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Rascally ravens are rapping ice off some frozen pipes at the Hanford LIGO detection site to create their own snow cones on hot days -- and they're creating a world of trouble for astrophysicists
The Advanced Laser Interferometer Gravitational-Wave Observatory (aLIGO) is a pair of vibration detectors, one is located in the desert in Washington state whilst its twin is located in Louisiana. aLIGO was designed to directly observe and measure gravitational waves created by cosmic cataclysms that vibrate through the universe like ripples across a pond’s surface, as predicted by Albert Einstein 100 years ago. Data collected by the aLIGO observatories, which were designed to test Einstein’s general theory of relativity, resulted in the 2017 Nobel Prize in Physics.
Basically, aLIGO functions like a giant, ultra-sensitive, ear attuned to the distant murmurs of the cosmos. The aLIGO can register vibrations from a truck trundling down a nearby road winding through the desert, a small airplane whirring overhead, and it can even detect the vibrations from a refrigerator humming in a nearby building. So sensitive is the aLIGO that it can measure a change in length that is “equivalent to the width of an atom in the distance from the Earth to the Sun.”
Of course, this extreme sensitivity makes it incredibly easy for small earthly sounds to cause big problems.
To fine-tune the sensitivity of aLIGO to vibrations created by astrophysical events, sources of both instrumental and environmental racket must be identified and reduced or blocked. Fine-tuning this expensive precision instrument is a never-ending task that even employs its own squadron of physicists. So when physicist Beverly Berger, ombudsperson of the LIGO Scientific Collaboration, spotted a new series of unidentified background noises that mysteriously popped up in July 2017, she and her collaborators were understandably very curious and determined to get to the bottom of it, and quickly.
According to Dr. Berger, who spoke at a recent meeting of the American Physical Society on 16 April (ref), the weird signal showed up in the data as a series of short-duration staccato bursts, otherwise known as “glitches”. Upon closer examination, these glitches certainly didn’t look like gravitational waves. They also didn’t look like air pressure disturbances from airplane propellers -- common in the area -- and they didn’t resemble any of the other sounds that the researchers were familiar with. Nor were any similar glitches detected by LIGO’s twin instrument in Louisiana, so the source of the racket could only be at Hanford. So what was creating these noises? And more important, if the glitches were not created by an astrophysical event, could they be prevented somehow?
“Sometimes, even if the cause is known, the problem cannot be easily fixed. However, the now understood character of the noise can be used to avoid confusing it with an astrophysical signal,” Dr. Berger said in her presentation.
The first clue was provided by microphones placed around the Hanford facility by physicist Robert Schofield, a Research Assistant Professor at the University of Oregon, and his noise reduction team as part of their endless battle to detect and eliminate extraneous environmental disturbances. It was one of these microphones that detected the staccato noise. And one of the recordings sounded vaguely familiar ...
When the scientists checked the source of the sound, they discovered telltale marks in ice that had formed on a frozen section of piping near the end of one of the Hanford aLIGO’s 4 kilometer (2.4 mile) arms. Ravens could often been seen perched on these pipes on hot summer days and, in fact, the marks looked suspiciously like peckmarks made by a large bird beak, suggesting that the local desert-dwelling ravens might be chipping the ice to quench their thirst. But were thirsty ravens the source of this staccato sound? One of the scientists, graduate student Pep Covas, conducted a small experiment where he rapped on the pipe to see if the resulting vibrations resembled the suspected raven-created glitches.
They did.
Conveniently, a raven showed up to observe the proceedings. The bird then demonstrated her technique for creating a snow cone by chipping ice from the pipe whilst the scientists watched.
Sadly for the thirsty ravens, the researchers had seen enough. They concluded that the ravens were to blame for their perplexing data glitches. They quickly insulated the pipes so water could no longer precipitate and freeze on them, thereby removing any pipe-tapping temptations for the rascally ravens.
Bird fans may recall that this isn’t the first time that birds have created problems for astronomers and physicists. For example, in May 2009, the accident-plagued Large Hadron Collider’s superconducting magnets, located above the particle accelerator ring, suffered severe overheating. Scientists there believe that a bird flying over the equipment dropped a baguette into it and that was the cause of the problem.
Another example occurred even earlier, in the 1960s, when radio astronomers Robert W. Wilson and Arno A. Penzias were testing the Bell Telephone Laboratories’ radio telescope antenna in Holmdel, New Jersey. This was probably the best -- most sensitive -- radio telescope in the world at the time. Wilson and Penzias were using it to scan for a halo around the Milky Way, but were concerned because their data showed the heavens were far noisier than they expected. They then discovered that a pair of pigeons had set up housekeeping in their radio-antenna and, like all warm-blooded creatures, the birds’ body heat was the source of the radio waves that the telescope picked up.
After Wilson and Penzias removed the pigeons and cleaned their pooh off the antenna, they recognized that the persistent hiss they’d been confounded by was something far more interesting than a halo around the Milky Way: it was the faint buzzing afterglow of the Big Bang, a discovery that earned them the 1978 Nobel Prize in Physics.
Source:
Beverly K. Berger (2018). Abstract: Tracking down the origins of Advanced LIGO noise: some examples, (PDF) APR18 Meeting of The American Physical Society.
Thirsty Ravens’ Tap-Tap-Tapping Creates Data Glitch At LIGO | @GrrlScientist
