What is the biggest thing you can think of? The Earth? The Sun? The Milky Way galaxy? Over the centuries, humans have gradually expanded their conception of “big,” as they have come to realize the awesome distances that our universe encompasses.

Back in the 11th century, St. Anselm proposed one answer. God, he wrote, was “that being than which nothing greater can be conceived.” But if you disqualify God (not a physical entity) or the universe itself (too tautologous) as answers, it may seem as if there cannot be a largest object in the universe. Whatever you nominate, the Next Big Thing will come along to top it.

But astronomer Sandra Faber has an answer that she says you can’t beat. In 1986, she helped discover what is still the largest structure known to man: the Great Attractor, a massive supercluster of galaxies (that is, a cluster of galaxy clusters) spanning some 450 million light years in the southern sky. There is good reason to believe we will never discover anything larger because the Great Attractor’s dimensions were set by the primordial fluctuations of matter density in the universe, shortly after the Big Bang. Although its components are not gravitationally bound (and, therefore, will someday fly apart), it became a distinct structure during the early universe because it did not expand as much as similar-sized regions of average density.

“Clustering proceeds only as long as the density of the universe approaches closure density,” Faber says, referring to the idea that the expanding universe could reverse direction and collapse if there were enough matter to allow gravity to stop or “close” the expansion. “Once you fall below that density, you’re stuck with whatever structures have already formed—nothing more can form. We now think that we’re in a universe that had close to closure density a long time ago but which is entering a phase where repulsive gravity is blowing everything apart. There’s been a shutdown of clustering as a result—that’s why we think we’ve found the end of greatness.”

For many astronomers, the discovery of the Great Attractor might have been the crowning moment of a career. But for Faber, it is only the beginning of a list of equally impressive accomplishments, which led to her recognition last year as one of Discover Magazine’s 50 most influential women of science. She helped plan the Keck telescope in Hawaii, with its revolutionary design that integrates 36 separate mirrors into one smoothly functioning device. She designed the Deep Extragalactic Imaging Multi-Object Spectrograph (DEIMOS), an attachment to the Keck telescope that lets astronomers gather high-quality spectra from more than 100 galaxies at a time. And in 1990, she helped to craft a plan to repair the troubled Hubble Space Telescope with a rebuilt wide-field camera that has since taken so many stunning pictures of the deep universe.

According to her colleague Joel Primack of the University of California at Santa Cruz, it’s difficult to fit Faber’s work into a sound bite because she has done so many things so well. “There are three areas that an astronomer can work in. Sandy is one of the extremely rare group who’s a leader in all three,” Primack says. “The first is theory, and she wrote a really influential paper on cold dark matter. The second is observation, which is what she’s most known for. The third is building major instruments, and she has now built one of the premier instruments in astronomy, which gives us the data in one night that we used to be able to collect in three years.”

When Faber arrived at Swarthmore 41 years ago, she says, it felt like coming home. “Even though I went to an excellent high school, I was a science nerd,” she says. “It was even worse for me because I was a girl.” But at Swarthmore, she instantly felt as if she fit in. “It had a big effect on my personality right away. I met my husband at Swarthmore. I went from feeling negative about the human race to feeling positive. It taught me to like my peers.”

Swarthmore also gave her a flying start on her career in astronomy. She majored in physics and worked at the Sproul Observatory, which had a long tradition of research. (In fact, she and Andrew Faber ’67 were married at the Friends Meetinghouse by the campus’s night watchman. How did she come to know him? “When you’re in astronomy, you’re up a lot at night,” she explains.) She grew especially close to Professor of Astronomy Peter Van de Kamp, who invited her into his home and once asked her to take care of his ailing wife when he was out of town. And, as chair of the student-run colloquium committee, she also got the chance to meet top researchers in physics and astronomy. “It was Shangri-La for me,” she says.

