A sequence of 14 of the 15 detected radio pulses. The streaks are the bursts appearing at different times and different energies

Breakthrough Listen ­– a scientific programme searching for signs of extra-terrestrial life – has detected 15 short but powerful radio pulses emitting from a mysterious source, three billion light years from Earth.

These millisecond-long emissions are called fast radio bursts (FRBs) and are usually attributed to distant galaxies. The source in question – FRB 121102 – intriguingly, is the only one known to repeat. In fact, astronomers have detected more than 150 radio bursts since it was identified.

"Bursts from this source have never been seen at this high a frequency," said Andrew Siemion, director of the Breakthrough Listen programme. This piqued the interest of the Breakthrough team who alerted the astronomical community to the activity on Monday (28 August).

Various theories have been put forward to explain the phenomenon, one being that the signals are coming from a rotating neutron star with an incredibly strong magnetic field. However, some have dared to venture that the bursts from FRB 121102 could conceivably originate from huge transmitters powering an interstellar spacecraft.

"Fast radio bursts are exceedingly bright given their short duration and origin at great distances, and we haven't identified a possible natural source with any confidence," said Avi Loeb of the Harvard-Smithsonian Center for Astrophysics who examined the feasibility of building such a device in a paper published earlier this year. "An artificial origin is worth contemplating and checking."

This is speculative work though and in the search for alien life, all other possibilities must be excluded first. "Science isn't a matter of belief, it's a matter of evidence. Deciding what's likely ahead of time limits the possibilities. It's worth putting ideas out there and letting the data be the judge."

The Breakthrough team observed the latest FRBs over a five-hour period on 26 August using the Green Bank Telescope in West Virginia, accumulating around 400 terabytes of data in the process. This data set was combed for evidence of the short radio bursts.

Whatever is generating the emissions coming from FRB 121102, our solar system was less than 2 billion years-old when they left their source, while life on Earth consisted of just single-celled organisms.

"Whether or not fast radio bursts turn out to be signatures of extra-terrestrial technology, Breakthrough Listen is helping to push the frontiers of a new and rapidly growing area of our understanding of the universe around us," Siemion said.