Mystery cosmic radio bursts pinpointed
They're one of the most persistent puzzles in modern astronomy.
As the name suggests, Fast Radio Bursts (FRBs) are short-lived - but powerful - pulses of radio waves from the cosmos.
Their brevity, combined with the fact that it's difficult to pinpoint their location, have ensured their origins remain enigmatic.
Outlining their work at a major conference, astronomers say they have now traced the source of one of these bursts to a different galaxy.
It's an important step to finally solving the mystery, which has spawned a variety of different possible explanations, from black holes to an extra-terrestrial intelligence.
The first FRB was discovered in 2007, in archived data from the Parkes Radio Telescope in Australia. Astronomers were searching for new examples of magnetised neutron stars called pulsars, but found a new phenomenon - a radio burst from 2001. Since then, 18 FRBs have been found in total.
"I don't exaggerate when I say there are more theories for what these could be than there are observed bursts," first author of the new study, Shami Chatterjee, told the BBC's Science in Action programme.
All FRBs were found using single-dish radio telescopes that are unable to narrow down the sources' locations with enough precision to further characterise the flashes.
But Dr Chatterjee, from Cornell University, New York, and colleagues used a multi-antenna radio telescope called the Very Large Array (VLA), which had sufficient resolution to precisely determine the location of a flash known as FRB 121102.
Unlike all the others, this FRB - discovered in 2012 - has recurred several times.
"When we reported last year that one of these objects was repeating, that - in one go - knocked out about half of those models, because for this one source, at least, we knew it couldn't be explosive. It had to be something where the engine that produced this survived for the next flash."
In 83 hours of observing time over six months in 2016, the VLA detected nine bursts from FRB 121102.
"We now know that this particular burst comes from a dwarf galaxy more than three billion light-years from Earth," said Dr Chatterjee.
"That simple fact is a huge advance in our understanding of these events."
Prof Heino Falcke, who had investigated FRBs, but was not involved in the latest study said that, even without a clear answer, the new findings were a "game changer". But he admitted several features associated with FRB 121102 remained mystifying.
In a viewpoint article published in Nature he said: "To me, the radio spectrum and variability of the authors' source look a lot like the low-power black holes that I have studied over the past 25 years."
"But if this were true, most astronomers would have expected a bright galaxy to be present, because large black holes are typically found only in large galaxies. It is therefore utterly confusing that the faint optical source coincident with the persistent radio source can at most be a small 'dwarf' galaxy, if it is a galaxy at all."
Further research will be needed to clarify the nature of the flashes, and to determine whether all FRBs are caused by the same phenomenon - or have different causes.
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