After Swarthmore, graduate school at Harvard was a “big letdown” for the budding scientist. Fortunately, she didn’t have to stay there for long because Andrew moved to Washington, D.C., and she went with him. She managed her way into the Department of Terrestrial Magnetism, a laboratory at the Carnegie Institute of Washington that, despite its name, did all sorts of astronomical research. That was where Faber embarked on her life’s work, the study of galaxies. “It was the obvious choice,” she says. “Astronomers had spent the previous 20 or 30 years figuring out how stars worked. Galaxies were the next step up on the scale of the cosmos.”

During the next decade, first at Carnegie and then at UC–Santa Cruz (the first and only postdoctoral job she has had), Faber built a reputation as an expert on elliptical galaxies. These galaxies are somewhat less photogenic than spirals such as the Milky Way and the Andromeda Galaxy. Faber describes them as “big, fluffy balls of stars.” But because they are less highly structured, she thought they might also be simpler to understand. And, in fact, Faber discovered the first empirical laws about them, such as the “Faber-Jackson law” (named after herself and co-author/graduate student Robert Jackson). It says that stars orbit faster in larger, brighter elliptical galaxies because, even though the net rotation of the system is small, such galaxies are, says Faber, “clouds of stars that orbit every which way.”

However, there was a problem with the Faber-Jackson law. The relation wasn’t tight—there was still quite a bit of variation in the rotational velocities that couldn’t be explained by the galaxy’s luminosity. In the roundabout, illogical way that is typical of science, this discrepancy led to the completely unexpected discovery of the Great Attractor.

Thinking that the problem was a simple lack of data (because only a couple dozen elliptical galaxies had been studied), Faber assembled a team of seven astronomers in the early 1980s to do a systematic galaxy survey. They set out to measure every conceivable parameter—mass, luminosity, size, “metallicity” (the proportion of elements heavier than helium)—in 300 galaxies. As the data came in, they bumped over and over into an inconsistency that took them years to identify: The distances to the galaxies were wrong.

Ever since Edwin Hubble discovered in the 1920s that the universe was expanding, astronomers have used that fact as a convenient way to measure distances. According to Hubble, the expansion of the universe was uniform, so that distant galaxies are moving away from us faster than nearby galaxies. Surprisingly, this speed of recession is one of the easiest things to measure in a distant object because it produces a “redshift,” a displacement of the entire spectrum of the galaxy toward longer (and redder) wavelengths. Over the years, therefore, astronomers had unconsciously come to use redshift as a proxy for distance.

But for nearby galaxies—those within 100 million light years of us—Faber and her colleagues (who became known as the “Seven Samurai”) discovered that the “Hubble flow” was not uniform. Instead, the flow matched what you would expect if the cluster of galaxies that the Milky Way belongs to (the Local Cluster) was just a suburb of an immense megalopolis, which they named the Great Attractor. It turned out that all of the galaxies in our neighborhood are being pulled toward the Great Attractor, and the ones that are closer to it are being pulled faster.

It was a discovery whose importance far outstripped the problem it was originally intended to solve. It did tidy up the Faber-Jackson relation because the inaccurate distances had created a corresponding inaccuracy in the inferred luminosity of the galaxies. But what grabbed the headlines was that Edwin Hubble’s picture of uniform expansion was wrong—even at the coarsest scale. The universe has ripples in it.

In the early 1990s, these ripples were first seen by the Cosmic Background Explorer (COBE) satellite, which succeeded in making an image of fluctuations in the cosmic microwave background radiation that fills the sky. (The COBE project was led by John Mather ’68.) This uneven—or “anisotropic”—radiation is a snapshot of how the universe looked when space first became transparent, some 300,000 years after the Big Bang. This year, results from the Wilkinson Microwave Anisotropy Probe provided a much more detailed “baby picture” of the early universe.

The size of the ripples has provided crucial evidence for one of the most provocative theories in modern cosmology—that there is a huge amount of matter in the universe that we cannot see, called “dark matter.” This idea is not one that Faber came up with herself (it was first proposed by Fritz Zwicky, a cosmologist at Caltech, in 1931), but she played a large role in making it respectable.

