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Comment on this article This is the Way the World Ends
Robert Frost and T. S. Eliot speculated about the last days of the cosmos. By examining black holes, a newly formed coalition of Yale physicists and astronomers are figuring out whether the fate of the universe is fire or ice, bang or whimper.
February 2003
by Bruce Fellman This is a story about nothing—well, not quite nothing. Armed with powerful new instruments, from giant optical telescopes to sophisticated satellite-born observatories, researchers have discovered that the heavens are densely packed with objects and forces we can’t see with our eyes. But though black holes, dark matter, and a strange new concept called “dark energy” may be out of sight, all play a major role in the origin, evolution, and fate of the known and, at present, unknown universe. At Yale, this dark side of the cosmos has become the domain of a newly formed coalition of astronomers and physicists. “Researchers have made truly mind-boggling discoveries in the past decade,” says astrophysicist Meg Urry, who, until she joined the faculty in 2001, had directed the office that selected which scientists would be granted viewing time on the Hubble Space Telescope. Urry, the first woman to be tenured in the physics department here, came to the University to head the Yale Center for Astronomy and Astrophysics. Inaugurated on July 1, 2001, the Center helps physics and astronomy, which in the past had followed different academic paths, to work closer together. “There are a lot of synergies possible,” says Urry, who studies the behavior of the enormous black holes that appear to lie at the heart of every major galaxy, including our own Milky Way. “Physicists, for example, are very good at building the kinds of instruments that astronomers like to use, and astronomers have an understanding of the universe that is critical to developing experiments that can enable us to make sense of recent discoveries.” Physicist Charles Baltay, whose research involved building detectors to find some of the fundamental building blocks of matter, was one of the first professors at Yale to begin bridging the intellectual divide. As is typical here, the disciplines came together over food. “This really started in the early 1990s with Chinese lunches I shared with astronomer Charles Bailyn,” says Baltay. At that time, Baltay had been perfecting the development of “charge-coupled devices,” or CCDs. The image-capturing heart of digital cameras, CCDs have revolutionized astronomy, where the devices are used to capture the light from even the faintest of stars and turn it into a digital form that computers can handle. But as the two scientists dined together, the conversation, Baltay recalls, was less about CCDs and more about exciting developments in astronomy. “I was fascinated by the field, and what got me going was intellectual curiosity,” says Baltay. “The age and future of the universe had once been solely the concern of departments of religious studies, but we were now attempting to measure it. This was brand new science, and I was hooked.” Perhaps nothing more than stimulating conversations would have come out of these meetings, but ten years ago, the physics community experienced what for many scientists was a career-altering, even ending, disaster. Understanding how matter and, by extension, the universe was put together required a series of ever-more-powerful atom smashers, and the U.S. Congress had always been willing to foot the bill to build and operate these ever-more-expensive research tools. But in 1993, the federal government pulled the plug on the multibillion-dollar Superconducting Supercollider, which was already under construction in Texas, and without the SSC, it appeared that many burning questions were neither going to be asked nor resolved. Some physicists turned their attention to problems that could be resolved with existing tools; others left the field to parlay their number-crunching skills into careers on Wall Street. Baltay followed his intellectual curiosity and became an astrophysicist. In short order the Eugene Higgins Professor of Physics and Astronomy used his CCD expertise to build a sensitive wide-angle camera—the first major piece of astronomical equipment crafted at Yale since the early 1960s—entered into a collaboration with the national observatory in Venezuela, and began to search the heavens for quasars, curious objects that might reveal the workings of the universe. In turning to astrophysics, Baltay closed at Yale what many would consider a very old research circle. Ever since their earliest days, the two sciences have been linked: Astronomers, peering through telescopes, would discover a new object; physicists, quill pens in hand, would try to determine, then predict, the object’s movement in the sky. “Both physics and astronomy are fundamentally observational sciences,” notes Baltay. “Progress in each endeavor depends on the researcher’s ability to observe.” Two recent observations have brought the two disciplines—and departments—closer than ever. The first was the realization that the planets, stars, galaxies, and the rest of the universe astronomers could see made up only about 10 percent of all matter. If nine-tenths of the total mass of the cosmos is in the form of “dark matter,” as the stuff was dubbed, then particle physicists like Baltay needed to get back to the