A radio telescope has detected a fast radio burst from another galaxy that appears to pulsate in a regular 16-day cycle, according to a new paper on the pre-print server arXiv, which has not yet been peer-reviewed.

Nothing like this has been seen before. If these conclusions are on the money, it’s the first time that fast radio bursts have been documented repeating in a steady cycle. Before you ask, it’s probably not aliens. However, the observations could help to shed light on this deeply mysterious phenomenon.

Fast radio bursts (FRB) are intense blasts of radio emissions that generate as much energy in a millisecond burst as the Sun does in decades. Whatever is producing them must be unimaginably powerful, yet their origin remains unknown. Theories include evaporating black holes, a cataclysmic collision in the cosmos, and rotating celestial bodies, such as a highly magnetized neutron star. Some have suggested it could be signals from an advanced alien civilization, although that theory isn’t taken terribly seriously.

The first FRB was detected in 2007 through archived data recorded in 2001, so astronomers are still only just getting to grips with this curious phenomenon. Most FRBs have only been detected as ultra-brief energy bursts in a one-off event, although a few have been detected as a repeating event. This new discovery, however, seems to be a regularly repeating cycle.

The event, known as FRB 180916.J0158+65, appears to be coming from a spiral galaxy less than 500 million light-years away from Earth, making it the closest FRB discovered to date. The new research used the Canadian Hydrogen Intensity Mapping Experiment (CHIME) in British Columbia to record 28 bursts between September 16, 2018, and October 30, 2019.

This showed bursts every hour or so over the course of four days, before falling silent for 12 days. Then, the same pattern of activity would repeat again, creating a neatly packaged cycle lasting around 16.35 days.

“We conclude that this is the first detected periodicity of any kind in an FRB source,” they write in a paper. “The discovery of a 16.35-day periodicity in a repeating FRB source is an important clue to the nature of this object."

In theory, understanding the pattern of the cycle could give some hints of what’s producing the signals. For example, the cycle could be an indication of a celestial body’s rotation or an orbital period. However, for now, FRBs remain as mysterious as ever.