Emily Petroff, at the Parkes radio telescope, has identified the source of mysterious radio bursts – the early opening of microwave ovens. Photo: Supplied

An Australian-based PhD student has cracked an international mystery that had some of the best minds in astrophysics stumped. Working at the Parkes radio telescope in NSW, Emily Petroff has identified the source of mysterious radio bursts of terrestrial origin that mimic signals from outside our own galaxy.

The strange radio signals being detected on Earth, known as "perytons", are very similar in frequency and duration to deep space signals that some astronomers thought could be caused by neutron stars becoming black holes. However, Ms Petroff and her colleagues identified a far more mundane source for perytons – microwave ovens used by astronomers to heat up their pot noodles.

Ms Petroff, a doctoral student at Swinburne University of Technology, identified the source of three perytons detected at Parkes radio telescope in January. This type of radio signal, 25 of which have been observed, are emitted on Earth but closely mimic "fast radio bursts" (FRBs), whose origins are most likely outside our own Milky Way galaxy.

Lunchtime rush: Radio emissions detected at Parkes observatory spike between noon and 3pm.

What had stumped astrophysicists was the similarity between perytons and fast radio bursts. It was clear that FRBs were extragalactic in origin. Writing in an astronomy blog last year, Brian Koberlein, an astrophysicist from the Rochester Institute of Technology, said of FRBs: "These are short, intense pulses of radio energy that have all the hallmarks of being astronomical in origin. One possible source of FRBs could be a neutron star collapsing to a black hole."


So how could it be that similar radio bursts were being detected on Earth?

Ms Petroff told Fairfax Media that further confusion was caused by the fact that perytons and FRBs exhibit similar dispersion in their electromagnetic spectra.

Emily Petroff on the dish of the telescope. Photo: Supplied

The solution to the mystery, published in April in arXiv by Cornell University, comes down to the fact that the brief peryton events at 1.4GHz are associated with shorter wavelength radio signals at a frequency of about 2.3 to 2.5 GHz, the same operating frequency as most microwave ovens. The confusion arose because extragalactic fast radio bursts are also detected at 1.4GHz. Both events also last a similar time period; about 250 milliseconds.

Ms Petroff's paper says: "This suggests that the perytons may be associated with equipment operating at 2.3 to 2.5 GHz, but that some intermittent event or malfunctioning ... is resulting in sporadic emission at 1.4GHz."

It turns out that event was caused by impatient astronomers and other staff opening microwave oven doors before the timer ended. While the ovens operate at the higher frequency during normal operation, opening the doors early causes the oven's magnetrons to issue a very brief burst at the lower 1.4GHz frequency as they power down.

Illustration: Rocco FazzarI

The researchers concluded: "Radio emission escaping from microwave ovens during the magnetron shut-down phase neatly explain all of the observed properties of the peryton signals." Case closed.

Ms Petroff's research has established that the "fast radio bursts" are "excellent candidates" for being extragalactic in origin and require further investigation. Her research has also established that you shouldn't open your microwave oven while searching the furthest depths of the cosmos.