black boards to attempt to explain the nature of this material. Even more perplexing was the finding that the universe is misbehaving. About 15 billion years ago, according to 20th-century scientific discoveries that flow out of the relativity theories of Albert Einstein, the universe we inhabit came into being as a result of a still unexplainable act of cosmic creation known as the Big Bang. Ever since that instant, the cosmos has been expanding, but because of the dominant force of gravity, one theory suggested that the expansion would slow, and maybe reverse, with all of creation eventually coming back together in a Big Crunch. (An alternative posited that the expansion would go on forever until an ending dubbed the Big Chill.) In 1998, however, astronomers attempting to measure the cosmic slowdown discovered something entirely unexpected: The expansion rate is accelerating. Some mysterious force that could overcome gravity appears to be propelling everything outward at an ever-increasing speed. “All of a sudden, there are many fundamental things we can’t explain,” says Baltay. Physicists didn’t have the atom smashers they desired, but those investigators who turned to the astronomy community learned they had something just as good. “Celestial objects could be laboratories for physics,” says Charles Bailyn. “Great data can come from the sky.” But obtaining data can prove tricky. In astronomy, there is a disparity between supply and demand. Large, ground-based observatories come with multimillion-dollar price tags, and even though the University opened a fine modern facility in 1994 on Kitt Peak in Arizona, the WIYN telescope, the result of a collaboration between the University of Wisconsin, Indiana University, Yale, and the National Optical Astronomy Observatories, rarely provides enough viewing time for everyone. The situation is worse if the objects an investigator wants to study require one of the world’s largest telescopes—the mirror of the WIYN is 3.5 meters across; the mirror of the much more powerful Keck Telescope in Hawaii is 10 meters across—or an orbiting observatory like the Hubble Space Telescope. There’s always a keen scientific competition for time on these precious resources, and if it’s your turn and the weather is cloudy or a satellite develops a mechanical difficulty, an entire research project may have to wait until next year. There are, however, creative ways around the supply problem. One involves a collaboration with Chile, a country whose Andean peaks are perfect for large telescopes. However, Chile lacks graduate training in astronomy, so, in exchange for viewing time, Yale is bringing Chilean students to New Haven while it helps the country develop doctoral-level programs. “This is a tremendous bargain for us,” says Urry. “At a discount, we get facilities that allow us to stay at the forefront of astronomical research.” Charles Bailyn, who chairs the astronomy department, has worked out another strategy, which also involves Chile. “One of the best things about astronomy is that bigger, better instruments don’t make older, smaller telescopes obsolete,” says Bailyn. “You don’t necessarily need brute force—you can win by being clever.” Bailyn is putting together scopes that had been destined for mothballs into a powerful array known as SMARTS. The Small and Moderate Aperture Research Telescope System is based at Cerro Tololo, an observatory complex in the Andes, and the SMARTS network is designed to enable astronomers to take nightly looks at fairly bright objects over long periods. “Most viewing time on the large telescopes is allocated by the night, and you rarely get more than a few nights in a row,” says Bailyn. “But we’re able to do continuous monitoring over weeks or months.” The original scope in the SMARTS group is Yale’s one-meter workhorse that had been in Bethany, Connecticut. Because of light pollution, serious astronomy close to home was impossible, so Yale sent the scope, tiny by modern standards, to the dark skies of the Southern Hemisphere, and there, in collaboration with the Association of Universities for Research in Astronomy, the Lisbon (Portugal) University, and Ohio State, astronomers began keeping tabs on intriguing objects. Recently, other neglected, similar-size scopes have been put to work scanning the heavens. Of current interest to the astronomer is 4U1543-47. Invisible to the naked eye, the star has an unusual behavior that is apparent only when it is viewed every night for a long time. Unremarkable for much of its life, 4U1543-47 will, every so often, grow much brighter. The increase is even more impressive to the “eyes” of orbiting observatories sensitive to X-rays. “This star can suddenly become one of the brightest things in the X-ray sky,” says Bailyn. Such a massive outburst of energy is hard to explain with conventional theories, but after making a series of exquisitely precise measurements, Bailyn thinks he knows what must be powering 4U1543-47. “The star is orbiting a black hole,” says the astronomer. A black hole, once the stuff of science fiction, is the inevitable last stage in the life cycle of stars that are more than three times the mass of the sun at the end of their lives. The energy from nuclear fusion enables a star to keep its shape, but eventually, a star will use up its fuel and collapse. In the case of our sun, the end result is a small object called a white dwarf. If, however, the star