Scope's face-lift pulls deep space in view
ARECIBO, PUERTO RICO — The world's largest eye on the sky is getting a face-lift that will allow astronomers to do what was once unthinkable: probe large swaths of space more deeply than ever before. Think of it as astronomy's leap from 16th-century mapmaking to early Rand McNally.
If all goes well, scientists could double the number of known pulsars (pulsating stars), discover clouds of gases that failed to create galaxies, and maybe even spot the holy grail of radio astronomy: a pulsar circling a black hole, offering new data on the actual workings of relativity.
These possibilities come courtesy of Arecibo Observatory, here in north central Puerto Rico, the world's largest, most sensitive - and now much improved - radio telescope. Starting in roughly two years, the massive survey of the heavens will not only give the venerable telescope a new mission, it may well change the way many radio astronomers do their work.
"There will be lots of groups that will benefit from these large-scale surveys," says Daniel Altschuler, director of the Arecibo Observatory.
Up to now, most of the research at Arecibo has come from individuals or small teams of scientists, using the telescope for their allotted time. For the new survey work, multiple teams, involving hundreds of scientists with varied research interests, would share the torrent of data spewing from Arecibo's receivers. Astronomers interested in galaxy formation would be working side by side with those searching for pulsars or extraterrestrial life.
Already last month, groups of astronomers met here to take the first crack at developing ground rules for how they will cooperate. The scientists need to figure out not only where the telescope will look first but also how long it will stare at particular locations and who will get credit for the new discoveries they're almost certain to find. While such large groups already collaborate in some fields, such as high-energy particle physics, the idea remains relatively novel in radio astronomy.
"I think we're seeing the de-Balkanization of pulsar research," says Tom Bania, an astronomy professor at Boston University.
Unlike optical telescopes, which capture visible light, radio telescopes capture radio waves emitted in various ways from objects in space. These telescopes are built large because the cosmic signals are so weak. All the signals collected by all Earth's radio telescopes in the past 60 years amounts to no more than the energy released when a few raindrops hit the ground.
Even by radio-telescope standards, however, Arecibo stands out as a physical giant. Its collector - a spherical dish 1,000 feet wide suspended above a sinkhole in the Puerto Rican limestone hills - is nine times bigger than the world's next largest radio telescope. The dish covers 18 acres, the equivalent of 26 football fields or 10 billion bowls of cornflakes.
Because of its size and sensitivity, the behemoth has mapped the moon, Venus, Mars, and the rings of Saturn. It discovered the first pair of pulsars orbiting each other, the first Earth-like planets outside the solar system, the rotational speed of Mercury (much faster than originally thought), and the size of galaxies (much larger than thought).
"Arecibo is a discovery-type instrument," says Riccardo Giovanelli, professor of astronomy at Cornell University in Ithaca, N.Y. "It does stumble every few years onto something interesting and unique." (The futuristic-looking telescope has even served as a backdrop for two Hollywood movies.)
Still, until recently, the telescope labored under two severe limitations. First, because of its spherical shape, the dish didn't fully focus all its energy at a single point the way more traditional parabolic radio dishes do. To compensate, researchers had to build long cumbersome antennas to fully focus the signal.
Unfortunately, each antenna could only collect a very narrow range of frequencies. It was as though researchers were having to decipher a color picture by looking at only one color at a time - and having to build a new pair of glasses for each new color they wanted to see, says Arecibo's Dr. Altschuler.
So in the 1990s, the observatory embarked on a huge, $25 million-plus renovation that replaced the antennas with two huge "corrective lenses." The new mirrors not only use more of the dish's area, they collect a much broader range of radio frequencies. To further increase the telescope's accuracy, workmen adjusted screw by screw the dish's nearly 39,000 aluminum panels to bring them within fractions of an inch of a perfect spherical shape.
Arecibo's second big limitation has been its single-receiver design. While the instrument can look deep into space, it can only "see" one point at a time. So in a second major upgrade, known as the Arecibo L-band Feed Array or ALFA, engineers will replace the current receiver and add a ring of six additional ones. Effectively, the telescope will see seven points in the sky at once. (To increase their sensitivity, the receivers are cooled down to minus 459 degrees F. - nearly absolute 0.)
"With seven times the number of beams, you can go seven times faster," says Joel Weisberg, professor of physics and astronomy at Carleton College in Northfield, Minn. It's ALFA that will allow Arecibo to do the large surveys of sky in reasonable time.
One of the biggest beneficiaries of the upgrades - and one of the few current examples of piggyback research in radio astronomy - is the Search for Extraterrestrial Intelligence. SETI has managed to run continuously for 25 years at Arecibo by letting other scientists determine where the telescope will point. But SETI keeps its listening equipment open, hoping to pick up a signal from an alien civilization.
"You don't know what frequency ET might broadcast on, so you want to look at broad parts of the spectrum," says Dan Werthimer, chief scientist of the SETI@home project, which allows individuals' computers to analyze the data the group receives. Once the upgrades are done, new SETI searches will be "hundreds of times more powerful than what we were doing before. So it means we have a much better chance of bagging an extra-terrestrial."
Besides listening to signals from the cosmos, the telescope also sends out radar beams and listens for their echo from distant objects. With the updates to the instrument, astronomers expect to find out even more about what lies out in space.
"We can point an instrument at a small object in the solar system or the moon of a planet at night, project a small beam on it, and get a reflection" back, says Arecibo's Altschuler, leaning over the railing overlooking the giant dish as the receiver above slides into a new position. "We can take an object that's a mile across and is 10 million miles away and take a snapshot of it. Now that's pretty amazing."