Astronomers have spotted a mysterious radio signal relatively close to Earth that is behaving unlike anything observed before.
The low-frequency radio signal, located around 4,000 light-years away inside the Milky Way galaxy, appears once every 18 minutes or so and lasts between 30 and 60 seconds each time.
At times, the pulses are made of short-duration bursts less than a second in length, while other times they are smoother. In any case, the pattern of the radio source has "not been observed previously," its discoverers say in a report published online on Wednesday.
"It was kind of spooky for an astronomer because there's nothing known in the sky that does that," said Natasha Hurley-Walker, an astrophysicist at Australia's Curtin University node of the International Centre for Radio Astronomy Research, in a press release.
Radio signals from space are common occurrences particularly in the high-frequency spectrum due to energetic events like exploding stars. The low-frequency sky, however, is quieter.
The team's leading theory is that the source of the strange signal is a magnetar—a type of neutron star with an extremely intense magnetic field. Specifically, one that spins comparatively slowly.
Unexplained or unusual signals from space may naturally give rise to theories about aliens or other exotic phenomena. There have been numerous examples in recent years.
Fast radio bursts or FRBs often catch scientists' attention. These are bright radio bursts that last milliseconds and are speculated to come from high-energy astrophysical processes that are not fully understood. Some of them are one-offs while others repeat.
An FRB called FRB 180916.J0158+65 was discovered in February 2020, appearing several times per day for four days before falling silent for slightly more than 12 days. The overall 16-day-ish cycle could give an important clue to the nature of its source, scientists said at the time.
In September 2021, scientists said they had detected a mysterious radio signal that appeared to have come from the center of the Milky Way. Called ASKAP J173608.2-321635, the signal was detected six times between January and September 2020 and was dubbed "very strange" since it did not emit any other types of radiation other than a radio wave. Known astronomical objects would have emitted other radiation like high-energy X-rays at the same time, Newsweek was told.
Then there is the Wow! Signal, one of the most famous space signals ever detected. It was recorded in 1977 by the Big Ear Radio Telescope in Delaware, Ohio, and it surprised one of the astronomers that worked there so much that he circled the signal in a data print-out and wrote "Wow!" next to it, hence the name.
The Wow! Signal lasted for around 72 seconds and at the time caused a stir since it was a strong narrowband signal—a type that astronomers at the Search for Extraterrestrial Intelligence (SETI) organization had expected an alien signal to look like.
But the signal was never repeated despite astronomers' attempts to find it once again. Its source is still disputed.
here are clues that magnetars are behind at least some FRBs. In 2020, it was discovered that the magnetar SGR 1935+2154 was sending out radio waves consistent with FRBs in addition to X-ray radiation. At the time it was the first FRB seen from within the galaxy and showed that magnetars could produce these radio blasts.
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