Into the Cosmos / High-frequency radio signals offer a new way to see deeper into space BY: By Robert Cooke. STAFF WRITER EDITION: ALL EDITIONS SECTION: Discovery DATE: 02-01-2000 C03 EVERY FEW YEARS astronomers get to open a new window that offers a fresh, exciting-and sometimes surprising-view of the universe. Now it is happening again. Having explored the skies for years first by looking at ordinary light, then scanning for radio waves, infrared light, ultraviolet light, gamma rays and X-rays, astronomers have now begun examining the heavens through the so-called "terahertz waveband." This terahertz part of the spectrum is described as radio signals of about 1 million times higher frequency than ordinary AM radio signals. This part of the electromagnetic spectrum offers a new way to study the "molecular fingerprints" of the huge clouds of dust and gas adrift in space among the stars. Using an exotic-sounding new detecting instrument, called a "superconducting hot- electron bolometer," the astronomers will be seeking clues to the physical conditions that exist in the interstellar clouds, "a regime that is very difficult to probe," said astrophysicist David Wilner of the Harvard/Smithsonian Center for Astrophysics in Cambridge, Mass. The new observations-which analyze radio waves to determine what chemicals are their source, rather than taking actual pictures-are picked up via a big radio telescope in Arizona. The astronomers expect to examine star-forming regions where brand new stars are being born, as well as the cold clouds of dust and gas millions of light years away. "Very little has been done in this part of the spectrum, so anything you do is interesting," said astronomer Tom Wilson of the University of Arizona. "It's just easier to find interesting items" when so little observing has been done at new wavelengths. "We're basically looking for the beginnings of stars and how they form, and indirectly for planets, of course. That's the really interesting thing," Wilson said. Looking at terahertz signals has become possible, because researchers at several institutions teamed up to build the new detecting instrument, which "sees" the shortest wavelength radio signals ever used in astronomy. They've only just begun testing the bolometer but have already found carbon monoxide gas glowing energetically in the Orion Molecular Cloud. The first attempt at observations came on Jan. 7, when atmospheric conditions happened to be just right. The "terahertz" region is difficult to see, because water vapor in the Earth's atmosphere tends to block these shorter-wavelength radio signals. That's why the new detector has been mounted on a very accurately constructed, 30-yard-wide radio dish antenna, a radio telescope, sitting atop Mt. Graham in Arizona. At that 10,720-foot altitude, the telescope is above much of the atmosphere. Also, Mt. Graham is in a desert region where the air tends to be relatively dry. The detector, the bolometer, is basically an AM radio that is operating at extraordinarily high frequencies. It relies on an unusual material, an ultracold thin foil of niobium nitride, which picks up the signals coming from far away in space. For observations, Wilson said, a flask of liquid helium-which is close to absolute zero (minus 459.67 degrees)-is poured into the receiving instrument. One such loading is good for about 18 hours of observing, Wilson said. The pioneering new instrument was developed by researchers at the astrophysics center in Cambridge and at the Moscow State Pedagogical University in Russia. Such innovations opening new windows in the sky have been important in the history of astronomy. The dynamic processes going on inside stars and in the interstellar debris all emit signals at different wavelengths. A major problem that has hampered generations of astronomers has come from the fact that many signals, such as infrared and ultraviolet light, do not penetrate Earth's atmosphere very well, if at all. To get around such problems and begin to see what's actually happening out in space, astronomers first resorted to balloons carrying telescopes to high altitude. Then, with the dawning of the space age, increasingly large and complex satellites have been used for making such observations. The best known, of course, is the recently refurbished Hubble Space Telescope, which has returned some of the most spectacular pictures of the sky ever seen. Because satellites orbit above the Earth's atmosphere, there is no interference from atmospheric movements and the signal-absorbing water vapor. So the satellites have been enormously successful at opening the heavens to view. Unfortunately, satellites are very, very expensive to launch into space. And they are often short-lived, compared to ground-based telescopes. So even as satellite usage has expanded, constant efforts have been made to tweak existing telescopes to squeeze out more capability. Development of the terahertz detector is one such attempt. According to Wilner, this terahertz waveband is "kind of the last little bit that we'll be able to see from the surface of the Earth." Even then, it generally will have to be done from high, dry sites, he said. Over the past half century, because new observing techniques and instruments have been developed, the science of astronomy has been completely revolutionized. Although the twinkling stars and wandering planets were once considered a stable and serene system, it is now very clear that the universe is actually an extremely violent place, full of exploding stars, colliding galaxies and star-gobbling black holes. ILLUSTRATION/PHOTO: Photo - This radio telescope, atop Mt. Graham in Arizona, can detect the "terahertz" radio wavelengths. KEYWORDS: ASTRONOMY.RADIO.SPACE.