Sunday, 20 January 2019

Repeating Fast Radio Bursts from Another Galaxy

Repeating Fast Radio Bursts from Another Galaxy

A recent paper in Nature has reported that the CHIME radio telescope, in the Okanagan area of British Columbia, Canada (which has only been operating for a short time), has already made several interesting and significant findings, with one that really stands out.

(Note that if you don’t know much about radio telescopes, or want to know more about them, especially CHIME, you can check out the sources at the end of the blog, including one of my earlier blogs about the Dominion Radio Telescope and one about transient astronomy, featuring Jocelyn Bell-Burnett, discover of the first pulsar.)

The findings that were reported relate to the discovery of several Fast Radio Bursts (FBRs), a phenomenon that this telescope is very well suited for, given its unique engineering and geometry.  Among the other Fast Radio Bursts that it has discovered, there has been a repeating FBR.  Previous to this discovery, there had only been one repeating FBR discovered.

Fast Radio Bursts really are fast – those that were reported in the paper (shown below) are sub-second events, with peaks that typically last well under a tenth of a second.  The signals from the repeating FRB are about 100 milliseconds (though the peak is much less), faster than the blink of an eye (which takes about 300 milliseconds).

But in that time, they seem to put out enormous amounts of energy, perhaps as much energy as our sun puts out in many years (maybe even a century).

The reason that we think these sources must be extremely energetic is that they seem to be located at enormous, cosmological distances.  That is inferred from something called the dispersion measure, in which the radio signal is delayed a tiny amount at different wavelengths.  As Jocelyn Bell-Burnett indicated in an earlier talk (referenced in my “Transient Astronomy” blog), this produces a sort of whistling effect.  For non-terrestrial signals, the pitch of the whistling depends on how much interstellar medium that the signal travelled through. Of course, astrophysicists don’t actually listen to the whistling, instead they detect it via computerized data analysis.

In the case of these Fast Radio Bursts, the amount of dispersion exceeds that which the galactic medium could produce, so they must be of extra-galactic origin.  In fact, the repeating FRB that was discovered by CHIME seems to come from about 500 million parsecs away (about 2 billion light-years).

So, the reasoning goes, for a signal of this strength to be detected from so far away, it must have come from a very energetic source.  A number of physical models have been proposed, though there is nothing even approaching a consensus on the subject.

One theory says that the amount of energy being released must be indicative of a hugely catastrophic cosmic event, such as the collapse of a star into a black hole, or the collision of two neutron stars.  But, obviously the finding of a second repeating Fast Radio Burster makes those explanations untenable, at least for the repeating FBRs.  After all, a gravitational collapse or a collision of two very compact objects such as neutron stars can only happen once, so the fact that the event repeated six times over a few months rules those models out, at least for the source recorded by CHIME.

Some other models that have been proposed involve objects such as neutron stars, especially those highly magnetic ones known as magnetars.  The fact that the radio waves have been highly polarized indicate that they must have been affected by a very strongly magnetized plasma, such as that associated with a magnetar.  The paper notes that “a shocked, highly relativistic plasma outside a compact object might explain the behaviour seen in the FRB’s bursts”.

The repeating FBR in question (FRB 180814.J0422+73) seems to have had six bursts over a period of about six weeks.  Of course, those are only the bursts that we happened to detect – most of the time the source was not within the telescope’s field of view.  In fact, calculations show that it was probably only within the telescopes field of view for about 23 hours during this six month period, so it likely had a lot more bursts than just six during this six weeks.

Another possibility is that these events don’t actually pack the amount of energy that has been calculated, because they are beamed energy sources rather than sources that emit energy in all directions.  If that was the case, Earth would have to be positioned in just such a way as to detect the beam. That would imply that there were a lot of these events, or at least that there were a lot of these events at some time, as the odds of Earth being within the beam of any particular source are very small, depending on how tight the beam is.

There have been some exotic speculations, involving extra-galactic civilizations.  Of course that wouldn’t mean that aliens from far-off galaxies are using these signals to contact Earth, or even the Milky Way.  Since the radio signals took billions of millions of years to traverse inter-galactic space, such a communication would be the ultimate in “call waiting”.  However, it has been conjectured that these could be some leakage from a different activity, say a spaceship being accelerated to great speeds (the fabled warp drive?).  In that case, it would be as if we were intercepting a small random sample of take-offs and landings from some extra-galactic spaceport.  Of course, these are fun speculations – more likely it is something fantastic, but nonetheless natural.

And if you want a general idea of where this object is in the sky, see below (my estimate, based on the reference given by the naming convention):

CHIME - An array of four cylindrical reflector antennae, each 100 meters long and 20 meters wide.  They are being used in an experiment to measure the cosmological red-shift of the 21-cm line of neutral hydrogen, which will give us a better idea of the history of the expansion of the universe itself.

Main Radio Telescope Dishes at the Dominion Observatory


The CHIME/FRB Collaboration. A second source of repeating fast radio bursts. Nature
018-0864-x (2019).

As it turns out, I have written two blogs that touched on these subjects.  One was about a visit to the radio telescope in question.  It has some explanation of radio telescopes in general, as well as the CHIME telescope in particular.
The other was about a talk given at the University of Alberta by Jocelyn Bell-Burnett, who discovered the first pulsar.  Her talk was about “transient astronomy”, which includes Fast Radio Bursts.
Transient Astronomy – Bursts, Bangs and Things that Go Bump in the Night (Jocylen Bell Burnell Lecture):
Dominion Radio Astrophysical Observatory:
Arecibo Radio Telescope:
Manasvi Lingam1, 2 and Abraham Loeb2.   Harvard University, Cambridge, MA.  The paper reporting this work has been accepted for publication in the Astrophysical Journal Letters.

I also want to thank my son Scott, for discussions on this subject, as he has a PhD in astrophysics, with a focus on magnetars.  In fact, he got his PhD under one of the authors of the paper.  He now works in the data science field, because it pays better.  😀


Now that you have read some real science (astronomy and astrophysics), you should read some science fiction.  Either of the Kati of Terra series or the Witch’s Stones series would be excellent choices.  Alternatively, you could try the short story “The Magnetic Anomaly”, which has lots of physics, and plenty about magnetic fields. 😀

Kati of Terra

How about trying Kati of Terra, the 3-novel story of a feisty young Earth woman, making her way in that big, bad, beautiful universe out there.  

The Witches’ Stones

Or, you might prefer, the trilogy of the Witches’ Stones (they’re psychic aliens, not actual witches), which follows the interactions of a future Earth confederation, an opposing galactic power, and the Witches of Kordea.  It features Sarah Mackenzie, another feisty young Earth woman (they’re the most interesting type – the novelist who wrote the books is pretty feisty, too).

The Magnetic Anomaly: A Science Fiction Story

“A geophysical crew went into the Canadian north. There were some regrettable accidents among a few ex-military who had become geophysical contractors after their service in the forces. A young man and young woman went temporarily mad from the stress of seeing that. They imagined things, terrible things. But both are known to have vivid imaginations; we have childhood records to verify that. It was all very sad. That’s the official story.”