OCR Text |
Show I Observatory far exceeds hopes ago, or whether there is enough mass in the universe so that eventually even-tually gravity will halt the expansion and bring the matter back together, thus repeating the cycle of cosmic birth and death. The answer may rest on how much matter there is in the universe. K A the black hole due to its tremendous gravitational force. The process would produce an enormous flow of high-energy radiation in the form of X-rays. By looking for this type of X-ray emission, astronomers now have detected several black hole candidates. can-didates. If black holes are the most difficult to detect, quasars are the most mysterious objects in the celestial "bestiary." Quasars are bright, starlike star-like objects apparently located at the very edge of the visible universe. Although they are about the same size as our solar system, they radiate as much visible light as a thousand galaxies. Until Einstein, however, only three to five quasars were known to emit X-rays. But when Einstein trained its telescope . on some of the areas of the sky where quasars had been identified iden-tified from optical observations, ob-servations, it found more than 200 that were strong X-ray emitters. "We now think," Tananbaum said, "that quasars are among the most important contributors con-tributors to the X-ray sky, which raises all kinds of interesting questions. What powers quasars, where do they fit in with galaxies, have we seen the most distant quasar yet?" In fact, X-ray astronomy is a powerful tool for studying nearly all the interesting questions in astronomy, including the question of whether the universe is open or closed. This question centers on the debate over whether the universe will continue expanding forever, a result of the initial "Big Bang" that created the universe some 10 to 20 billion years At the Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass., X-ray images relayed to Earth by the Einstein Observatory are analyzed with a computer and stored for future reference. F.R. Harnden, Jr. studies X-ray images of the Crab Nebula, the remains of a giant star that exploded in 1054. By MADELEINE JACOBS Smithsonian News Service CAMBRIDGE, Mass. There probably won't be a wake for the deceased, but sometime soon in the next few days or weeks, perhaps even a as you read this scientists here will pay their last respects to a beloved "colleague." Affectionately nicknamed Einstein, the "colleague" is a 7,000-pound 7,000-pound astronomical observatory orbiting the earth 300 miles above its surface. Launched Nov. 13, 1978, the Einstein Observatory has far exceeded its expected one-year lifetime, but now it is about to exhaust the propellant that keeps its unique X-ray telescope pointed in space. Ein- difficult, he knew, but forming actual pictures of them would be another matter altogether. In ordinary telescopes, mirrors and lenses are used to focus the radiation arriving from space to form an image. "But under normal conditions, lenses and mirrors tend to absorb rather than focus X-rays," X-rays," Giacconi explained ex-plained Undaunted by this formidable obstacle, he assembled a team of scientists and engineers and began tackling the problem. The result was a novel set of optics and the first imaging X-ray telescope, a source of considerable pride to the 49-year-old Italian-born-and-educated physicist, who has been dubbed "the man with X-ray vision." star, porh?ps 10 times more massive than our sun, which has entered the final stages of stellar evolution and begun to collapse. In this concept, once the collapse begins, the inexorable force of gravity continues to compact the matter until it is so dense that it is a mere point and nothing, not even light, can escape from its gravitational field hence the name, "black hole." If this model is accurate, ac-curate, scientists could never detect a black hole directly, since detection relies on some kind of radiation emission. A black hole could be. detected indirectly, however, if it were part of a binary system two stars circling each other. Under these conditions, material from the normal star might be sucked into the images are analyzed with a computer and stored for future reference. "When the satellite finally dies," Tananbaum said, "there still will be a wealth of potential surprises and amazement lying in all the information which we haven't yet been able to systematically categorize and analyze. Out of this analysis may come new examples of the pathological 'black beasts' lying in outer space." For now, there are plenty of "beasts" to fascinate and intrigue the hundreds of astronomers and physicists who have used Einstein's facilities as guest observers. For starters, there are the notorious "black holes. According to one theory, a black hole is a "The Einstein' telescope is comparable to the optical sensitivity of the 200-inch telescope on Mount Palomar," Giacconi notes, "which in turn is 10 million times more sensitive than the human eye." This remarkable sensitivity has enabled Einstein's "eyes" to detect X-ray sources one thousand times fainter than any previously observed. The telescope has now completed about 7,000 of 10,000 proposed ob-servatons, ob-servatons, according to Dr. Harvey Tananbaum of the Center for Astrophysics and one of the principal scientists working with Giacconi, who has overall responsibility for the Einstein observation program. Images from the observatory ob-servatory are transmitted tran-smitted to the worldwide satellite-tracking stations of the National Aeronautics and Space Administration, which sponsors the entire Einstein program. From there, the information is relayed to NASA's Goddard Space Flight Center in Maryland and then onward to the Center for Astrophysics where X-ray image of the Crab Nebula reveals a pulsar (bright spot in lower left), which is a rapidly spinning neutron star having a strong magnetic field. stein literally is running out of gas. Like its namesake, however, the Einstein Observatory leaves a legacy that will occupy the thinking of physicists and astronomers for years to come. "The Einstein Observatory Ob-servatory has changed our perspective of astronomy," said Dr. Riccardo Giacconi of the Harvard-Smithsonian Center for Astrophysics. "It provided numerous examples showing that things are different in the universe than they are in the solar system." Indeed, from Einstein's X-ray images, ear-thbound ear-thbound astronomers have gleaned a few view of the heavens. Gone, Giacconi said, is the idea of a universe "filled with majestically rotating plaxies, slowly evolving over billions of years." Instead, Einstein has revealed many details of a dynamic, explosive universe in constant turmoil, a place populated with bizarre and mysterious objects-exploding objects-exploding galaxies, pulsars, black holes, cosmic bursters and those most mysterious of all objects, quasars, located at the very edge of the universe. These celestial members, like the planets and our sun, can only reveal their presence and secrets to astronomers through their characteristic radiation. While many objects emit visible light, radiowaves and other radiation, only the hottest, hot-test, most energetic objects produce most of their radiation in the short wavelength form known as X-rays. The X-rays emitted readily travel the vast interstellar and in-tergalactic in-tergalactic distances separating us from their point of origin, but the earth's atmosphere blocks ground-based astronomers from detecting them. An observatory orbiting or-biting well above the atmosphere is a tidy solution to this problem, a solution Giacconi first recognized . more than 20 years ago. Detecting X-rays from such a satellite would not be |