What is dark matter? It can’t be seen because it is impervious to light, and it can’t be touched because it doesn’t interact perceptibly with ordinary matter. The only thing it does is gravitate, and that—for now—is the only reason we know it exists. And yet, as Faber says, “Space is full of this stuff.” Making a small rectangle with her fingers, she says, “If you look right here, there could be dozens of these things [particles of dark matter, or “weakly interacting massive particles,” as physicists call them] passing through here in a second. And it’s not ‘out there’—it’s right here.” The search for direct evidence of dark matter continues today in particle colliders on Earth, but it began with observations of galaxies.

Since her days with the Seven Samurai, Faber has been drawn more and more into “big science,” with her involvement in the Hubble Space Telescope and Keck Telescope projects. The Space Telescope experience especially taught her the importance of questioning assumptions.

One month after its launch in April 1990, it became apparent that something was wrong with the Space Telescope. It had trouble tracking stars, and measurements of its optical quality were so bad they were off the charts. Faber and former student Jon Holtzman suspected that the problem was spherical aberration, the simplest flaw a telescope can have. “I didn’t know anything about optics, and yet the world’s greatest optical experts were staring at the images and couldn’t make head or tail of them,” she says. “Why? Because they were so horrible. They were looking for some very deep and very fancy reason, and it was right there in front of their eyes.”

Ultimately, Faber and Holtzman did convince the experts by producing simulated images with spherical aberration that matched exactly what they were seeing through the telescope. Meanwhile, another former student, Tod Lauer (whom Faber calls “the savior of the space telescope”) was working out how to compensate for the spherical aberration by reprocessing the images in the computer. “It was like having two telescopes in one,” Faber says. “Fifteen percent of the light was good old sharp space telescope, and 85 percent was like looking through the shower door. The trick was to glom onto the 15 percent that was OK and synthesize almost perfect images.” Lauer’s workaround bought time and maintained public support for the Hubble, allowing it to work effectively until astronauts could install corrective optics during a repair mission in 1993.

Faber learned a lasting lesson from the experience, which has helped her in other large-scale projects. “I am convinced that the only way you can get a good product is to have proper collaboration between scientists and engineers,” she says. “Each mentality by itself is doomed to failure. If you leave scientists in charge of construction, they will try to understand every anomaly, and you will never get done. By the same token, if you leave engineers in charge, they will never get to the bottom of important discrepancies. The project will be on time and under budget, but it won’t work. The failure [of the Hubble Space Telescope] was a failure of the engineering mentality to question.” But she also faults NASA’s management style in the 1980s. “It was a shoot-the-messenger culture—you couldn’t tell the truth,” she says. “There were optical people who strongly suspected the spherical aberration at the time and didn’t say anything.”

Although she enjoyed her forays into the theory of cold dark matter on one hand and basic applied optics on the other, Faber says she has remained first and foremost an observer. The completion of the DEIMOS in Hawaii has allowed her to get back to the work she began her career with, studying the evolution of elliptical galaxies. But she seems just as pleased about the way DEIMOS has facilitated other astronomers’ projects. “This is a workhorse, the single most productive instrument on the Keck telescope,” she says. That is no accident because before DEIMOS was even built, she assembled a “scientific case” for it that included six possible applications.

“There are two philosophies of observing, analogous to two philosophies of cooking,” says Faber, who, incidentally, is an enthusiastic cook. “One is to go to a cookbook, find a recipe, go to the supermarket, and get exactly what you need. The other is to stock up the pantry with an array of quality ingredients and only then ask, what can I cook?”

Faber’s career in the kitchen of science has followed the second philosophy. “I like a well-stocked pantry with fundamental observations and good data,” she says. Using all the ingredients and tools at her disposal, she has served up a career full of delicious ideas.

A former mathematics professor, Dana Mackenzie is now a freelance science journalist whose work appears in such publications as Science, Discover Magazine, and New Scientist. His first book, The Big Splat, or How Our Moon Came to Be, was published by Wiley in April 2003.