Fast radio bursts (FRBs) are perhaps the most mysterious anomaly in space, with many having unknown origins. According to a new study, an FRB has been spotted coming from a galaxy 500 million light-years from Earth and it's repeating every 16 days.

And no one knows why.

Known as FRB 180916.J0158+65, this FRB sends out radio wave bursts for a period of four days, stops for a period of 12 days, then repeats itself. The initial 28 patterns were first observed between September 2018 and October 2019, according to a pre-published study. "We conclude that this is the first detected periodicity of any kind in an FRB source," the researchers wrote in the study.

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“The found location is radically different from the previously located repeating FRB, but also different from all previously studied FRBs," said Kenzie Nimmo, a doctoral student at the University of Amsterdam, in a statement. “The differences between repeating and non-repeating fast radio bursts are thus less clear and we think that these events may not be linked to a particular type of galaxy or environment. It may be that FRBs are produced in a large zoo of locations across the universe and just require some specific conditions to be visible.”

It's unclear what's causing the pattern to repeat, but the study's abstract suggests there is "a mechanism for periodic modulation either of the burst emission itself, or through external amplification or absorption, and disfavor models invoking purely sporadic processes."

The FRB has been traced to a galaxy known as SDSS J015800.28+654253.0 and despite its great distance from Earth, at 500 million light-years, it is the closest FRB detected so far. A light-year, which measures distance in space, equals 6 trillion miles.

It's possible the FRB could be orbiting a compact object, for example, a black hole, causing its pattern to repeat, the researchers added in the study. It's also possible that it could be coming from a binary star system, but more research is needed.

It's unknown how common FRBs actually are and why some of them repeat and others do not; most of their origins are also mysterious in nature.

Some researchers have speculated they stem from an extraterrestrial civilization, but others, including the Search for Extraterrestrial Intelligence Institute, or SETI, have said that explanation "really doesn't make sense."

They come from all over space "and arranging cooperative alien behavior when even one-way communication takes many billions of years seems unlikely — to put it gently," SETI wrote in a September 2019 blog post.

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First discovered in 2007, FRBs are relatively new to astronomers and their origins are mysterious. According to ScienceAlert, some of them can generate as much energy as 500 million suns in a few milliseconds.

In July 2018, an FRB that hit Earth was nearly 200 megahertz lower than any other radio burst ever detected.

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