X-rays emitted by the explosion glow orange in this image from the Swift Observatory. (Stefan Immler/Swift/NASA)

NASA astronomers think they have figured out the cause of what they had deemed "one of the most puzzling cosmic blasts ever observed."

The massive explosion was likely caused by a star being torn apart after getting too close to a black hole at the centre of a galaxy 3.8 billion light years from Earth, a NASA news release said Thursday.

The explosion, an object dubbed GRB 110328A, has been emitting extremely bright high-energy X-ray and gamma radiation since it was first detected on March 28 — more than a week ago — by a telescope on the Swift Observatory. The observatory is a satellite that orbits the Earth looking for bursts of gamma rays from space.

"We know of objects in our own galaxy that can produce repeated bursts, but they are thousands to millions of times less powerful than the bursts we are seeing. This is truly extraordinary," said Andrew Fruchter, an astronomer at the Space Telescope Science Institute in Baltimore, in a statement.

According to NASA, typical gamma ray bursts usually last only a few hours and are caused by the destruction of a massive star. In this case, the object has grown dimmer and then brighter again a number of times.

Initially, Swift located the explosion in the constellation Draco.

A week later, the more precise Hubble telescope and Chandra X-ray Observatory captured images that showed the object was right at the centre of its galaxy.

Neil Gehrels, lead scientist for the Swift mission, said that means the explosion is "most likely" associated with a massive black hole.

Scientists think the gaseous remains of the star are still falling into a disk around the black hole, causing the formation of a jet of particles moving close to the speed of light, NASA said. That jet appears very bright when viewed head-on by telescopes.