Fast Radio Bursts - ET or BT?

 More fun than aliens

Want to save a few minutes of your life for something useful? Don't read any article headlined "Is this evidence of alien life?". It, more than any other, will follow the rule that any headline that's a question has the  answer "No!". 

There are always small batches of such headlines floating around, as there are always odd things going on that could conceivably be aliens, if only reality wasn't going to barge in rudely and say "My ball, I think". Most recently, such headlines have clustered around the strange bright spot on Ceres (here Alienated by The Register, which at least has the good grace to answer "No" as the first word in the subhead - having your SEO and mocking it being a hallmark of the doughty Vultures), Another batch was triggered by Putin's temporary disappearance. I won't dignify that with a link, but yes, really.

In general, the more scientific the journal the less likely little green men are to appear in a headline. So, what on earth (or off it) is New Scientist doing with "Is this ET?" - published the day before April 1st, to boot? Is it really ET?

I refer m'learned reader to my first paragraph.

There is some excuse for New Scientist. It's reporting on a fascinating phenomenon called Fast Radio Bursts, which have been puzzling radio astronomers for a while. These are - you've guessed it - transient bursts of radio energy that appear to come from outside the Galaxy but cannot be explained by any known cosmic mechanism. As this is the sort of thing that SETI watchers explicitly listen for and anything that can't immediately be explained could perhaps be the result of Vulcan broadcasters, then the question isn't actually illegal.

But it's still not a good question to ask in a headline if there's a more plausible answer. In this case, a little digging not only provides one but - and here one must frown a little sadly at the grown-ups - also comes up with a reason to have some fun with creatures even more extraordinary than aliens. There really are bizarre beasts at work, and New Scientist passed them over in favour of boring old bug-eyed monsters.

Ladies and gentlemen - no, FRBs are not aliens. Instead, I give you (probably) perytons - mythical beasts that are a cross between a stag and a bird.

The New Scientist article actually gets just about a far as you can in admitting this without being quite able to give up its fond hope for real aliens. The shame is that the piece is based on an Arxiv paper that doesn't pull that punch, leaving the reader in no doubt that perytons are afoot (the researchers, Hippke and Domainko, know how to leave the cake of conclusion on the plate for the reader while simultaneously scoffing it down).

Let's not bury the lede any deeoer. Perytons were created by the sainted Borges, who not-really-claimed to have fished them out of a non-existent medieval bestiary. Since then, they've been adopted by various fans of the fantastic, such as video game writers and Dungeons and Dragonistas. Most recently, this chmeric creation has found a roost in radio astronomy, where it is now shorthand for radio signals that  appear to have non-human causes but are really the byproduct of Homo sapiens' own radio activity.

FRBs look cosmic because they're rare - we've only spotted around a dozen - and have a key characteristic of very distant signals; they look like a very intense pulse of energy that's been smeared by a massive trip through intergalactic space. Pulses of radio energy squirt out lots of radio frequencies all at once, high and low, but the low frequency signals get delayed by free electrons hanging around between the stars. Thus, if a signal comes in from far enough away, by the time it gets to us the high frequencies arrive first and the lower stuff lags behind.

Called dispersion, this smearing mechanism is a good way of estimating distance to far-away radio sources such as pulsars, and it can also be used to map the density of the interstellar medium. (This is truly fascinating and eerily beautiful, and I'll get back to this in the future.)

FRBs do indeed show lots of dispersion. So much so, they have to come from outside the Galaxy. But if they're that distant, they must also be unbelievably powerful, far more so than pulsars - which, being staggeringly puissant spinning neutron stars, are already in the top league of ferociously energetic cosmic beasts. It beggars belief that such things could be natural.

So, ET? No! I've told you already! Perytons! There are three main reasons for believing this: iirst, of the eleven FRBs detected to date, ten have been from one site (the Parkes radio telescope). Second, while the dispersion measures are extreme, they're all very closely mathematically related - they have gaps between them that are integer multiples of exactly half the FRB smallest dispersion measure detected. Remember that the dispersion measure is a proxy for the distance of the event from the Earth - for this to be true in this case, the sources of the FRBs must be precisely arranged in space at exact distances from us.

And, finally, the FRBs have arrived in the telescopes apparently well-synchronised to Earthly seconds, the universal timing system that we use to make  our computers, satellites and mobile phone transmitters march in step.

If this is ET, the only reason it'll have pointed ears is because it's a troll.

The trouble with using dispersion to conclude distance is that it assumes the nature of the original pulse. With pulsars - also semi-facetiously labelled Little Green Men when first discovered by Joceyln Bell - we have enormous numbers of observations and a good model of what's going on. FRBs have none of this - if the original transmission just happens to sweep out high frequencies first and low frequencies later, then it'll look far away but could be on our own sofa. Called chirping, this is a very common technique in radar and other related areas. (Very common; i'm listening to a Chinese transmitter doing it on 14 MHz right now.)

A despressingly large amount of time and effort goes into identifying and squashing perytons. Entire frequency bands are marked off-limits. Governments create huge quiet-sky reserves in remote countryside for radio astronomers, where all transmitters are verboten. But still, hundreds and thousands of satellites are up there, full of radio systems and digital computers, all of which radiate some interference as they drift past the sensitive dishes of the deep-space listeners, and all manner of passive but reflective clutter in the sky can bounce back terrestrial interference over thousands of miles.

The herds of perytons sweep majestically across the sky, jabbering like antlered jackdaws: to date, not one has proved to be anything from a race more exotic than our own.

Which is slightly sad, but still a good story in its own right. More so,, I think, than could-it-be-aliens-no-not-really.

(Peryton image: "Perytonmontage" by (Copulating)_Red-shouldered_Hawks.jpg: leppyoneRedDeerCaithness.jpg:derivative work: Tsaag Valren. Licensed under CC BY-SA 3.0 via Wikimedia Commons - https://commons.wikimedia.org/wiki/File:Perytonmontage.jpg#/media/File:Perytonmontage.jpg)