This is how scientists tracked down the location of a fast radio burst and confirmed that these short but spectacular flashes of radio waves originate in the distant universe. (Commonwealth Scientific and Industrial Research Organization (CSIRO))

Astronomers have been perplexed by Fast Radio Bursts (FRBs) for over a decade, but now at least part of the mystery has been solved. In a study published Wednesday in Nature, researchers report for the first time the actual source of one of these strange bursts – or the location of the source, anyway.

First, a little bit about FRBs: They're bright radio flashes of the flash-in-the-pan variety, lasting just a few milliseconds and never repeating. Scientists believe they must occur thousands of times a day, but until this most recent study, only 16 had ever been detected. They seem randomly distributed throughout the sky, and no one is sure what causes them.

What is causing these strange radio signals?

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Now, thanks to the new study, we at least know where one of them came from. A flash detected on April 18 by the Commonwealth Scientific and Industrial Research Organization's (CSIRO)  64-m Parkes radio telescope in Australia was tracked down to an elliptical galaxy around 6 billion light years away. The flash, known as FRB 150418, was pinpointed thanks to a quick-response-system set up by lead author Evan Keane and colleagues. 

"In the past FRBs have been found by sifting through data months or even years later," Keane, an astronomer with the Square Kilometer Array Organization, said in a statement. "By that time it is too late to do follow up observations."

But these days, a ping on the Parkes radio telescope sets off a flurry of email alerts, allowing scientists to get straight to work.

"I was awoken by my phone going crazy a few seconds after it happened, saying: Evan, wake up! There was an FRB!" Keane told the BBC.

That allowed the team to turn immediately to the Australia Telescope Compact Array – and they were able to catch the FRB's afterglow. Then yet another telescope – the Subaru telescope in Hawaii – was used to image the source galaxy itself. Once they had an optical look at the host galaxy, they could use its light to calculate its distance.


A zoom-in of an elliptical galaxy showing the FRB pulse detected at Parkes. The ATCA observations allow us to pinpoint which galaxy the FRB came from.
(David Kaplan & Dawn Erb)

We still don't know what causes FRBs, but this does give us some clues: As Slate's Phil Plait points out, elliptical galaxies are usually quite old. That means it's unlikely that a massive star going supernova caused this particular FRB, since stars like that don't tend to live long enough to show up in galaxies this decrepit.

Based on the suspected age of the galaxy and the timescale of the event (the afterglow lasted six days) the researchers believe a pair of colliding neutron stars could be to blame. But it's possible – even likely – that FRBs come from a variety of sources, because some of the previously observed bursts didn't seem to fit the same bill.

FRBs may still hold many mysteries, but they're already being put to use: Scientists can use them to calculate the distribution of matter in the universe. FRBs are distorted as they pass through matter, meaning that some frequencies of the signal arrive a little sooner than others. Based on the delay, scientists can calculate how many particles of space gas and dust the wave went through on its journey.

"Until now, the dispersion measure is all we had," CSIRO's Simon Johnston, co-author of the study, said in a statement. "By also having a distance we can now measure how dense the material is between the point of origin and Earth, and compare that with the current model of the distribution of matter in the Universe. Essentially this lets us weigh the Universe, or at least the normal matter it contains.”

And guess what? The new weigh-in managed to find a whole bunch of matter that had been "missing" up until now. It's thought that the universe is made up of 70 percent dark energy, 25 percent dark matter and 5 percent boring-old-normal matter, but around half of the latter has never been measured directly.

You read that correctly: Only 5 percent of the universe's matter is stuff we understand, and half of that we've failed to detect. Do you feel small? I feel small. 

"The good news is our observations and the model match, we have found the missing matter," Keane said in a statement. "It's the first time a fast radio burst has been used to conduct a cosmological measurement."

Three highly sensitive FRB-detecting instruments are set to open this year. If scientists can keep up the quick footwork accomplished by Keane and his team, FRBs won't be mysterious for very much longer.

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