Mysterious radio bursts coming from deep space

The bevy of high-speed flashes came from 1.5 billion light-years away, and they include one exceedingly rare repeating burst.

By Shannon Stirone
Published 10 Jan 2019, 09:12 GMT
Stars hang over the Canadian Hydrogen Intensity Mapping Experiment, or CHIME, at the Dominion Radio Astrophysical ...
Stars hang over the Canadian Hydrogen Intensity Mapping Experiment, or CHIME, at the Dominion Radio Astrophysical Observatory in Kaleden, British Columbia.
Photography by Andre Renard

Astronomers have detected 13 high-speed bursts of radio waves coming from deep space—including one that regularly repeats. While the exact sources remain unknown, the new bevy of mysterious blasts does offer fresh clues to where and why such flashes appear across the cosmos.

Fast radio bursts, as they are known to scientists, are among the universe's most bizarre phenomena. Each burst lasts just thousandths of a second, and they all appear to be coming from far outside our home galaxy, the Milky Way.

Since these bursts were discovered in 2007, their cause has remained a puzzle. Based on estimations of the known range of their frequencies and an understanding of activity in the universe, scientists expect that nearly a thousand of them happen every day. But to date, only a handful have been found.

Now, a team using the Canadian Hydrogen Intensity Mapping Experiment, or CHIME, has announced the additional 13 new detections, including an especially rare repeating burst. Until now, only one other repeating fast radio burst was known to exist.

“The repeater,” as it being called, and its 12 counterparts came from a region of space some 1.5 billion light-years away, the team reports today in the journal Nature. All 13 new bursts have the lowest radio frequency yet detected, but they were also brighter than previously seen fast radio bursts, leading the team to think the low frequency has something to do with the sources’ environment.

“It doesn't mean that they're travelling from further away,” says study author Shriharsh Tendulkar, a postdoctoral fellow in the department of physics at McGill University. “As light propagates through the hot gas and plasma in the intergalactic medium and the interstellar medium, it has a bunch of different effects on the signal.”

For instance, the radio waves get twisted as they travel through space and can scatter or be absorbed by gas and plasma. The team therefore thinks that all 13 bursts probably originated from dense, turbulent regions inside their host galaxies, particularly areas with a lot of violent activity, such as near dense supernova remnants or close to black holes.

Deepening mystery

Tendulkar and the team also noticed that the structure of the new repeating burst is strikingly similar to the only other repeater ever found.

“The fact that we see these multiple structures in the burst was very similar to the first repeating fast radio burst. This is very uncommon,” he says. “Now there is this tantalising evidence that these bursts’ structures are seen only in repeaters.” That suggests that if more fast radio bursts are found with that structure, they may be prime candidates for also being repeaters.

The new repeating burst is brighter than the previous detection, which might be due to the fact that it is 1.5 billion light-years closer, but the team can’t know that for sure. To draw more comparisons, they’ll have to search the skies for the new burst’s host galaxy, which is not a guaranteed find. In the meantime, the team is continuing to use CHIME to observe the region of the sky where these bursts came from, as well as using other radio telescopes to follow up on the finds.

“We are trying to build up clues and trying to understand whether the repeating fast radio bursts and single fast radio bursts are different populations,” Tendulkar says. “Do they come from different objects? Or are they related in some way to each other? We are trying to figure these things out, so that's really exciting.”

What’s more, when CHIME detected these new bursts, it was only running at a fraction of its capacity, and the team is excited to see how many more will appear in their data now that the instrument is fully up and running.

“The CHIME discovery points to a huge potential,” says Shami Chatterjee, a senior researcher at the Cornell Center for Astrophysics and Planetary Science who was not involved in the latest discoveries. “I’m intensely curious how many [fast radio bursts] they are sitting on now. They must have dozens or hundreds.”

Finding yet more bursts means that the odd occurrences could be effective tools for understanding the traces of gas, dust, and plasma that exist in the seemingly empty space between galaxies, called the intergalactic medium, Chatterjee adds.

“Everyone agrees that in the intergalactic medium, it's very hard to have a probe that can tell you about its make up,” Chatterjee says. “It is orders of magnitude emptier than our own interstellar medium, but because of the [fast radio bursts] that we are now finding, it is going to be one of the few ways that we can probe this medium and understand those environments.”

And for now, Tendulkar notes that the mystery surrounding fast radio bursts remains part of their appeal.

“There is a lot of fun in the not knowing,” he says. “You keep adding more information, but as in all sciences, whenever you solve one mystery, it always opens up three more.”

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