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What explains the fascinating radio bursts from outer space

You've seen the movie. A weary radio astronomer is sitting in a control room full of complex electronics, wi...

Posted: Jan 11, 2019 3:44 AM
Updated: Jan 11, 2019 3:44 AM

You've seen the movie. A weary radio astronomer is sitting in a control room full of complex electronics, with an earphone held sleepily against her ear. She hears a crackle, then another and another, until the unmistakable sound of a radio transmission is heard. Jolted alert, she checks known frequencies and finds that nothing should be there.

And yet it is. She grabs the red telephone and calls the President, telling him that the first radio transmission from an extraterrestrial intelligence has been received. Usually the plot unfolds with invasions and explosions.

Extraterrestrial life

Space and astronomy

So, that sort of just happened.

But that "sort of" is important, because it's rare that real science neatly follows a script that can be packed into a two-hour movie. Let me tell you the real story.

Astronomers working at a Canadian radio telescope have reported the observation of fast radio bursts or FRBs. Even more exciting, one FRB has been reported to repeat six times at the same location. This is uncommon and is why those who believe in the existence of extraterrestrial civilizations are so excited.

But it would be hasty to jump from this scientific triumph to the conclusion that ET is trying to contact us.

Here's what we do know.

FRBs are very short and extremely high-power bursts of radio energy that we detect in our telescopes here on Earth. They typically last only a few milliseconds and are usually broadband (which means they cover a range of frequencies). The burst is generally a single spike of energy, which is stable and constant over its brief duration.

FRBs are also a relatively recently-discovered phenomenon, first observed in 2007. They are observed everywhere in the sky and are not concentrated in the plane of our Milky Way galaxy. Combined with some technical observations of the precise time of arrival of different frequencies, this uniformity heavily points to an extragalactic origin. Whatever is causing FRBs, it is unlikely that they are emitted from within our galaxy.

The most recent announcement has been made by the CHIME (Canadian Hydrogen Intensity Mapping Experiment) radio telescope, located in the hills of British Columbia. Prior to the announcement, 50-60 FRBs had been observed and only one that had repeated itself. CHIME added 13 additional FRBs and a second repeater.

The low number of observed FRBs is probably due to limitations of the instrumentation. Earlier FRBs were observed at somewhat higher frequencies, while the CHIME telescope was able to look at frequencies in the range of 400 MHz. The next lowest one was at 700 MHz.

It's also worth noting that the CHIME observatory is in the commissioning phases and is not operating at full sensitivity. When the facility is performing according to expectations, it is likely that it could observe many dozens of FRBs per day.

In spite of some of the more breathless media reports that you will encounter, astronomers do not believe that FRBs are attempts by aliens to contact us. First, they appear spread across the entire sky -- with individual sources sometimes located billions of lightyears away from one another.

Second, it's just far more likely that FRBs have a natural origin. Because of the short (few millisecond) duration, it seems likely that the source is no larger than a few hundred kilometers in size. If the sources are of extragalactic origin and hundreds of millions of light hears away, they must be incredibly energetic, perhaps releasing in a few milliseconds the same amount of energy our sun releases in 10 to 100 years.

So, what are they? Frankly, we don't know. Some astronomers have proposed that they are due to the merging of neutron stars. Others have proposed that they are the result of the flares emitted by magnetars, which are highly magnetic neutron stars. This idea is similar to familiar solar flares, but much more energetic. Others have suggested that perhaps FRBs are due to a black hole converting into a white hole and exploding. Even more exotic explanations involve the collision of cosmic strings -- proposed remnants of the Big Bang.

At this point, the scientific community doesn't have a firm answer, but this most recent measurement adds critical information to the conversation. Most proposed explanations for FRBs are things that happen just once (like the merging of two stars).

The existence of two FRB sources that seem to be repeaters suggests a different origin. Something that happens again and again is more like the magnetar hypothesis. But it's going to take more data (and more thinking) to figure out just what the source is.

Because CHIME is just getting started, our understanding of FRBs is in the preliminary stages. This is always the case when new scientific facilities begin operations. Data and knowledge start with a trickle, with the flow increasing until scientists are deluged with information. It's likely that in a few years we will have a new appreciation of an interesting astronomical phenomenon.

And for those who really like the idea that FRBs are of extraterrestrial origin, it's probably worth remembering the cautionary tale of Jocelyn Bell Burnell, who discovered a different source of extraterrestrial radio waves back in 1967. She also heard a radio source in her instrumentation, and people didn't know what to make of it. Because of the uncertainty, her radio sources were briefly called LGM, short for "little green men." But, in the fullness of time, she had discovered pulsars, which are quickly rotating neutron stars.

Speculation is fun, but real science is far more informative. Let's give the astronomers a bit more time to discover how our universe works.

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