Astronomers have detected alien signals – that is, signals from a foreign galaxy – being emitted in an unusually regular 16-day cycle.

Fast radio bursts (FRBs) are not in and of themselves unusual – the first was detected in 2007 – but previous observations have shown them to be mostly emitted at random.

While there have been some bursts which repeated, as astronomers discovered previously, they have never been seen repeating in such a steady cycle.

The origin of FRBs hasn’t been established yet, although the dominant theories regarding them suggest the signals are produced by rapidly rotating bodies such as neutron stars or black holes.

Researchers studying data from the radio telescope used by the Canadian Hydrogen Intensity Mapping Experiment (CHIME) found the FRB signals arrived on Earth up to twice an hour for four days before suddenly stopping, only to start up again twelve days later.

Its origin was located within a medium-sized spiral galaxy about 500 million light-years away, making it the closest FRB discovered to date.

The researchers observed its cycle for a total of 409 days and believe that it could be tied to the emitting object being locked in an orbit which lasts 16 days.

However they say that, considering that FRBs are enormously powerful bursts of electromagnetic energy, they could be from a neutron star – although if this was the case the star would be expected to wobble, and not display the same kind of smooth cycle.

The researchers detailed their findings in a pre-print article published on arXiv, ahead of receiving peer review.

In 2017, Professor Avid Loeb, from the Harvard-Smithsonian Centre for Astrophysics in the US, proposed that FRBs could be leakage from planet-sized alien transmitters.

He said that rather than being designed for communication, they would more likely be used to propel giant space ships powered by light sails, which would bounce the beams off a huge reflective sheet to provide forward thrust.

There is currently no evidence supporting the hypothesis that FRBs are connected to alien civilisations.