A class of strange radio signals detected at Australia's Parkes Observatory (above) is the work of nearby microwave ovens.
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A class of strange radio signals detected at Australia's Parkes Observatory (above) is the work of nearby microwave ovens.

Rogue Microwave Ovens Are the Culprits Behind Mysterious Radio Signals

Let’s be clear about one thing: Reheating coffee in the microwave is always a poor life choice. But it becomes especially unwise if you’re using a microwave oven near a radio telescope and you’re so eager for that icky, burnt and wholly unsatisfying taste that you prematurely pop the coffee out before the oven’s timer goes off.


You may have just unleashed a small but mighty radio signal that could be detected by a nearby, sensitive radio telescope. If you happen to be reheating your coffee at the Parkes Observatory in Australia, you could be contributing to the growing collection of mysterious radio signals known as perytons. Well, the collection of formerly mysterious radio signals: A study posted to the arXiv on April 9 identified microwave ovens at the Parkes site as the rather mundane source of perytons.

“It was quite surprising that it ended up being microwaves,” says study author Emily Petroff of Australia’s Swinburne University of Technology.

For years, astronomers had been puzzled by these brief but intense bursts of radio waves that in some ways appeared to be coming from deep space. There have been dozens of reported perytons, some dating back to the 1990s, and theories about the signals’ origin included ball lightning, aircraft, and components of the telescopes themselves.

But almost since the beginning, one thing has been clear about perytons: Despite mimicking a deep space signal, they’re produced by something that’s somewhere near Earth. Astronomers knew that perytons were locally grown because the signals simultaneously showed up in multiple viewing fields rather than arriving from a single point, as distant signals do. Just how close to Earth was a mystery until now.

Petroff and her colleagues discovered the source of perytons after they installed a real-time radio interference monitor at the Parkes telescope. In January, the telescope detected three of the signals – and the interference monitor picked up three simultaneous interference signatures. The team recognized the interloping frequencies as possibly belonging to a microwave oven.

When Petroff and her colleagues tested their hypothesis, they found they could create perytons on demand simply by opening the oven door before the timer had dinged.

Why is the impatience over a warming Hot Pocket important? If you open the microwave door before the timer goes off, the thing in the oven that produces microwaves – it’s called a magnetron – hasn’t had a chance to completely shut off. And so, the microwave oven is briefly transmitting radio waves into the open.

“Radio emission escaping from microwave ovens during the magnetron shut-down phase neatly explain all of the observed properties of the peryton signals,” the study authors write. They then identified the offending microwaves as the ones in the staff kitchen and visitors center at the observatory.

Sensitive radio telescopes, like the ones at Parkes, the Arecibo Observatory in Puerto Rico, and the National Radio Astronomy Observatory in Green Bank, West Virginia, can easily detect those rogue microwaves if the telescopes are pointed in the right direction.

“Microwave ovens are a problem for us – and none exist on site. They are prohibited,” says Arecibo director Robert Kerr. Other facilities that don’t ban microwave ovens altogether shield them in enclosures called Faraday cages, which are supposed to prevent detectable radiation from leaking out. In general, scientists try very hard to eliminate any potential source of Earth-based interference from mucking up radio astronomy data – and that means things like cell phones are a no-no near telescopes.

“Alas, radio telescope sites may appear to be occupied by Luddites,” Kerr says. “No microwaves, no cell phones, no wireless routers, no bluetooth printers or headphones, and – more due to funding – often no food.”

The U.S. Town With No Cell Phones or Wi-Fi

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So, one of astrophysics’ more exotic mysteries has a surprisingly down-to-Earth solution. But what does this mean about fast radio bursts, perytons’ enigmatic cousins that truly appear to be coming from very, very far away and have no known origin? (A favorite speculation among readers is “aliens.”) Might they also be coming from Earth?

It seems unlikely, Petroff and her colleagues argue. The intricacies of the fast radio burst signals still suggest an extragalactic origin. And there are revealing differences in the time distributions of the two types of signals. As one might expect from a cosmological signal, fast radio bursts tend to show up rather randomly around the clock. But, perhaps unsurprisingly in retrospect, the peryton data show those signals “clustering near the lunchtime hour.”

Aha! A clue, Sherlock.