Astronomers searching for signals from alien civilisations have detected 15 powerful, repeated radio pulses coming from a dwarf galaxy 3 billion light years away from Earth.

The source of the mysterious signals, known as fast radio bursts, is unknown. Some have proposed they could be emanating from black holes or rotating neutron stars with extremely strong magnetic fields. A more speculative possibility is that they are beacons from extraterrestrial spacecraft.

The signals were picked up by the Breakthrough Listen project, a $100m (£77m) initiative to find signs of intelligent life in the universe set up by Professor Stephen Hawking and Russian internet billionaire Yuri Milner.

About two dozen fast radio bursts have been detected previously. Because they last only a few milliseconds and radio telescopes can only monitor a small area of the sky at any given time, only one of these sources has been observed to repeat.

The source, known as FRB 121102, was discovered in 2012 and resides in a dwarf galaxy about 3bn light years from Earth.

Now 15 more signals have been observed from the same source and at a higher frequency than the previous signals – although what this signifies about the source of these mysterious events is not yet clear.

“As well as confirming that the source is in a newly active state, the high resolution of the data obtained by the Listen instrument will allow measurement of the properties of these mysterious bursts at a higher precision than ever possible before,” said Breakthrough Listen postdoctoral researcher Vishal Gajjar, who discovered the increased activity.

Andrew Siemion, director of the Berkeley SETI Research Center and of the Breakthrough Listen programme, said: “Whether or not fast radio bursts turn out to be signatures of extraterrestrial technology, Breakthrough Listen is helping to push the frontiers of a new and rapidly growing area of our understanding of the universe around us.”

The findings were reported on the Astronomer’s Telegram website.