EXCURSIONS
Tuning In to the Infinite
A cluster of radio telescopes view the edge of space and time
By Tim Folger
Photographs courtesy of NRAO/AUI |
The Very Large Array
Near Socorro, New Mexico
On a high plain 7,000 feet above sea level in central New Mexico is a site as majestic and mysterious as Stonehenge. Like Stonehenge, this is a monument to the heavens, a place where Earth touches the infinite. The monument consists not of megaliths but of 27 dish-shaped radio telescopes that stretch to the horizon, each gleaming white in the clean desert air. All are 94 feet tall, as big around as a baseball infield, and weigh 230 tons apiece, about the same as three fully loaded Boeing 737s. Together they form a giant compound eye with a viewing power equivalent to that of a single dish 22 miles in diameter. And they reveal a cosmos invisible to even the most powerful optical telescopes.
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None of that work would be possible were it not for a rather dated bit of technology: railroad tracks. The tracks, which cut across the approach road to the visitors’ center, appear to lead nowhere. But they are an integral part of the array. Two ungainly 90-ton 24-wheel vehicles shuttle the telescopes to different positions along a Y-shaped pattern of rails with 13-mile-long branches. This mobility allows astronomers to change the resolving power of the entire array, bunching the telescopes together or fanning them out as if they were adjusting a giant zoom lens. When set in the largest configuration, the telescopes have a combined resolution sharp enough to spot a golf ball 100 miles away.
Just inside the entrance to the small one-story visitors’ center is a striking sample of the array’s power: an image that shows several thousand galaxies, each a small white swirl against a pale blue background. Most of the galaxies in the image lie billions of light-years away, and some of the radio waves now breaking against the tiny shoal called Earth left those galaxies long before the sun was born. These galaxies are well beyond the reach of optical telescopes and would have gone undetected without radio telescopes. Unlike visible light, radio waves can pass through the clouds of gas and dust that obscure much of our galaxy. And unlike optical telescopes, radio telescopes can work in the full light of day, whether it’s cloudy or clear.
Each of the telescopes in the array is machined to perfection—the 82-foot-wide aluminum dishes vary from an ideal parabola by less than 20 thousandths of an inch. Motors inside the telescopes power cryogenic pumps and emit a monotonous hum. The electronics must be cooled to –432 degrees Fahrenheit to reduce heat that would blot out the tenuous radio signals of faraway stars. The humming pumps and the pristine beauty of the dish somehow seem reassuring, rare evidence that humanity can sometimes get it just right. Whatever other dubious legacies we may leave our descendants—an ever-warmer globe, too many descendants—perhaps the Very Large Array will remind them that we had at least a few noble aspirations.
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