The Chandra X-Ray Observatory opens the book on the high-energy universe.
- By James S. Schultz
- Air & Space magazine, March 2002
NASA/SAO/G. Fabbiano et al.
(Page 2 of 3)
With Chandra, the existence of black holes could at least be indirectly proven. Since 2000, the telescope has conducted observations that provide additional detail about black holes. For example, on September 12, 2000, astronomers announced that the observatory had pinpointed near the center of galaxy M82 an apparent black hole that could represent a missing link between smaller stellar black holes and the supermassive variety found at the centers of galaxies. The M82 black hole has the mass of at least 500 suns concentrated into a region about the size of our moon. Such a black hole would require conditions for its creation, such as the collapse of a "hyperstar" or the merger of many smaller black holes.
Chandra's power comes from its ability to make analytical sense of X-rays. Unlike ordinary light, X-rays are absorbed by Earth's atmosphere and thus can be detected only by instruments riding outside it. They are radiated under intense magnetic conditions, from gravitational forces, or in explosive environments. Thus, X-ray astronomers tend to observe those parts of the universe where the most violent events occur: exploding stars known as novas and supernovas, material near the event horizons of black holes, and supermassive black holes in the centers of active galaxies, clusters of galaxies, and extremely distant but powerful quasars. "It's a universe that's very different than what was imagined," says Riccardo Giacconi, who first suggested a Chandra-size orbiting X-ray telescope in the early 1960s. Giacconi is today an astrophysicist at Johns Hopkins University and president of Associated Universities Inc., which manages the multi-facility National Radio Astronomy Observatory. "Objects may be faint and far away, but [with Chandra] it's not a blur or a fog anymore."
Chandra, the product of a collaboration between NASA, the Harvard/Smithsonian Astrophysical Observatory, MIT, Pennsylvania State University, the aerospace company TRW, and a number of other academic, industrial, and commercial partners, has already been used to make many advances, including confirmation that widespread X-rays detected across the entire sky emanate from the collective emissions of single sources like the energetic, black-hole-fueled cores of galaxies, as well as other active galactic regions, such as stellar nurseries in star clusters. It has also given scientists increasingly detailed views of the environments of black holes; enabled the identification of early stages of star formation; and provided the composition of the extremely hot gases expelled during supernova explosions and from the outer layers of stellar atmospheres.
Chandra's journey into space began in 1976, when Harvey Tananbaum, now director of the Chandra X-ray Center, Giacconi, and seven colleagues submitted a proposal to NASA to build a space observatory capable of collecting and analyzing X-ray emissions from distant sources. Given a budge of $2 billion (slimmed down from $6 billion), with annual operating costs of $50 to $60 million, the researchers created an 11,000-pound spacecraft some 46 feet long and, including its solar panels, 65 feet wide. Because Chandra is designed to receive and analyze astronomical X-rays, its interior differs from that of an optical telescope. If X-rays were to hit a mirror head on, they would pass straight through. So Chandra's are cylindrical, angled so that X-rays graze off, are captured, and then are funneled to the observatory's instruments for processing.
One key mystery that analysis of the resulting images may ultimately reveal is the mechanism underlying massive gamma-ray bursts that emanate six to ten billion light-years away from Earth. The orbiting Compton Gamma Ray Observatory studied the phenomena, but scientists are still puzzling over them and hope that examining the bursts in X-ray wavelengths will offer additional insight. Could these occurrences represent two neutron stars colliding and coalescing? Perhaps they're super-supernovas—"hypernovas," as some have called them, the results of the detonation in the early universe of unstable, ultramassive stars 500 to 1,000 times larger than our sun. Or maybe they're an entirely different class of objects to which a name may some day be attached.
No doubt, say scientists, there are other astronomical conundrums that should yield in time to Chandra's observations. "Astronomy involves a lot of different types of physics and chemistry, but you can't just go into the laboratory to validate your theory," says Leon Va Speybroeck, a contributor to the original 1976 study proposing Chandra and today a telescope scientist with the Harvard/Smithsonian Astrophysical Observatory. "Understanding evolves over time. Someone can't do a single experiment and suddenly settle all questions."
Success has bred huge amounts of data, which is stored in two archives in Cambridge and one just south of Boston, where tape backups are transferred and placed in a guarded vault. Each shift, Chandra generates slightly more than 112 megabytes of data: that's 123 gigabytes per year. Astrophysicists are only now beginning to mine that enormous collection, a task that likely will take years. Although Chandra's operational life is officially five years, most of those affiliated with the project believe its instruments could last 15.
Many questions and answers are likely to be forthcoming as researchers schedule approximately 800 observing sessions each year. Objects under scrutiny will range from stars to gas clouds to nebulae in the Milky Way and beyond, as well as neighboring and distant galaxies. Observers want to answer basic questions: How do celestial objects form, mature, and perish? What is their nature? How do they behave? What in their basic form and function reveals the inner workings of the universe?