A mysterious short pulse of radio energy picked up by astronomers has been traced to a dwarf galaxy more than three billion light years away.
Dubbed a Fast Radio Burst (FRB), it is one of just 18 known examples of a phenomenon that has puzzled scientists since 2007.
FRBs are highly energetic but very short-lived bursts of radio waves lasting no more than a millisecond.
The first was discovered in 2007 by scientists scouring archived data from Australia’s Parkes radio telescope.
Since then , 17 more FRBs have been identified but only one, spotted in 2012 by astronomers at the Arecibo Observatory in Puerto Rico, has recurred repeatedly.
By studying nine bursts from this FRB over a period of six months, astronomers were able to home in on its exact position in the sky.
FRB 121102 was pinpointed using the Very Large Array (VLA), a multi-antenna radio telescope operated by the US National Science Foundation.
Its location coincided with that of a faint dwarf galaxy far, far away - a distance of more than three billion light years from Earth.
Dr Shriharsh Tendulkar, a member of the team from McGill University in Montreal, Canada, said: "Before we knew the distance to any FRBs, several proposed explanations for their origins said they could be coming from within or near our own Milky Way galaxy.
“We now have ruled out those explanations, at least for this FRB.”
Adding to the mystery, the FRB appeared to be accompanied by a stream of ongoing, persistent weaker radio emissions.
Further high precision observations showed that the two emission sources could not be more than 100 light years apart, said the scientists, whose findings appear in the journals Nature and Astrophysical Journal Letters.
Dr Benito Marcote, from the Joint Institute for VLBI (Very Long Baseline Interferometry) in Dwingeloo, the Netherlands, said: "We think that the bursts and the continuous source are likely to be either the same object or that they are somehow physically associated with each other."
Questions remain
However, what produced the FRB remains unknown.
One likely candidate is a super-dense neutron star - possibly a “magnetar”, a neutron star with a very powerful magnetic field - surrounded by debris from a stellar explosion.
Alternatively, the source could be jets of material shooting out from the rim of a supermassive black hole.
Co-author Dr Shami Chatterjee, from Cornell University in the US, said: "Finding the host galaxy of this FRB, and its distance, is a big step forward, but we still have much more to do before we fully understand what these things are."
The research was presented at the American Astronomical Society's annual meeting in Grapevine, Texas.
PA