winds up 1.4 times as massive as the sun, its last gasp is a collapse in which protons and electrons are squashed together into a tiny object—the diameter is estimated to be 10 miles—called a neutron star. The idea of a dead sun on which each tablespoon of matter would weigh 100 million tons is strange enough, but the finale of a star at least a few times more massive than our sun is almost too bizarre to comprehend. Its collapse creates a minute structure whose gravity is so strong that nothing, not even light, can escape from its grip. In the case of 4U1543-47, its black hole companion will, from time to time, capture material from the star, and at least some of this stuff, just before it vanishes forever, will be converted into bursts of X-ray energy and visible light that Bailyn has been able to detect, monitor, and use to figure out the identity of the hidden partner. While the scientific community is not quite ready to acknowledge the absolute reality of black holes—the object Bailyn studies (and more than a dozen like it) is officially termed a “black hole candidate”—many astronomers use them as key players in the evolution of the universe. For example, Richard Larson, who joined the astronomy department in 1968, suspects that black holes may have developed very early in the history of the cosmos. Indeed, they may even be the “seeds” of later galaxies. Larson is interested in the birth of the first stars. Working with Yale theoretical astrophysicist Paolo Coppi and then-graduate-student Volker Bromm ’00PhD, the scientists developed an astronomical “incubator” that, inside a high-speed computer, has provided a plausible picture of how the universe made the transition from darkness to light. (Bromm’s doctoral dissertation on the subject received the 2002 Robert J. Trumpler Award from the Astronomical Society of the Pacific for research “considered unusually important to astronomy.”) According to their model, about 100 million years after the Big Bang, the first stars, which were made completely of hydrogen and helium, grew from aggregations of matter into objects more than 100 times the mass of the sun. “Massive stars are always short-lived,” says Larson. “They shine so brightly that they quickly run out of fuel.” Their time on the celestial stage is around a few million years—a star like our sun can live for several billion years—and their future, as was the case with Bailyn’s smaller stars, also depends on their size. Those somewhere between 100 and 250 times the mass of the sun simply explode, a fortuitous end, in that stars are thought to be the cauldrons in which more complex chemicals are created and, in death, liberated for eventual use as the raw materials from which life could evolve. But theory predicts that spent stars more than 250 times the mass of the sun have a very different end in store. They become black holes—but significantly larger ones than the variety Bailyn studies. And in a way, says Larson, “the first stars, though long extinguished, may still be with us.” For those premier stars sat at the most dense collections of matter in the early universe. But when they collapsed, the same physical principle—angular momentum—that keeps the Earth in orbit around the sun prevents these dark cores from dragging the surrounding gas and dust into instant oblivion. In fact, says Urry, “my black holes are really just big, gentle giants.” Because of gravity, the remaining material attracts more stuff, and in time this becomes an increasingly large swirl of matter—a galaxy. Astronomer Robert Zinn has demonstrated that galaxies grow by mergers and acquisitions, and using Baltay’s data, Zinn recently caught our own galaxy, the Milky Way, in the act of capturing one of its smaller neighbors. The assimilation has been benign, but the end game is not always peaceful. “The Milky Way and the Andromeda galaxy, our nearest large galaxy, are approaching one another, and eventually, they’ll start a doomsday dance in which they’ll spiral together,” says Zinn. The end, at least several billion years in the future, will be fiery, as clouds of gas are slammed together and give rise to stars, and untold tons of material, pushed into black holes, become beacons of energy visible across the universe. The result is a quasar—a “supermassive black hole in the midst of a feeding frenzy,” says Urry, who studies their behavior—and it is these objects that Baltay and the Quasar Equatorial Survey Team have sought with telescopes in Venezuela and, currently, with instruments on Mount Palomar in California. Initially, the QUEST goal was to use quasars to establish the age of the cosmos, but the object of the project has evolved recently. Baltay and his colleagues are interested in “lensed” quasars: objects whose light has been turned into two identical images by the gravity of some massive galaxy. In scanning the universe, the scientists hope to find quasars that are bent double by, to the eye, nothing—by an invisible clump of dark matter. Detecting at least some of the “missing” mass of the cosmos would be useful to theorists, but Baltay explains that gravitationally lensed quasars may also help confirm or refute the accelerating universe notion and the “repulsive gravity” that may be hurtling everything towards a chilly finale. “If dark energy proves to be real, then, T.S. Eliot was right,” says Baltay. “The end is a whimper.”  |
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