STARSTRUCK
An astronomer scans the bubbles and streamers we call the universe.
Future historians may well pinpoint the present era as a golden age for astronomical endeavors. Driven by advances in both technology and theory, major discoveries are appearing at an accelerating rate. Modern technology has produced equipment— land-based digital detectors and satellite-based X-ray, gammaray, ultraviolet-ray, and infrared detectors—that can obtain pictures of undreamed-of objects at unheard- of light levels. Powerful computers make it possible to conveniently analyze the prodigious amounts of data that the detectors produce. Twentieth-century science gives us new ways of thinking about nature: these ideas include quantum theory for delving into matter's subatomic structure [see the March Syllabus] and general relativity for studying the capacity of gravitational fields of matter to influence spacetime, the overall structure of which we call the universe.
Scientists are merging the new large body of astronomical data with other branches of science—from biology to particle physics—to produce a broader and more general view of the world. The discovery of the previously hidden structure of the universe will doubtless forever change and clarify our perception of our place in the universe—although, as in the past, we may not find out what we expect or wish to learn about ourselves. Astronomy and the other sciences are teaching us that appearances can be deceiving.
Over 50 years ago the American astronomer Edwin Hubble discovered the recession law of the galaxies—that the more distant a galaxy is, the more rapidly it appears to be receding from us. One of the theoretical implications of this recession law is that the expansion of the universe began with the Big Bang, which occurred between ten and 20 billion years ago. Supporting the Big Bang theory is the 1964 finding of the three-degree microwave background radiation that entirely covers the sky and is thought to be a relic of the Big Bang. Further evidence includes nucleosynthesis, the process that scientists believe explains the origin of the elements. Yet recent observations of the distribution and motions of the galaxies suggest that Hubble's picture of the universe may have been too simple.
An important advance in this vein is the discovery of so-called dark matter. Luminous matter at the edge of the observable universe can be seen to consist of the same atomic particles as the earth. However, studies of the internal motions of galaxy clusters- which indicate the distribution of matter within a galaxy—present strong evidence that at least 90 percent of the material in the universe may be dark—only detectable through its gravitational attraction. Astronomers disagree on the composition of dark matter, but generally concur that it is a major clue to the origin and structure of the universe.
The earlier models of the universe that didn't take dark matter into account assumed that matter is everywhere distributed isotropically—that the universe has no edge and is homogeneous. However, observations conducted in the last decade indicate that the closer galaxies define a complicated structure of intertwined streamers or bubbles with mostly empty spaces in between. Furthermore, there is mounting evidence that pieces of these structures partake in large-scale motions that are appreciable fractions of the simple Hubble expansion. Since 1986, a group of astronomers from several institutions nicknamed the Seven Samurai, of which I am a member, have found that our galaxy is headed in the direction of a huge mass called the Great Attractor that is about 300 million light years away in the direction of the southern constellations Hydra and Centaurus. We don't yet know whether this is a rare or common structure, nor do we yet understand all its physical properites. Further investigations are being conducted with the Dartmouth telescopes and elsewhere as we map the distributions of galaxies to ever fainter limits.
The recent discovery of gravitational lensing—the bending of light by gravity—promises to provide a new means of plumbing the distant universe. Although Einstein and others predicted this phenomenon early in this century, extragalactic gravitational lenses have been found only in the last decade. The lens phenomenon occurs when the gravitational pull of a massive object, such as a galaxy, distorts the path of light emitted by a distant quasar—a single immensly powerful but physically small source of light that is probably the most luminous thing in the universe. The phenomenon depends on the amount of matter in the lens, so by studying the lenses researchers can probe the distribution of matter in the universe.
Astronomers offer several explanations of these new observations. Many researchers subscribe to MlT's Alan Guth's inflation scenario, which goes as follows: before the Big Bang, and up to 10-35 of a second afterward, the forces of nature—gravity, electromagnetism, and the atomic-level strong and weak forces—were undifferentiated. The Big Bang separated these forces, triggering the early universe to expand rapidly in a foam of little bubbles, each of which formed a separate universe. Related theories suggest the existence of strongly gravitating cosmic strings threading through the universe, but so far none has been found. Although all present matter, luminous and dark, formed within the first three minutes after the Big Bang, about 500,000 years passed before galaxies began to take shape and the structure of the present universe developed. What happened in between is still unknown.
Cosmologists trying to unlock the mystery of how the present state of the universe occurred are working with theories of cold dark matter, hot dark matter, and so on, as they numerically model the past—and future—evolution of the universe. So far, no consensus has been reached. Through the readings below you can join the explorations.
Stargazer Gary Wegner.
He's an unlikely Samurai, this soft-spoken, rather shy man. Yet astronomer Gary Wegner, the Margaret Anne and Edward Leede '49 Distinguished Professor, is a member of the international "Seven Samurai" astronomy team that is giving a new look to the edges of the universe. And when he turns his telescopes toward the collapsed remnants of stars known as white dwarfs and toward the elliptical galaxies of distant space, the heavens surrender some of their most ancient secrets. Despite the romanticism conjured up by the Samurai image, Wegner's explorations of the universe have a down-to-earth side. "Before a night of observation I panic about making mistakes or having a clear sky. It's probably like an athlete before a football game, worrying about having everything go right," he says. "The observing itself is fairly unexciting. It's a bit like lab work, unromantic. The 12- to 14-hour nights are exhausting." Growing up near Seattle, Wegner revelled in learning the names of stars and reading about astronomy. His prized possession was a telescope. "I always loved Mars," he muses. But, unlike most people who remember an early fascination with the red planet, Wegner's memories display the specificity of a budding astronomer: "In 1954 it was close," he recalls. His career seems to have been set by the stars. After majoring in astronomy at the University of Arizona and earning a doctorate at the University of Washington, Wegner trained his eye on the skies from such far-flung sites as The Australian National University, Oxford University, the South African Astronomical Observatory, and the University of Delaware. Wegner, who came to Dartmouth in 1982, now does most of his stargazing at Kitt Peak in Arizona, where the College shares the MDM Observatory with MIT and the University of Michigan. Revealing a philosophical bent, Wegner draws connections between astronomy and the humanities. "I believe that both science and art—music even—are related," he says. "The mathematical laws of the universe are like a portrait someone can paint—they're a description, not the thing itself. And I find the universe is very beautiful." Karen Endicott
