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A mysterious radio burst is helping astronomers probe the structure of the Universe

Another fast radio burst strikes again

CSIRO's Parkes radio telescope
CSIRO/Shaun Amy

Astronomers have detected another mysterious flash of radio waves originating from deep space — and it’s the brightest one found to date. This is the 18th fast radio burst, or FRB, that’s ever been found, and while researchers still don’t know exactly what causes these odd flashes, the source of this particular FRB has been narrowed down more precisely than ever before.

Such precision has allowed astronomers to use this FRB as a kind of probe to measure the swirling matter that lies between galaxies. The researchers were able to figure out the density and turbulence of all the intergalactic particles that lie between Earth and the source of the burst, as well as the magnetic fields of this “cosmic web.” This information could give us a better understanding of the stuff that forms galaxies, as well as how our entire Universe is structured.

“This FRB does represent a very clean way of probing intergalactic space,” Vikram Ravi, lead author of today’s Science paper detailing the FRB’s discovery, tells The Verge.

FRBs have been an enigma for astronomers ever since the first one was detected in 2001. These flashes usually last for just milliseconds at a time, and they seem to come from somewhere deep outside the Milky Way Galaxy. Though we’ve only found just over a dozen of these bursts so far, astronomers think thousand of them go off over the sky every day. And no one can seem to agree exactly what causes them. Some have speculated that colliding neutron stars may be to blame, but a consensus hasn’t been reached — and it’s possible that multiple types of events are responsible for these burst.

“We really don’t know where they come from, which particular galaxies [they start in], or even what causes them and how they’re emitted,” says Ravi.

The narrowed down location of the FRB.
Dr. Vikram Ravi/Caltech and Dr. Ryan Shannon/ICRAR-Curtin/CSIRO

What we do know is that these radio waves occur at gigahertz frequencies — the same frequencies that cell phones use — and we’ve created telescopes that can pick up these signals fairly well. One of them is the CSIRO Parkes radio telescope in Australia. While using this telescope to observe a pulsar, one of the study authors decided to turn on the telescope’s real-time FRB detector, and serendipitously picked one up. The flash was so bright that it lit up multiple pixels in the detector, whereas typical FRBs only light up just one.

Because this FRB was so high energy, the research team was able to pinpoint its position in the sky incredibly well. They think the burst is one of the closest FRBs ever found, even though it originated roughly a billion light years away. And there a few possible galaxies that may have been the source of this signal; the top candidate is a galaxy called VHS7 but it’s hard to know for sure.

That means this discovery won’t be solving any mysteries about what causes FRBs or where they come from. But since the researchers were able to refine the burst’s position so well, they were able to use it as a tool for measuring all the stuff that lies between us and the FRB. Astronomers think that a good portion of all the luminous matter in the Universe exists as plasma in the space between galaxies. This material is fairly hot and dispersed throughout space, but its light is so weak that it’s hard to see in optical or ultraviolet wavelengths.

The plasma does affect how we receive FRB signals here on Earth, though, by delaying the time it takes for the light to reach us. By measuring this delay, the astronomers were able to figure out the density of all the plasma along the FRB’s line of sight. And by observing how the FRB’s light was distorted as it moved through space, they figured out the plasma wasn’t very turbulent. Finally, they found that the plasma’s magnetic field was very weak.

The frequency of the FRB waves by color.
Dr. Vikram Ravi/Caltech and Dr. Ryan Shannon/ICRAR-Curtin/CSIRO

Ravi claims that an FRB has never provided such a wealth of information regarding the intergalactic medium before. “This is the first time we’ve had such a confluence of measurements,” Ravi says. It’s thought that this plasma is crucial for forming galaxies and structuring the Universe, so astronomers are really curious about the behavior of the cosmic web. Knowing how it operates in space can tell us a lot about how the Universe evolved, and today’s study suggests that FRBs may be useful in probing the cosmic web further.

“It shows the promise of probing the large-scale structure of the Universe,” Duncan Lorimer, an astrophysicist at West Virginia University who was not involved with this research, tells The Verge. “This particular source doesn’t solve the mystery of what [FRBs] are. But it gives us a great amount of hope for what they can do in the future.”