A new instrument could spot faintest stars.
Astronomers use charge-coupled devices (CCDs)-light-sensitive semiconductors that register almost every photon that hits them-to catch the scant rays from distant objects. Yet even CCDs fail to perform well at short wavelengths of light. Moreover, they do not record the energy of the photons that hit them, so astronomers must combine them with other optical devices in order to measure spectra.
Now, Anthony Peacock, an astrophysicist at the European Space Agency in Noordwijk, the Netherlands, and his colleagues have built an optical measuring device that they maintain "can overcome the limitations" of conventional CCDs for optical astronomy.
Describing their new "superconducting tunnel junction" (STJ) in the May 9 Nature, the researchers explain that it can detect the position, arrival time, and energy of individual photons whose wavelengths measure as little as 200 to 500 nanometers-from near ultraviolet to visible light. In theory, they say, the current device can detect photons with wavelengths near 20 nm-and with improved superconductors, the wavelength limit could fall as low as 8 nm.
"This is an extremely exciting development," says Charles C. Steidel, an astronomer at the California Institute of Technology in Pasadena. "This new instrument should enable astronomers to obtain images and do spectroscopy simultaneously on every object in their field of view. In the next few years, such devices could make an amazing difference in observational astronomy."
To analyze a celestial object, astronomers first compose images by measuring photon locations and then form spectra from photon energies. These observations demand separate procedures, both of them time-consuming for faint objects.
The new device may enable astronomers "to gather thousands of spectra simultaneously just by taking an image," says Steidel. "For someone studying very faint galaxies, this technology could bring significant gains."
Indeed, the new instrument could "enormously increase the amount of useful information at our disposal," says Francesco Paresce, an astronomer at the European Southern Observatory in Garching, Germany.
"Right now, no instrument can make 3-D panoramic views of the sky and at the same time record the position and time of a photon's arrival, as well as its energy level," says Paresce. The new technology will enable astronomers to analyze large portions of the sky that today must be studied piecemeal, he adds.
"There are distant galaxies whose redshifts we can't measure accurately because bigger telescopes are needed to funnel a small number of photons into the spectrometers," Paresce says. "That precludes us from studying many very faint objects.
"This new instrument," he adds, "could replace many tons of steel in telescopes on land and in space." - R. Lipkin
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|Title Annotation:||'superconducting tunnel junction' overcomes limitations of charge-coupled devices for optical astronomy|
|Article Type:||Brief Article|
|Date:||May 11, 1996|
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