Astronomers lament loss of telescope.

Astronomers lament loss of telescope

A U.S. telescope that had served for 26 years as a leading tool worldwide for studying cosmic sources of radio-frequency signals came crashing down in minutes last week. While officials at the National Radio Astronomy Observatory (NRAO) in Green Bank, W. Va., investigate why the 300-foot-diameter dish collapsed, astronomers say its demise will profoundly limit their capabilities.

"Radio astronomy is going to be pretty tough without it," says Kenneth J. Johnston of the Naval Research Laboratory in Washington, D.C. He says no set of existing instruments can completely fill the void left by the dish failure. Located in a valley shielded from the human-made radio-frequency interference that hampers other facilities, the telescope combined the capacity to observe a wide field of view with the ability to detect very distant objects.

The dish scanned the sky from the North Pole to 19[deg.]S latitude and found radio sources at distances approaching 10 billion light-years. The few radio-telescopes comparable in size to the fallen dish either view less sky or encounter greater interference, says George A. Seielstad, assistant director of NRAO.

Some studies involving the telescope "simply will not be possible with other observatories," Seielstad says. One such recent project, headed by Johnston, detected faint electron clouds around quasars. Perhaps the most noticeable loss associated with the collapse may be fewer discoveries of quasars -- considered the most distant and luminous objects in the universe -- because signals from many are too weak by the time they reach Earth for other telescopes to identify.

Astronomers had planned to use the dish in conjunction with a U.S. satellite scheduled for launch in 1990 (see story, p.340) to detect gamma rays from pulsars, remnant stars of supernova explosions. The two most visible pulsars produce observable gamma rays, and researchers had hoped the telescope's observations of pulsar radio signals might tell them precisely when and where the satellite might look for more pulsars emitting the high-energy radiation. However, other telescopes can provide information good enough to warrant the study, says Carl E. Fichtel of NASA's Goddard Space Flight Center in Greenbelt, Md.

NRAO's Seielstad says a replacement for the dish would cost at least five times as much as the original -- built for $850,000 -- and would take at least two years to construct. The large dish played key roles in many astronomical discoveries, including the finding that gravitational fields of galaxies can act as lenses that bend light (SN: 11/21/87, p.326).