Among Australians, the Parkes radio telescope is known as the “grand old lady of astronomy.” In terms of discoveries, it’s the most successful astronomical instrument in the country, and researchers there have spent more than four decades scanning the skies for distant objects, interstellar magnetic fields, ancient radio signals, even signs of extraterrestrial life.

About 17 years ago, the Parkes started getting pinged with an especially inexplicable type of signal. The mysterious bursts bore some of the hallmarks of a long travel through space but appeared to be coming from our own planet. Sarah Burke-Spolaor, an astrophysicist at the telescope who first studied the strange signals, dubbed them “perytons” after a mythological part-bird, part-stag creature in a Jorge Luis Borges story. It was a fitting namesake for signals, she explained to the Atlantic — both are half Earth-bound, half not.

Burke-Spolaor offered a few possible explanations for the perytons — perhaps it was lightning or cosmic rays or high-atmosphere electronic discharges called “sprites.” But those theories were mostly speculative.

That was in 2010. Five years later, astronomers still had no clue what was causing the brief blips in their data, and it bothered them. The presence of perytons called into question other research they’d been doing on an elusive phenomenon called a Fast Radio Burst (FRB), a short, intense signal that seemed to come from something swift and cataclysmic in distant space. The perytons weren’t so different from these FRBs — if they came from Earth, perhaps the FRBs did, too.

PhD student Emily Petroff decided to clear things up once and for all. She began searching for the perytons in earnest, and after six months of study, she found their source.

It wasn’t lightning or sprites or messages from an alien civilization. It was the microwave in the lab kitchen. It spit out a short radio signal when Petroff’s co-workers opened the door before the cooking cycle was over.

Did she feel silly that the mysterious signals came from someplace so mundane?

“In a way, yes, because to figure out that I’d been spending the last six months looking for microwaves felt kind of disappointing,” she told The Washington Post. “But it was also good, because it was something we can control and test.”

Petroff’s research didn’t lead her into the kitchen right way. First, she spent several months poring over data from the telescope, looking for signs of recent perytons. Her best lead came in January, when she detected three perytons in the same week.

“So we started hunting around on site to see if anything special was happening that week,” Petroff said. “And the staff said ‘No, nothing special, but just so you know we’ve installed a new interference monitor. .. Why don’t you look at the data?'”

Petroff did and found that the signals were occurring at a frequency of about 2.4 GHz — the same frequency at which microwaves and other appliances operate. So she began testing the center’s microwaves for interference. But they still weren’t finding signals that matched the perytons.

The real breakthrough came when she and her colleagues realized that the microwaves emitted a brief, lower frequency burst before powering down if someone opened the door before the timer was up. This high-then-low frequency phenomenon mimics the characteristics of the FRBs, though it’s caused by something much more down to Earth: a hungry astronomer impatient for lunch.

Petroff’s study of the perytons and their source, which was published last month in the Monthly Notices of the Royal Astronomical Society, includes another tip-off that the signals weren’t as mysterious as they seemed: The number of perytons detected by the telescope surges around noon, right when staff are breaking for lunch.

And although Petroff may be disappointed to have spent six months chasing after signals from the kitchen rather than outer space, she’s glad she did so.

“We don’t have to worry about them anymore,” she said. “Now that we know what’s causing perytons, we’re even more confident that FRBs are coming from real astrophysical sources. We can get back to the bigger mystery.”

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