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For years, astronomers have been searching for patterns in strange blasts of radio waves coming from space. These fast radio bursts (FRBs) had seemed totally random, but for the first time we have seen an FRB that turns off and on again at regular intervals. Now we just need to figure out why.

FRBs are extremely powerful, flashing with the intensity of hundreds of millions of suns for just a few milliseconds. Most of them flash only once, but some so-called 鈥渞epeaters鈥� burst many times from the same location. We don鈥檛 know what causes them, although everything from hungry black holes and spinning pulsars to alien spaceships have been put forward as explanations.

Now, the Canadian Hydrogen Intensity Mapping Experiment (CHIME) has added another piece to the puzzle. In the past, the timing of bursts from repeater FRBs has seemed random, but CHIME has found one with a pattern. Over the course of 400 days of observations, all of the bursts arrived in four-day windows of about one burst per hour, followed by about 12 days without bursts and then another four-day window of activity. Researchers involved in CHIME declined to talk to 快猫短视频.

鈥淪uch a periodicity, if confirmed, would be the first smoking-gun signature [of any particular property of an FRB source], which points towards very likely orbital motion,鈥� says Bing Zhang at the University of Nevada, Las Vegas. For example, if two distant objects were orbiting one another once every 16 days, one of them could be emitting bursts all the time and we would only see them when the beam of radio aligned with Earth, producing the pattern seen by CHIME.

Other possible explanations include a spinning object or some sort of cloud between the FRB and us that periodically blocks it. But we have never found anything in space spinning that slowly while emitting such huge amounts of energy, and it is hard to imagine a cloud that clears out at such precise intervals.

So far, we haven鈥檛 found any other repeaters with a pattern anything like this, but that doesn鈥檛 mean that it is unique. We may have to observe other FRBs for years to be able to even look for periodicity effectively. 鈥淔or most repeating FRBs, we only have two or three pulses,鈥� says Emily Petroff at the University of Amsterdam in the Netherlands. 鈥淢aybe as we find more pulses from each repeater we can see if this source is representative.鈥�

This finding makes some of the models that astronomers have developed to explain FRBs less likely, says Leon Oostrum at the Netherlands Institute for Radio Astronomy. 鈥淢odels have been looking for randomness, because that鈥檚 what we鈥檝e been seeing so far from the other repeaters,鈥� he says. 鈥淢any of the more exotic models don鈥檛 predict any periodic behaviour, so I think this helps us narrow it down.鈥�

While we have detected more than 100 FRBs, we still have very few clues as to what they are, and every new clue seems to make them more confusing, says Oostrum. This new hint does at least make alien communications an unlikely explanation.

鈥淚f it were an alien beacon I would think it would emit more quickly, because a 16-day period is not efficient for communication,鈥� says Oostrum. 鈥淚magine getting one signal every 16 days 鈥� it would take forever to get a message.鈥�

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