Black hole survey.Scanning the sky for high-energy X rays, NASA's Swift satellite has completed the first comprehensive census of active supermassive black holes that lie within 400 million light-years of Earth. The study, reported in October at a meeting of the American Astronomical Society The American Astronomical Society (AAS, sometimes pronounced "double-A-S") is a US society of professional astronomers and other interested individuals, headquartered in Washington, DC. in San Francisco San Francisco (săn frănsĭs`kō), city (1990 pop. 723,959), coextensive with San Francisco co., W Calif., on the tip of a peninsula between the Pacific Ocean and San Francisco Bay, which are connected by the strait known as the Golden , found more than 200 supermassive black holes, including several that had been overlooked in previously studied galaxies. Each black hole, millions to billions times as massive as the sun, lurks at the center of a galaxy but in visible light may lie hidden behind thick layers of dust. However, because X rays penetrate the dust, astronomers can detect black holes by looking for Looking for In the context of general equities, this describing a buy interest in which a dealer is asked to offer stock, often involving a capital commitment. Antithesis of in touch with. the energetic X rays emitted by the gas swirling around and into them. Dormant black holes, like the one at the center of the Milky Way Milky Way, the galaxy of which the sun and solar system are a part, seen as a broad band of light arching across the night sky from horizon to horizon; if not blocked by the horizon, it would be seen as a circle around the entire sky. , emit too little radiation to be part of the new census. The Swift satellite was built to record gamma-ray bursts, the most energetic explosions in the universe. But between bursts, Swift's Burst Alert Telescope searches the sky for X rays, notes study coauthor Jack Tueller of NASA's Goddard Space Flight Center The Goddard Space Flight Center (GSFC) is a major NASA space research laboratory established on May 1, 1959 as NASA's first space flight center. GSFC employs approximately 10,000 civil servants and contractors, and is located approximately 6.5 miles northeast of Washington, D.C. in Greenbelt, Md. The Swift study builds upon X-ray observations made by the European Space Agency's INTEGRAL satellite and NASA's Chandra X-ray Observatory Chandra X-ray Observatory U.S. X-ray space telescope. It was named after astrophysicist Subrahmanyan Chandrasekhar and was launched into orbit in 1999. Its mirror, with an aperture of 1.2 m (4 ft) and a focal length of 10 m (33 ft), produces unprecedented resolution. . INTEGRAL was limited to looking for supermassive black holes in galaxies in the plane of the Milky Way, while Chandra, sensitive to lower-energy X rays than Swift is, could find only more-luminous black holes.--R.C. |
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