The Cosmic Microwave Oven Background

Title: Identifying the source of perytons at the Parkes radio telescope
Authors: E. Petroff, E. F. Keane, E. D. Barr, J. E. Reynolds, J. Sarkissian, P. G. Edwards, J. Stevens, C. Brem, A. Jameson, S. Burke-Spolaor, S. Johnston, N. D. R. Bhat, P. Chandra, S. Kudale, S. Bhandari
First Author’s institution:  Centre for Astrophysics and Supercomputing, Swinburne University of Technology, Australia

Over the past couple of decades the Parkes Radio Telescope in Australia has been picking up two types of mysterious signals, each lasting just a few milliseconds. One kind, the Fast Radio Bursts (FRBs), have come from seemingly random points in the sky at unpredictable times, and are thought to have a (thus far unknown)  astronomical origin. The other kind of signal, perytons, which were named after the mythical winged creatures that cast the shadow of a human, have been found by this paper to have an origin much close to home.

Although the 25 detected perytons are somewhat similar to FRBs, with a comparable spread in frequencies and duration, the author’s suspicions were raised when they noticed that the perytons all happened during office hours, and mostly on weekdays.  When  they corrected for daylight savings, they found that perytons were even more tightly distributed— they mostly came at lunch time. Mostly.

peryton times

Arrival times of perytons (pink) compared with FRBs (blue) at the Parkes Radio Telescope. Real astronomical signals probably don’t all come at lunchtime.

To search for the true origin of the perytons, Petroff et al. took advantage of the fact that the Parkes has just been fitted with a Radio Frequency Interference (RFI) monitor, which continuously scanned the whole sky to detect any background radio sources that might interfere with the astronomical observations.

In the week beginning 19th January 2015 the Parkes radio telescope detected three new perytons. Searching through the RFI data, the authors found that each peryton, with a radio frequency of 1.4GHz, was accompanied by another signal at 2.4GHz. Crucially, they could then compare their results with those from an identical RFI monitor at the nearby ATCA observatory. The 2.4GHz signal was nowhere to be seen in the ATCA data. Not only were the perytons not from space, they had to be coming from somewhere nearby the telescope.

Another clue came when the authors found that, although they had only observed three perytons, there were plenty of 2.4GHz signals in the RFI data that didn’t have an associated peryton. Petroff et al. decided to search for anything that would normally give off 2.4GHz signals, but occasionally emit a 1.4 GHz burst. Suspicion fell on the on-site microwave ovens—not only do they operate at 2.4GHz, the telescope had been pointing in the direction of at least one microwave every time a peryton had been seen.

800px-Microwave_oven

A suspicious-looking microwave. Image Source: Wikimedia Commons

With the suspects cornered, the authors set about trying to create their own perytons. They found that the magnetrons in microwaves naturally emit a 1.4GHz pulse when powering down. Normally this signal is absorbed by the walls of the microwave, but if someone were to open the microwave door before it finished its cycle then the 1.4GHz pulse could escape. Using this technique, the authors were able to generate perytons with a 50 percent success rate. After decades of searching, the source of these mysterious signals had been found.

What about the FRBs? With the perytons confirmed as coming from Earth and not space, doubt was cast on the origin of the FRBs. The authors suggest that the FRBs are astronomical sources, and not linked with the perytons,  for two reasons:

  • The FRBS come at random times and random locations, whereas the perytons were all detected during the day in the general direction of microwaves.
  • The signal from FRBs is consistent with them having traveled through space, with indicators of interaction with interstellar plasma not seen in the perytons.

The authors finish by suggesting a  final test can be made the next time an FRB is observed. If no simultaneous 2.4GHz signal is seen, then it would  conclusively disprove any link between the FRBs and the perytons. What the FRBs really are remains unknown.

 

About David Wilson

PhD student at the University of Warwick working with Professor Boris Gaensicke. I study the remnants of planetary systems at white dwarfs, looking at what they reveal about planet compositions and searching for variability. When not doing that I mostly spend my time reading, writing, playing board games and building various little plastic people.

14 Comments

  1. Interesting post! How do scientists know that FRBs have traveled through space? What kinds of signals or markers does that have?

    Reply
    • The reason we think the FRBs are from outside our galaxy is that the different radio frequencies in the signal arrive at different times- shorter wavelengths first, then longer, all within about 100ms. This is a result of the signal interacting with electrons in between us and the source. As we know how the signal is spread in time, we can work out roughly how many electrons it has interacted with. We have a rough idea of the electron density in the galaxy, and it turns out there aren’t enough electrons between us and any point in our galaxy for the FRBs to have come through- so they must have come from further away. Hope that explains it!

      Reply
  2. You state that FRBs “have come from seemingly random points in the sky at unpredictable times, and are thought to have a (thus far unknown) astronomical origin”, which makes me wonder why scientists are so curious about them. As far as I understand, astronomers don’t pay particular heed to cosmic rays except to remove them from their data as much as possible. Is there a reason why we are so much more interested in FRBs than cosmic rays?

    Reply
  3. I remember seeing this on the news. Proves to show how our instruments work on such a sensitive regime that we don’t think twice about common items interfering.

    Reply
  4. This is truly an epic conclusion to an interesting observation! Has such disruption in data been found at other observatories due to human activities like heating up lunch in a microwave as described here?

    Reply
  5. Crazy! Have these 2.4 GHz pulses been picked up accidentally as part of other data sets? Since we didn’t know their signals could be detected like this, maybe they have found their way into other observational datasets. Should observatories ban microwaves?

    Reply
  6. Hi David, hasn’t there been some speculation that FRBs are from nearby sources instead of having an intergalactic origin? Does this work say anything about this idea?

    Reply
    • See my answer to the first commenter

      Reply
  7. What are some signs that FRBs have traveled through space, i.e. what are the “indicators of interaction with interstellar plasma” you write of?

    Reply
    • See my answer to the first commenter

      Reply
  8. This reminds me of a similar seemingly groundbreaking discovery that was ultimately revealed to be only due to close interaction between the sensitive machinery and human appliances that our TF, Ben Montet shared with us. In the 60s, scientists were at a loss to explain peculiar flares in their images of the night sky, and could not have the same flares replicated by other telescopes running the same observations. It turned out that far from being evidence of some unusual celestial occurrence, the flares were the result of the momentary brightness which flooded the dark room when the astronomers would strike a match to light their cigarettes, to pass the long exposure times. The 60s….

    Reply
  9. Very interesting. Does this work both way? If a simultaneous 2.4GHz signal is seen, does it prove the connection between FRBs and perytons?

    Reply
  10. The authors reckon this could happen once by chance. If it happened twice, then yes we would have to rethink the connection between FRBs and perytons.

    Reply

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