Scientists have designed and successfully tested a new type of X-ray telescope that, when fully developed and placed in orbit, may capture the first images of a black hole and resolve details of nearby stars as clearly as we see our own Sun today. The report is published in the September 14 issue of Nature.
The X-ray telescope designed by University of Colorado and NASA has the potential of providing resolution a thousand times sharper than the finest images available today in any wavelength and a million times better than what current X-ray telescopes can muster. In orbit, such an instrument could resolve a region the size of a dinner plate on the surface of the Sun. The telescope employs a technique called interferometry, a process of coupling two or more telescopes together to synthetically build an aperture equal to the separation of the telescopes.
"Through the power of ultra-high resolution, we could journey to distant places without need for a warp drive," said Dr. Webster Cash, a professor at University of Colorado and lead author on the Nature article. "This new approach allows X-ray astronomers to essentially jump from telescopes with resolution no finer than what an amateur uses in the backyard to an observatory far more precise than Hubble."
X-ray telescopes are essential for studying black holes up close, said Dr. Cash, because the X-ray band is the dominant radiation in the region directly surrounding these strange objects. X rays can also travel through the dusty Milky Way galaxy in ways that optical light cannot. X-ray telescopes must be placed in orbit, for celestial X rays do not penetrate the Earth's atmosphere.
Dr. Cash and his colleagues have achieved 100 milliarcsecond resolution (similar to Hubble) in the laboratory with their X-ray interferometer. This is a five-fold improvement over the best conventional X-ray telescopes, which achieve 500 milliarcsecond resolution.
This interferometry design is currently under study at Goddard Space Flight Center in Greenbelt, Md., for two proposed NASA missions with the ultimate goal of imaging a black hole. MAXIM, the Microarcsecond X-ray Imaging Mission, could achieve 100-nanoarcsecond resolution and would entail a fleet of spacecraft with separate optics flying in precise formation. The MAXIM Pathfinder would be a smaller mission with all the X-ray optics on one spacecraft, achieving 100-microarcsecond resolution. These interferometerswould complement, not replace, large area X-ray telescopes also planned for the future.
With 100 microarcsecond resolution, astronomers could image the coronae of nearby stars, seeing the actual disks of other stars which appear now only as points of light. With 100 nanoarcsecond resolution, astronomers could attain one of astronomy's ultimate goals -- imaging a black hole. (It is a thousand-fold increase in each jump from "milli" to "micro" to "nano".)
"Black holes hold an almost mythical attraction," said Dr. Nicholas White, head of Goddard's Laboratory for High Energy Astrophysics. "Compelling evidence that black holes exist has come from observations of their gravitational effect on nearby objects, but the ultimate proof is yet to come -- a direct image of the 'black dot'. The X-ray interferometer may take us there."
Interferometry is a common practice in radio astronomy (e.g. the Very Large Baseline Array) and an emerging technique for optical astronomers (e.g. the Keck Observatory). The technique is similar to the way sound waves can be combined to either cancel each other out (resulting in silence) or amplify the sound. NASA's first orbiting optical interferometer, called the Space Interferometry Mission, is scheduled for launch in 2006.
The Chandra X-ray Observatory, NASA's most powerful X-ray telescope to date, has generated a multitude of major astronomical discoveries in the 15 months since its launch. Chandra achieves its unprecedented 500 milliarcsecond resolution not through interferometry but rather through highly polished and carefully aligned mirrors.
Joining Dr. Cash on the Nature article are Drs. Ann Shipley and Steve Osterman, both at University of Colorado, and Dr. Marshall Joy of NASA's Marshall Space Flight Center in Huntsville, Ala. Testing of the prototype X-ray interferometer took place at NASA-Marshall in 1999.
The proposed MAXIM and Pathfinder missions would launch after 2010.
X-ray Interferometry at CASA
More Images For September 14 Nature Article
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Where Beasts Dwell
Atlanta - January 17, 2000
Culminating 25 years of searching by astronomers, researchers at Massachusetts Institute of Technology say that a faint X-ray source, newly detected by NASA's Chandra X-ray Observatory, may be the long-sought X-ray emission from a known supermassive black hole at the center of our galaxy.
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