Mysterious Deep-Space Radio Signals Trace Back to a Janky Old Microwave

It's not hard to fuck with a radio telescope. As an illustration, consider the Green Bank Telescope in rural West Virginia—and watch Motherboard's Green Bank documentary while you're at it—which, despite being the largest fully steerable radio telescope on Earth, remains highly sensitive to even the slightest background signal. Don't plan on getting near the thing with a cell phone, digital camera, or even a modern electronics-based automobile. Same goes for any other terrestrial radio astronomy equipment: the signals these telescopes hunt for are the barest wisps, at least compared to an iPhone or, as it turns out, a janky old microwave oven.

A microwave. This is the explanation offered by a recent paper posted to arXiv for a series of should-be-impossible signals recorded at the Parkes Radio Telescope in Australia—lingering mysteries that have even led some astronomers to suggest a non-human artificial source.

Around 2001, the Parkes telescope registered a single burst of anomalous radio activity, characterized as a fast radio burst (FRB). This FRB, a highly strange event lasting mere milliseconds and consisting of intense gigahertz wavelengths, was noticed only on later examination of archival telescope data. It was first reported in Science magazine in 2007.

The FRB's higher frequencies arrived first, with the lower frequencies trailing behind, which suggested that the signal had traveled a great distance with an origin far outside of the Milky Way. A hunt ensued, with astronomers across the globe pouring through archival data hoping to find similar events. 40 more were found at the Parkes telescope alone, with astronomers elsewhere revealing similar events. The source(s) remained unknown.

In addition, the Parkes telescope came up with 25 FRB-style events that were different than the others, with the frequency arrival times occurring with no delay between higher and lower bands. "Although they covered a wide frequency range just like the other FRBs, the frequency-time structures of many of these events defied any physical model, and they did not show differences in the arrival times between the higher frequencies and the lower frequencies of the burst," reports Alexander Hellemans at IEEE Spectrum.

What's more, the signals seemed to come from all directions. The Parkes astronomers called their mysterious signals perytons, after the mythological hybrid stag-bird creature described by Jorge Luis Borges in his Book of Imaginary Beings. They were impossible but real—or real enough.

An interesting quirk of the perytons was that they only seemed to arrive on weekdays, which pointed even more so the likelihood that they were manmade (and kept human schedules).

In 2014, the astronomers set up a radio frequency interference monitor at the observatory, which pointed to the possibility of the signals originating in microwave ovens in use around the facility. But when they went to test the theory out and set up a detector next to a potential culprit, no radio pulses were detected. For a moment, the mystery once again deepened.

But only for a moment. "Subsequent tests revealed that a peryton can be generated at 1.4 GHz when a microwave oven door is opened prematurely and the telescope is at an appropriate relative angle," the current paper reports. "Radio emission escaping from microwave ovens during the magnetron shut-down phase neatly explain all of the observed properties of the peryton signals." The perytons were people opening microwave doors before the timer finished.

There's probably a moral in that—some astronomer's Cup Noodles impatience resulting in a decade-long astronomical mystery. Or maybe not.