Astronomy mourns the loss of Arecibo by Wladimir Lyra

(Originally published in the Las Cruces Sun News on December 6, 2020 – link)

On Tuesday Dec 1st 2020, the astronomy world woke up to the news that one of its major facilities, the radiotelescope of Arecibo Observatory, had collapsed.

Unlike conventional telescopes like Hubble, that collects the same type of light our eyes see and therefore use mirrors to focus that light, a radiotelescope sees in radio waves. Although we tend to think of radio as something we listen to, there is no fundamental distinction between radio waves and visible light. Both are electromagnetic waves, oscillating in a repeating pattern of fixed length. The difference is that this length for visible light is shorter than a millionth of an inch, while for radio waves it is longer than several yards. Radio waves are traveling around you at this very moment. When you switch on “the radio” in your car, the radio waves captured by the antenna are converted into sound waves. A radiotelescope operates in about the same way, except for the conversion to sound. There is an antenna, that captures the radio waves, focusing it into a receiver. The difference between your radio tuning in to your favorite song and a radiotelescope unraveling the mysteries of the Universe is just the size of the antenna.

Covering an area of twenty acres amid the lush tropical forests of Puerto Rico, Arecibo’s giant antenna measured over 1000 feet in diameter. Over 150 feet deep, the hemispherical dish focused the radio waves into a receiver suspended 400 feet above it. The telescope was rendered inoperative in August, when a cable crashed onto the antenna. A second cable crashed in November, jeopardizing the platform that kept the receiver suspended. The receiver, weighting 2 million pounds, having lost the support of two of the suspension cables, finally fell and crashed onto the dish.

Built in the 1960s, Arecibo produced major astronomical discoveries. It was responsible for Nobel prize-winning research, the discovery of a pair of pulsars orbiting each other. The name pulsar refers to what at first was a perplexing phenomenon: cosmic pulses of radio waves, repeating very regularly, every 1.33 seconds. The enigmatic pulses were even thought to be a radio message from an alien civilization, and dubbed “little green men”. It wasn’t until a second pulsar was discovered that it became clear they were a natural phenomenon, found out to be a bizarre type of astronomical body, called neutron stars. Neutron stars are very dense objects, weighting as much as the Sun, but compressed to a few miles in diameter. The gravity is so intense that the electrons, usually orbiting the nucleus of the atom, are pressed onto the nucleus, combining with the protons and converting all matter into neutrons. The magnetic field of the neutron star produce auroras, like on Earth, except that in this case the auroras are so intense we can see them from light years away. We see them as pulses because the rotation of the neutron star brings the aurora in and out of our line of sight, like a lighthouse. Arecibo’s detection of a pair of pulsars, so massive and so close to each other, allowed for a decisive test of our best theory of gravity, Einstein’s general relativity. Unsurprisingly, Einstein was right.

Another property made Arecibo special: not only it received radio waves, Arecibo also emitted them. It sent radio waves to bounce off nearby objects, working as a planetary radar. Indeed, Arecibo played a vital role on protecting the Earth from deadly asteroid impacts. Its radar would echo off nearby dangerous asteroids, telling us their position to within a few feet. This very accurate tracking allowed us to predict if the asteroid was at risk of impacting Earth. Among the many scientific setbacks the demise of Arecibo represents, the loss of the planetary radar is perhaps the most significant one.

For astronomy, the loss of Arecibo is like a death in the family. But its collapse also reveals a symptom of something deeper happening in US science. In 2016, Arecibo had been surpassed as world’s largest radiotelescope by the Chinese Five Hundred Meter Aperture Spherical Telescope (FAST). The loss of Arecibo now elevates FAST to an even more unique status. A parallel can also be drawn with the 1993 cancellation of the Superconducting Super Collider in Texas, after 2 billion dollars had already been spent on it. As a result, particle physics was advanced not in the US but in Europe, culminating with the 2012 discovery of the Higgs boson at the Large Hadron Supercollider in Switzerland. The disaster at Arecibo should be taken as the painful but obvious lesson that if we do not actively maintain our position of leadership in basic science, we will eventually lose it.


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