© NASA/Swift/Stefan ImmlerSwift's X-ray telescope detected blast.
Nasa scientists are trying to solve one of the most puzzling cosmic blasts ever observed.

Stunning images show flaring emission from an explosion which is thought to be the destruction of a massive star in a galaxy 3.8 billion light-years away.

Nasa will use the Hubble Space Telescope, Swift satellite and the Chandra X-ray Observatory to study the blast.

Astronomers say they have never seen anything this bright, long-lasting and variable before.

Usually gamma-ray bursts mark the end of a massive star and emission from these events never lasts more than a few hours.

But radiation from the blast continues to brighten and fade from the location a week after the explosion.

Andrew Fruchter, of the Space Telescope Science Institute in Baltimore, labelled the event as truly extraordinary.

"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 now," he said.

Astronomers believe that the unique blast occurred when a star wandered too close to its galaxy's central black hole.

The gravitational force of a black hole is so strong that it most likely tore the star apart, and the gases released are still streaming towards it.

Nasa believe the information suggests that the spinning black hole formed an out flowing jet of gas and a powerful blast of X- and gamma rays is seen when these jets are pointed towards earth.

© NASA/ESA/A. Fruchter (STScI)Visible galaxy where blast was discovered
Andrew Levan, from the University of Warwick, who led the Chandra observations said "the best explanation at the moment is that we happen to be looking down the barrel of this jet".

Swift's Burst Alert Telescope discovered the source in the constellation Draco, on March 28, when it erupted with the first in a series of X-ray blasts.

On April 4, the telescope pinpointed the position of the explosion at the centre of a distant galaxy near the Swift position.

Astronomers then used Nasa's Chandra X-ray Observatory to make a four-hour-long exposure of the puzzling source. The resulting image locates the object 10 times more precisely than the Swift telescope.

"The fact that the explosion occurred in the centre of a galaxy tells us it is most likely associated with a massive black hole. This solves a key question about the mysterious event," said Neil Gehrels, the lead scientist for Swift at Nasa's Goddard Space Flight Centre.

Astronomers have previously detected stars disrupted by super massive black holes, but none have shown the X-ray brightness and variability seen in this case.

Nasa says the source has brightened more than five times since April 3.

This brightness increase, which is called relativistic beaming, occurs when matter moving close to the speed of light is viewed nearly head on.

Astronomers plan additional Hubble observations to see if the galaxy's core changes brightness.