A powerful X-ray telescope successfully tested by University of Colorado at Boulder and NASA scientists is expected to exceed the resolution of the Hubble Space Telescope by 300,000 times, allowing astrophysicists to peer down the mouths of voracious black holes.
Developed by a CU/NASA team led by Professor Webster Cash of CU’s astrophysical and planetary sciences department, the new telescope design is considered the largest leap in the 40-year-old field of X-ray astronomy. The instrument should be able to detect an object the size of a Frisbee on the sun, which is roughly 93 million miles away, said Cash, also a researcher at CU-Boulder’s Center for Astrophysics and Space Astronomy.
"A million-fold increase in X-ray resolution over today’s instruments will make objects in distant stellar systems appear as if they are here in our own solar system," said Cash. "We will see the discs of stars, image the formation of astrophysical jets and watch blobs of matter spiral into black holes."
A paper on the subject by Cash, CU-Boulder Research Associates Ann Shipley and Steve Osterman of CASA and astrophysicist Marshall Joy of NASA’s Marshall Space Flight Center in Huntsville, Ala., will appear in the Sept. 14 issue of Nature.
The human eye can resolve objects in detail as fine as 1 "arc-minute," or 60 arc-seconds, said Cash. By the mid-20th century, advanced telescopes were resolving images to 1 arc-second -- about the size of a dime seen from two miles away. Hubble increased that resolution 10-fold, to about .1 arc-second.
The advent of radio telescopes has allowed astronomers to resolve images as fine as .001 arc-seconds -- as if the observer were 100,000 times closer to the object -- although the objects are rather dim and diffuse, said Cash. The resolution of the new X-ray telescope will be about 3,000 times better than the most powerful radio telescopes, which -- like the new CU/NASA X-ray telescope -- combine signals from different mirrors using a technique called interferometry to achieve much sharper images.
"A visible-light telescope with the resolution of this newly designed X-ray telescope could be used to count the hairs on an astronaut’s head while she was standing on the moon," he said. "This new telescope has the potential to resolve the ‘event horizon’ of a supermassive black hole in the center of our galaxy or a nearby galaxy."
Nicholas White of the High-Energy Physics program at NASA’s Goddard Space Flight Center, who authored a News and Views article in the same issue of Nature, wrote that Cash’s design "will make it easier than previously thought to obtain a black hole image." The X-ray band of the spectrum is the dominant radiation around black holes.
"Aside from satisfying our intellectual curiosity as to what a black hole looks like, this advance will allow us to test predictions of Einstein’s Theory of General Relativity under the most extreme gravity fields known," wrote White.
Interferometry involves combining light collected by multiple telescope mirrors to essentially create a much larger telescope, said Cash. While some ground-based radio telescopes working in concert are located thousands of miles apart, Cash and his team used a tabletop prototype at Marshall Space Flight Center that included four flat mirrors.
The two sets of mirrors mixed the "wavefronts" of the X-rays, causing them to cross and create "interference fringes," said Cash. The fringes, which are amplified recombinations of the beams, produce much sharper images -- much the way sound waves can be combined to amplify music.
The new X-ray telescope, which has been funded for study with about $750,000 from NASA to date, is under serious consideration for two future NASA missions tentatively set for launch after 2010. The first would be MAXIM Pathfinder Mission, which would test X-ray interferometry in space using a single spacecraft toting multiple telescope mirrors and a single detector.
The follow-up mission, MAXIM, would entail a fleet of up to 33 tiny spacecraft flying in precise formation, followed some 300 miles behind by a spacecraft containing the detector to gather and combine the light from each telescope.
The MAXIM mission could produce images 3 million times sharper than the images produced by the Chandra satellite, the wildly successful NASA X-ray observatory launched in 1999. MAXIM could conceivably image the corona of nearby stars and the discs of distant stars that now are seen only as points of light.
"This new breed of telescope has the capability of bringing distant objects in the universe to our doorstep," said Cash.
For more information on MAXIM on the Web, go to http://maxim.gsfc.nasa.gov. For additional information on X-ray interferometry, go to http://casa.colorado.edu/~wcash/interf/Interfere.htm .
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