By Jonny Lupsha, Wondrium Staff Writer
The iconic Arecibo Observatory telescope in Puerto Rico collapsed, Business Insider reported. Its suspended platform, which weighed 900 tons, fell into the dish portion of the telescope December 1. Radio telescopes capture radio waves for study.
According to Business Insider, one of the most iconic and recognizable radio telescopes in the world—in fact, the second-largest on Earth—has been destroyed. “The Arecibo Observatory’s 1,000-foot-diameter telescope collapsed at about 7:55 a.m. Tuesday [December 1] in Puerto Rico,” the article said. “The telescope’s 900-ton platform, which was suspended 450 feet in the air to send and receive radio waves, crashed into its disk below, pulling down with it the tops of three support towers.
“The collapse was not unexpected: Following two cable breaks in August and November, experts determined that the radio telescope was so structurally unsound that it had to be decommissioned.”
While optical telescopes like those on Mauna Kea in Hawaii reach a maximum length of about 10 meters across, radio telescopes can be 50 times that size. Here’s what they do.
So what exactly do radio telescopes do?
“A radio telescope is a thing that collects radio waves from a certain direction in the sky and focuses it onto a point where a receiver can pick up the signal,” said Dr. Felix J. Lockman, Green Bank Telescope Principal Scientist at the Green Bank Observatory. “The receiver does a number of things, including amplify the signal. The signal is then passed along to systems that detect and measure it.”
A radio telescope features a wire called a probe that carries electricity. The probe, usually made of a metal-like copper or aluminum, gets its name because it probes the electric field for radio waves. Dr. Lockman said that electric current is just an organized motion of the electrons swimming around on the surfaces of metal, such as probes. When those electrons are put in motion by being pushed by an electromagnetic wave, the wire becomes an antenna.
“An antenna is a device that intercepts an electromagnetic wave in free space and turns it into an electric current in a wire,” he said. “The antenna for the radio in your car does the same thing: It catches incoming radio waves and turns them into a current in a wire.”
Finally, the purpose of a radio telescope dish is to capture as much radio energy as possible and focus it onto the probe.
Is There Anybody Out There?
Incoming radio waves reach the dish and, due to the dish’s shape, are bounced back up at an inward angle to a point above the dish’s center. This point is called the primary focal point or the prime focus. Radio telescopes either have a receiver at the prime focus or another reflective surface—called a subreflector—that bounces the radio signals back down toward the center of the dish itself where a feed horn sits and carries the signal to the receiver.
“The first thing we do is amplify it,” Dr. Lockman said. “We feed the signal into a device that makes it stronger by many times, [maybe] a thousand times, so that it turns from a celestial whisper into something that we can measure.”
The next step is for radio astronomers to change the frequency of the signal while preserving all the information that the signal contains. This, Dr. Lockman said, is a process called heterodyning, or mixing, which is done in case the listener wants to measure a celestial signal over very fine frequency intervals.
“If you own a radio, you will see that it covers a number of bands: AM, FM, maybe others,” he said. “That means that the radio signals are coming through the air at frequencies like, say, 106.3 megahertz—that’s in the FM band—or 1370 kilohertz in the AM band. Our radio uses heterodyning to mix those signals down into the audio range—kilohertz—where our ears work.
“The speakers in our radios don’t know the frequency of the radio station, because by the time the radio signal gets to the speakers, it’s been mixed down to audio.”
The search for celestial radio signals will have to continue on without Arecibo Observatory.
Dr. Felix J. Lockman contributed to this article. Dr. Lockman is the Green Bank Telescope Principal Scientist at the Green Bank Observatory, a facility of the National Science Foundation. He did his undergraduate work at Drexel University and received his PhD from the University of Massachusetts Amherst.