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Even the powerful W.M. Keck Telescope (co-owned by the University of California, NASA and Caltech), is not immune from the phenomenon. Unlike other large telescopes, the Keck instrument is segmented, made from 36 hexagonal mirrors that line up through an active control system creating, at infrared wavelengths, the appearance of a monolithic piece of glass. "With this telescope, we gain both the ability to see much fainter things and the ability to see them in greater detail," says Ghez, who was originally attracted to UCLA by the opportunity to have access to the Keck. But while most astronomers want to view objects farther and farther away—to learn about the evolution of our universe, for example—Ghez is more interested in seeing the finer details of the objects. And she was determined to find a way. One way Ghez corrected for image degradation was by taking rapid-fire snapshots. "You work out the timescale on which the atmosphere is introducing the errors," she explains. In Ghez's domain of infrared astronomy, that scale is one every 100 milliseconds. By taking and saving pictures at that interval and employing a variety of interferometric and deconvolution techniques, Ghez produced diffraction-limited images. Using these techniques on the world-class Keck Telescope, she secured images with the highest spatial resolution ever seen from ground or space. The breakthrough led Ghez to dramatic discoveries in two fields where muddied pictures had previously stymied researchers: star formation and black holes. With the aid of resolution techniques, Ghez recently found that, contrary to prior assumptions, most stars form with a companion star, located at distances smaller than that of our solar system. Theories on star formation have typically been based on single-star systems such as our own, despite the fact that in our solar neighborhood, about half of the middle-aged stars have |
companions. Many astronomers believed these stars had begun solo and then, by the process of capture, had become binary later in life. The issue couldn't be settled by traditional imaging since the closest star formations are approximately 450 light years away—beyond the reach of traditional methods. Ghez employed her new technique to look at young stars, anticipating she'd find either no binaries, meaning the capture theory was correct, or the same proportion found in middle-aged stars, suggesting companions emerge in the process of star formation. Instead, she found twice as many companions in the younger stars. The reverberations of the discovery were immediate. For one thing, "this suggests there might not be as many planets as one might otherwise think," observes Ghez. Ghez is pursuing several theories to explain the contradiction, each with far-reaching implications on planet formation. At the same time, she is studying the effects of binary stars on planet formation itself. "We want to know whether the close companion stars are going to destroy the discs around these young stars, which are believed to be the birth sites of planets," Ghez explains. Ghez's diffraction-limited imaging at Keck has also broken the impasse on a question that has tantalized scientists for years: whether a massive black hole lies at the center of our galaxy. Astronomers have demonstrated that a central, dark mass exists in so-called active galaxies, explaining the powerful outflows of energy that emerge from these galactic centers. Could the same phenomenon—only in dormant form—be present in "normal" galaxies such as our own? For Ghez, it's simply a matter of mapping mass distribution, using the stars in the center of the galaxy as "test particles" to determine mass of material interior in its orbit. "The key is to prove that there's a lot of mass in a very small volume," she observes. But while the experiment is conceptually simple, collecting the images is anything but. "It's so crowded at the center of our galaxy, stars will blur together if you don't have high-resolution imaging," she points out. But using her techniques, Ghez indeed found evidence of a massive black hole in our galactic center that she says is stronger than previous evidence gleaned from active galaxies. "We can probably conclude now that the majority of galaxies have central black holes," she says. "And we're left with the question of why ours is so quiet." Quiet, maybe. But if Ghez has a say, it will no longer be a mystery. —D.G. |
 Vision
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rom the time she was a graduate student, UCLA astronomer Andrea Ghez dedicated herself to solving one of the biggest problems plaguing astronomers: Atmospheric turbulence seriously distorts the resolution of images obtained by even the most powerful ground-based telescopes in the world. "It's like looking at something at the bottom of a pond," says Ghez. "The wave front is perturbed, which blurs the pictures."
