computer program that printed out a two-dimensional representation of their three-dimensional distribution in the universe. On the printout was this slice of the northern sky, sprinkled with 1,000 distant galaxies, and smack in the middle, says Geller, was this remarkable stickman figure. The distribution of galaxies looked like a child’s drawing of a somewhat bowlegged person. It’s a whimsical name for a grand figure: the stickman extended 500 million light-years across the universe. Its torso was composed of hundreds of galaxies, a massive congregation known to astronomers as the Coma cluster. Its arms were two more sheets of galaxies streaming across the night sky.
The stickman was grand not just in dimension but in destiny. You might even say it changed our understanding of the universe. Until the stickman, the universe appeared to be a smooth and homogeneous place. Astronomers believed that galaxies were distributed at random, although they might occasionally form clusters like Coma containing as many as a thousand or so galaxies like the Milky Way. There was even some evidence that the universe contained at least one enormous void, in the constellation Boötes, which seemed to extend for some 200 million light- years--and other suggestions that galaxies could be found strung out on long filaments. But in 1985 most astronomers assumed these structures were products not of the universe itself but of the methods used to survey it.
Then Geller saw the stickman, which constituted compelling evidence that galaxies were congregating on two-dimensional structures, as though they had condensed out of the cosmic nothingness on the surfaces of invisible bubbles. Indeed, when Geller later wrote up the results of the cfa galaxy survey, she described the distribution of galaxies in the universe as looking like a slice through suds in the kitchen sink. Her metaphor implied that astronomers were mightily confused about how the universe had formed.
The very early universe, around the time of the Big Bang, was a smooth place. We know that because the Big Bang left an imprint: the cosmic background radiation, which is a radiation 3 degrees above absolute zero that pervades the entire universe. That background radiation is considerably smoother than a baby’s behind, and it means the universe, when it was a couple of hundred thousand years old (and maybe even younger), was equally smooth. Now it’s not. It’s full of these enormous two-dimensional structures. Perhaps the most awe-inspiring is one that Geller and Huchra discovered in 1989, known as the Great Wall: a sheet of galaxies extending for at least 500 million light-years, stretching across the entire northern sky. It may indeed be bigger than 500 million light-years, but no one can yet tell.
