London, Sept 28 : A radio burst that originated from beyond the Milky Way galaxy has befuddled astronomers.

Initial suspects include the merger of two dense stellar corpses called neutron stars and the complete evaporation of a black hole.

David Narkevic, an undergraduate student at West Virginia University in Morgantown, US, discovered the burst while searching through archived data taken in 2001 by the Parkes radio dish in Australia. He was looking for periodic signals from pulsars – rotating neutron stars – within our galaxy.

But he came upon a short fleeting burst of radio emission that appeared to come from outside the Milky Way.

As electrons in space cause different frequencies of radio waves to arrive at Earth at different times, the scientists used the delay to estimate that the source probably lay about 1.6 billion light years away.

“Our first reaction was, what in the world is this? I didn't expect to see anything out there at all,” said Duncan Lorimer, Narkevic's advisor.

The burst was quite intense and released energy equivalent to that put out by the Sun in one month.

However, it lasted only five milliseconds.

As light can only travel about 1500 kilometres in that time, the researchers believe the object that caused the burst must be no wider than that.

“There aren't too many things in the universe that can do that,” said Lorimer

He said finding more such events in new or archived data could help astronomers make the first ever detection of ripples in spacetime – which should occur when neutron stars merge, according to Einstein's theory of general relativity.

“This is getting speculative, but it could be the last gasp of a black hole, [since] there is supposed to be a little burst of energy associated with that event,” said Lorimer.

“Alternatively, it could be the merger of two neutron stars, which theorists calculate should last only a few milliseconds. Neutron stars also have powerful magnetic fields that would cause charged particles to zoom around them at near-light speeds,” he said.

“That's what radio emission is – coherent electrons spiralling in magnetic fields,” added Dale Frail of the National Radio Astronomy Observatory in Socorro, New Mexico, US.

While mergers are generally thought to cause volleys of high-energy radiation, called short Gamma-Ray Bursts (GRBs), the scientists found no corresponding signals when they searched archived data from gamma-ray observatories operating at the time.

Lorimer said the gamma-ray photons might have travelled out from the merger in a narrower beam than the radio photons, so no GRBs were detected.

“We might have just missed the gamma rays completely because they weren't pointing at us. Hundreds of similar bursts may explode across the sky every day, but they have gone undetected until now because today's radio telescopes focus on only small patches of the sky at once,” he said.

The team is now scouring other archived data to see if any bursts were accidentally caught during observations of other objects.

Though they claim to have already found a few candidate bursts, none are as bright as this event.

The study appears in the journal Science Express, reports New Scientist magazine. (With inputs from ANI)