Astronomers have just found 25 more mysterious, repeating radio signals from space

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Repetitive rapid radio bursts remain a mystery to astronomers, but these new discoveries could lead to important answers about them, as well as provide insight into other mysteries of the cosmos.

Fast radio bursts, or FRBs, are short, powerful pulses of radio waves detected from space. Some can last up to three seconds, while others appear and disappear in a fraction of a millisecond. However, their origin is a mystery. Given the amount of energy they carry, researchers speculate that they are produced by some of the most energetic events in the universe – supernovae, gamma-ray bursts, or collisions between neutron stars, pulsars, or black holes. The only thing that is known for sure is that most FRBs come from outside our galaxy.

Fast Radio Bust - Artist's Rendering - eso1915a — Fast Radio Bust – Artist’s Rendering – eso1915a

This artist’s impression shows a fast radio burst traveling from its source in a distant galaxy (upper left) to Earth in the Milky Way (lower right), crossing the halo of a massive galaxy. Credit: ESO/M. grain knife

It has been over 15 years since the first FRB was discovered from space. Hundreds more have been found in that time, but astronomers are no closer to the exact cause.

Even more puzzling are the few FRBs found that repeat periodically. So far, out of hundreds of FRBs discovered, only 25 belonged to a specific class known as repetitive FRBs.

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Find what has been missed

In new research, a Canadian-led team of astronomers has discovered another 25 repeating FRBs, doubling the number already discovered.

The researchers found them by conducting the first-ever examination of all data collected between September 2019 and May 2021 by the Canadian Hydrogen Intensity Mapping Experiment. CHIME is a unique, highly sensitive radio telescope at the Dominion Radio Astrophysical Observatory near Penticton, British Columbia, located on traditional ancestral and unceded Syilx/Okanagan territory.

The CHIME radio telescope’s four “cylinders” are firmly in place, staring up at the sky from the floor of the Okanagan Valley in southern BC. Photo credit: CHIME Collaboration

“Many seemingly one-off FRBs have simply not been observed long enough to detect a second burst from the source,” said Dr. Ziggy Pleunis, a postdoctoral researcher at the University of Toronto’s Dunlap Institute for Astronomy and Astrophysics, who is one of the nearly 60 scientists involved in this new study.

“We need a longer observation period because some repeaters could repeat every 10 years. We just don’t know. They don’t play on our timescales,” added co-author Adam Dong, a Ph.D. Student in the Faculty of Physics and Astronomy at the University of British Columbia.

Of the 25 newly discovered repetitive FRBs, most were discovered two or three times during the CHIME observations. During the same time, one of them – FRB 20201124A, first discovered in 2020 and coming from a nearby galaxy – has been observed a total of 12 times!

Repeating Fast Radio Bursts Locations Northern Sky CHIME FRB

Taken from the new research study, this sky map shows the locations of every repetitive rapid radio burst detected so far. Credit: CHIME/FRB Collaboration/The Astrophysical Journal

To filter out these signals, the team had to develop new statistical tools to sift through the data from CHIME.

“We can now accurately calculate the probability that two or more bursts coming from similar locations are not just coincidence,” explained Pleunis. “These new tools were essential for this study and will also be very useful for similar future research.”

One of the challenges of studying FRBs is that there is no predicting when one will appear. In most cases, astronomers can only point their radio telescopes at the sky and hope to pick up one or more of these signals during their observing time. Some researchers have predicted that thousands could fly across the sky every day. However, we only detect a small number due to the limited amount of sky that current radio telescopes can scan at any one time.

Finding repeating FRBs is even harder. This is because radio telescopes must be pointed at the same part of the sky for each repeated signal. So without knowing the timing of the reps, it becomes even more dependent on luck.

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CHIME sweeps for FRBs

Operating since 2017, CHIME observes the entire sky above at once and is ready to intercept any signals from space that appear in its field of view. While optical telescopes usually have to wait until dark, radio astronomy can be done day or night. So, as the Earth rotates, CHIME can roam the entire northern half of the celestial sphere each day.

In the first year alone, CHIME collected over 500 FRBs. By mid-2020, the telescope had spotted well over 1,000, according to the CHIME Collaboration.

See below: A full day’s time-lapse of CHIME observations

CHIME is an excellent tool for detecting FRBs, but it has its limitations. Because it’s tied to the Earth’s rotation, the telescope’s field of view sweeps around space, a bit like the cone of light from a lighthouse. So although it can cover the entire northern celestial sphere in a day, it depends on how many FRBs it detects and how many repeating FRBs it finds, exactly what part of space it’s currently observing. If the timing of an FRB—repetitive or not—is shifted by even the smallest amount such that the source is below CHIME’s horizon when the signal arrives here, the telescope will still miss it.

However, if there were more telescopes like CHIME, astronomers could cover much more space at once, capturing many more FRBs and discovering more repeats.

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Why is that important?

The researchers believe their new techniques will help find even more repeating FRBs. Other telescopes can then observe these discoveries at just the right time to pick up the repeat signals.

“FRBs that repeat make great targets for other telescopes, including ones that can measure their positions very accurately and let us know which galaxies they come from,” said co-author Dr. Ingrid Stairs, a professor in the University of British Columbia’s Department of Physics and Astronomy, according to UBC News. “In the long term, we hope to learn a lot about their origins.”

“FRBs are likely produced from the remnants of the explosive death of stars.” said Pleunis, referring to neutron stars, pulsars and black holes, or phenomena like gamma-ray bursts. “By studying repetitive FRB sources in detail, we can study the environments in which these explosions occur and better understand the final stages of a star’s life. We can also learn more about the material that is ejected before and during the star’s demise and then returned to the galaxies where the FRBs live.”

Also, detecting more repeating FRBs can help astronomers find answers to other questions about the universe.

“An exciting line of research is using them to measure the amount of matter between galaxies or the intergalactic medium,” explained Adam Dong in the UBC press release.

In addition to the 25 confirmed repeat FRBs found in this study, the researchers identified an additional 14 possible candidates. While there were significant differences between repeated bursts—in position, spread, timing, etc.—for these candidates, if they can be confirmed as actual repeaters, it could reveal even more about these mysterious phenomena.