The source of puzzling radio wave bursts detected by two of the world's largest telescopes has been found, and the answer turns out to come from the research facilities' tea rooms, not extragalactic space.
Earlier this year, Swinburne University's Emily Petroff was the lead author of a report on the first observation of a fast radio burst (FRB) in real time. Previously, the enormously powerful but poorly understood events known as FRBs had only been detected in the records of large radio telescopes years after they happened.
However, among those records was something else, which astronomers named perytons. The first peryton detected was in 1998, although it was not recognized as such until 2011. Perytons look sufficiently like FRBs that astronomers even speculated that the first FRB, known as 010724, might actually have been a peryton.
Perytons last about half a second and are “frequency-swept,” meaning different frequencies arrive at different times, which in perytons's case means the high frequencies appear first. Petroff says, frequency-sweeping is commonly associated with signals that have passed through an interstellar medium that has delayed certain frequencies more than others.
However, while FRBs are believed to come from outside our own galaxy, perytons were thought to be terrestrial in origin, since they registered on multiple beams of the radio telescopes, something that should only be possible for events that are very nearby or spread across a huge area of the sky.
However, according to Petroff, “A lot of theories thought it might be atmospheric; radio pulses from lighting or ball lightning, etc.” So Petroff set out to solve the problem. As one of her co-authors, Dr. Evan Keane, said on twitter, “As a scientist you are basically a detective solving mysteries—it's fun.”
One clue Petroff had was that all recorded perytons were observed during daylight, and indeed during business hours. When the observatory at Parkes installed a radio frequency interference (RFI) monitor, it picked up signals coinciding with some perytons detected by the famous dish. This confirmed the local nature of the events and indicated the signal was also occurring at frequencies beyond what the radio telescope can detect.
Using this information, Petroff narrowed down the possibilities until she eventually identified the source—microwave ovens in the observatory tea room opened while in operation. A test conducted on March 17 confirmed two ovens could reproduce perytons whenever the telescope was pointed appropriately. Although modern ovens have automatic mechanisms to switch-off when opened prematurely, it seems they don't do this without complaint. “We're still not sure how they are causing this signal,” Petroff says, “It might have something to do with discharge of energy in the oven's magnetron when shutting down.”
The demonstration that ovens are the cause of petryons, and that FRB 010724 is almost certainly a real FRB, has been accepted for the Monthly Notices of the Royal Astronomical Society. It is also available on arXiv.org, with Petroff once again the first author, despite having yet to complete her PhD.
Petroff told IFLS that “It takes a 64m dish to pick up the radiation,” so she doubts perytons are dangerous to those too impatient to stop the oven before opening. Nevertheless, she has advised on Twitter that it “Still might be good to advise staff to wait. It's a small lesson in patience.”
Petroff says the culprit has not been identified and denies plans to “point fingers.”
Credit: Katie Mack. @AstroKatie's handy guide to distinguishing perytons from fast radio bursts.