FRBs: Mystery Radio Signals From Deep Space Might Be Being Blocked on Way to Earth

An artist’s impression of CSIRO’s ASKAP radio telescope detecting a fast radio burst (FRB). Scientists learned that they did not appear in lower frequencies, potentially making the cosmological phenomena even more bizarre. OzGrav, Swinburne University of Technology

Scientists studying mysterious radio signals coming from deep space discovered something "really unexpected"—that they did not appear in lower frequencies, potentially making the cosmological phenomena even more bizarre.

Fast radio bursts (FRBs) are signals emanating from an unknown source in deep space. The first FRB was discovered in 2007, and dozens more have been documented since then. They appear to come from extremely high-energy events, but because they last just a few milliseconds, determining their origin has been difficult.

So far, scientists have traced one FRB to a dwarf galaxy 3 billion light-years away. This FRB was unusual in that it was found to repeat, meaning scientists could monitor it to try to determine its source. All other FRBs recorded appear to be one-off events—this makes understanding them extremely difficult.

In a study published in the Astrophysical Journal, a team of researchers led by Marcin Sokolowski from Australia's Curtin University have now learned that FRBs are not observed at lower frequencies.

The team pointed two telescopes at one patch of sky—the Murchison Widefield Array (MWA) and CSIRO's Australian SKA Pathfinder (ASKAP) telescopes. The latter was recently used to find dozens of FRBs, the findings of which were published in the journal Nature. But while ASKAP was recording new FRBs, the MWA telescope didn't pick up on anything.

"When ASKAP sees these extremely bright events and the MWA doesn't, that tells us something really unexpected is going on; either fast radio burst sources don't emit at low frequencies, or the signals are blocked on their way to Earth," Sokolowski said in a statement.

Explaining what could be meant by "being blocked," Sokolowski told Newsweek: "This is another possibility that low radio-frequency signals are either absorbed or scatter as they travel from the source of the FRB to Earth. Low frequencies are more affected by these kind of processes so there is a possibility that high frequencies travel from the source of the FRB to Earth, but low frequencies are absorbed or scattered on their way.

"The term 'blocked' was used to cover both these possible processes (absorption and scattering). We don't really know what happens yet whether the low radio-frequencies are not emitted by the source of the FRB or they are absorbed right at the source or absorbed / scattered along their way from the source of the FRB towards Earth. Our results indicate that scattering, which results in broadening of FRB pulses in time and makes them much longer at lower frequencies and therefore covering longer time, is insufficient to explain the MWA non-detections."

An artist’s impression of fast radio bursts (FRBs). OzGrav, Swinburne University of Technology.

He said their findings do not point to any specific source, but that the research "adds some new pieces to the FRB puzzle."

Jean-Pierre Macquart, co-author of the study, said: "It's really thrilling to have a clue about the origins of these incredible bursts of energy from outside our galaxy.The MWA adds an important piece of the puzzle, and it was only made possible with this "technological tango"between the two telescopes.

"It's an exciting development because it unites the two teams and it brings home the advantage of having the two telescopes at the same site. Future coordination between the teams will also benefit other areas of astronomy, as complementary views from the two telescopes can provide a more complete picture of a situation."

So far, only one low-frequency FRB has been detected. This discovery was announced in The Astronomers Telegram in August. According to Scientific American, low-frequency FRBs are important as scientists will be able to use them to better understand how they interact with interstellar matieral.

In terms of what could be producing FRBs, several theories have been put forward, including black hole mergers, imploding pulsars and collapsing neutron stars.

Ryan Shannon, from Swinburne University of Technology, Australia, was part of the team that discovered FRBs using the ASKAP telescope. He recently told Newsweek what he thought was behind these mystery bursts: "The energies associated with FRB production are enormous, making the processes that cause them very different than what we observe locally. Neutron stars, in particular highly magnetized neutron stars, might be the favored origin, because we see vaguely similar emission from neutron stars in our own galaxy, but it is a trillion times less intense than what FRBs produce. We'll need to find more to confirm the cause of FRBs. We'll also need a better theory for how to produce them, given the enormous amount of energy in the events."

This story has been updated to include quotes from Marcin Sokolowski.