The Perytons of Parkes

Summary

From 1998 the Parkes radio telescope recorded millisecond bursts that mimicked signals from deep space. In 2015 they were traced to its microwave ovens.

The bursts, called perytons, swept down in frequency the way a pulse does after crossing interstellar space, and they resembled the first fast radio burst closely enough to throw doubt on it. The source turned out to be an oven door opened before the timer ran out, and the finding cleared the fast radio bursts rather than condemning them.

What is documented

The telescope. The Parkes radio telescope, run by CSIRO, is a 64-metre dish in New South Wales. Its multibeam receiver observes the sky in 13 beams at once, at frequencies around 1.4 gigahertz.

The first fast radio burst. In 2007 Duncan Lorimer and colleagues reported a single, very bright pulse lasting less than 5 milliseconds, found in Parkes data recorded on 24 July 2001. Its frequencies arrived in a sweep, the higher first, matching the delay that ionised gas imposes on a signal crossing great distances. Its dispersion measure, the quantity that records that delay, was 375 (in units of parsecs per cubic centimetre). They proposed an origin outside our galaxy. It is now known as FRB 010724, or the Lorimer burst (AR-0028).

Perytons. In 2011 Burke-Spolaor and colleagues reported 16 pulses in archival Parkes data from 1998 to 2003, most with a frequency sweep "resembling the Lorimer Burst". Unlike a distant source, which is seen in one beam or a few, these appeared in all 13 beams, at strengths within a factor of four of each other, entering through the telescope's sidelobes. They were "of clearly terrestrial origin", with properties unlike any known terrestrial source of broad-band radio emission. The authors named them perytons, after the winged elk of mythology that casts the shadow of a man, choosing a name "unassociated with an exact physical phenomenon". They wrote that the new detections "cast doubt on the extragalactic interpretation" of the Lorimer burst.

The pattern. By 2015, 46 perytons had been detected at Parkes. The 25 described in the literature had all occurred during office hours, predominantly on weekdays, and they clustered around the lunch hour. Similar signals were reported at the Bleien Radio Observatory. Their dispersion measures fell in two groups, around 200 and around 400.

The monitor. In December 2014 a monitor for radio interference, covering 402 megahertz to 3 gigahertz, was installed on the Parkes site. Three perytons followed, on 19, 22 and 23 January 2015. For each, the monitor recorded emission between 2.3 and 2.5 gigahertz at the same moment. Microwave ovens heat food at about 2.4 gigahertz.

The ovens. Three microwave ovens near the telescope were in frequent use: one in the tower below the dish, one in the visitors centre, and one in the staff kitchen in a building known as the Woolshed, about 100 metres from the dish. Petroff and colleagues tested them on 27 February, 12 March and 17 March 2015. On 17 March, instead of letting the staff kitchen oven finish its cycle, they stopped it by opening the door. The telescope recorded three bright perytons, each at the moment the door was opened, with dispersion measures of 410.3, 410.3 and 399.6.

The mechanism. The emission escapes when the oven's magnetron is shutting down and the door is already open. It reaches the telescope's 1.4-gigahertz receiver as a sweep in frequency that imitates the dispersion of a distant pulse, and it is recorded only when the dish is pointed at a suitable angle to the oven.

The burst was not an oven. Petroff's team examined FRB 010724 against the new explanation. It was bright in three beams, as a source in the telescope's main beam would be. At the position the dish was pointing, its own surface blocked the line of sight from the Woolshed oven to the receiver cabin. And it arrived at 19:50 UT, 5:50 am Australian Eastern Standard Time, when the visitors centre was closed and unstaffed. They concluded that "perytons and FRBs arise from disparate origins".

Leading explanations

Microwave ovens opened before the end of their cycle. Established. The coincidence with 2.3 to 2.5 gigahertz emission in January 2015, the office-hours timing, and the production of perytons on demand on 17 March 2015 together identify the source. The paper was published in Monthly Notices of the Royal Astronomical Society in 2015.

A natural terrestrial source. Rejected. Before 2015 the perytons were accepted as earthly but unexplained; one possibility, as Science News summarised it, was "some meteorological phenomenon". The ovens, in the words of Petroff's team, "neatly explain all of the observed properties of the peryton signals".

A common source for perytons and fast radio bursts. Rejected. The one burst the perytons most resembled could not have come from the ovens. Fast radio bursts have since been detected by other telescopes, and in 2017 one source was localised to its host galaxy (AR-0028).

Current status

Later explained. Perytons are microwave-oven emissions, recorded when an oven door near the telescope is opened before the cycle ends. The cause was identified with an interference monitor and confirmed by making perytons on demand.

The registry keeps the record because the perytons were a real anomaly for 17 years, and because their explanation mattered beyond Parkes. Their resemblance to the first fast radio burst had cast doubt on the whole class. Once the ovens were found, the doubt was lifted.

Last reviewed: September 2026. Records are provisional. Where the evidence changes, the entry changes. Found an error? Tell us.