Skeptophilia (skep-to-fil-i-a) (n.) - the love of logical thought, skepticism, and thinking critically. Being an exploration of the applications of skeptical thinking to the world at large, with periodic excursions into linguistics, music, politics, cryptozoology, and why people keep seeing the face of Jesus on grilled cheese sandwiches.

Saturday, July 22, 2023

The celestial lighthouse

Last week I did a piece on three weird astrophysical phenomena -- odd radio circles, high-energy neutrino bursts, and fast blue optical transients -- all of which have thus far defied explanation.  And this week, a paper came out in Nature about a recent discovery adding one more to the list of unexplained celestial curiosities -- one which has the alien intelligence aficionados raising their Spock-like eyebrows in a meaningful manner (although I hasten to point out that there is no evidence that either this one, or the other three I mentioned, have anything to do with you-know-who).

However, the most recent discovery is downright bizarre.  To understand why, a bit of background.

There are many more-or-less understood phenomena in astrophysics that result in a sudden surge in electromagnetic output from an astronomical body.  Some are aperiodic, or at least infrequent, such as fast radio bursts, which were discovered back in 2007 by astrophysicists Duncan Lorimer and David Narkevic.  These are quick, transient pulses in the radio region of the spectrum, and are now thought to be due either to neutron star mergers or starquakes on the surface of magnetars.

Then there are the repeating ones, such as the fast blinking on-and-off of pulsars.  These are the rapidly whirling cores of collapsed massive stars, which funnel out beams of high-energy radiation aligned with the poles of their magnetic fields; because of the star's rotation, the beam appears to pulse, in some cases dozens of times a second.  They were discovered back in 1967 by the brilliant astronomer Jocelyn Bell Burnell, but because no one could figure out what might create a repeating signal that regular, and also because Burnell was a woman in a field almost entirely dominated by men, her discovery was derisively referred to as LGM ("Little Green Men"), and assumed to be from some sort of prosaic terrestrial source.  It was only when more of them were found that astronomers began to take her seriously.  In 1974, the Nobel Prize in Physics was awarded for the development of radio astronomy, and in particular, for the discovery of pulsars...

... to Antony Hewish and Martin Ryle.  Note who wasn't included.  Burnell has graciously stated that she "feels no bitterness toward the Nobel Committee," but in her place, I sure as hell would have.

The paper in Nature, however, describes an object that doesn't seem to fit any of the known types of electromagnetic pulses.  Called GPM J1839-10, it releases energy in the radio region of the spectrum.  But in terms of periodicity, it's somewhere between pulsars (which are so regular they've been proposed as celestial clocks) and fast radio bursts (which are apparently aperiodic).  GPM J1839-10 is slow -- its signal reaches a peak about every twenty-two minutes -- but it's not precisely regular.  The four hundred seconds centering on that twenty-two minute mark is when the peak is most likely to come, but sometimes the window will pass with no peak.  The length of the pulses is also variable, usually between thirty and three hundred seconds in length.  And unlike both fast radio bursts and pulsars, the amplitude of the peak is quite low in energy.

As science writer John Timmer put it in Ars Technica, "The list of known objects that can produce this sort of behavior... consists of precisely zero items."

What's weirdest is that going back through the records of astronomical observations, this object has been doing its thing for three decades, and only just now is attracting attention.  The astrophysicists thus far have no good explanation for what it might be.  It sits out there in space, slowly flashing on and off like some sort of interstellar lighthouse, and the the flat truth is that at the moment, no one has the slightest idea what it might be.

Of course, "We don't know" opens the door for a certain group of people to say "We do!"

As I've said before, no one would be more delighted than me if we did come across evidence of an extraterrestrial signal, but I strongly suspect this ain't it.  For one thing, the semi-regular blips it's putting out don't appear to contain any information; put a different way, the pattern isn't complex.  It could be a beacon, I suppose, but how you'd tell the difference between an alien-built celestial lighthouse and a star of some sort that is sending out pulses of radio waves is beyond me.  With nothing more to go on, by far the greater likelihood is that there is some natural explanation for this slowly-pulsing object -- we just haven't found it yet.

Even so, it's intriguing.  I've always loved a mystery, and this certainly is one.  It's possible that we've missed other objects of this type; the kind of detailed repeated scans of the sky in the radio region of the spectrum that it would take to detect a pulsation this slow have only begun to be done with any kind of thoroughness.  Like with Burnell's discovery of pulsars, it took finding others before astronomers had enough data to start putting together an explanation.

But if no others are found, what then?  It'll be added to the list of astronomical mysteries, of which there are plenty.  It's a big old universe, and filled with wonders, many of which we are only just beginning to understand.

And those are cool enough without the aliens.  Although, of course, I wouldn't object to the aliens as well.


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