US: An unusually long-lasting blast of radiation from a galaxy about 470 million light years away has given astronomers an unprecedented opportunity to view a supernova - a cosmic explosion marking the collapse of a "supermassive star" - from start to finish.
This spectacular cosmic sequence began on February 18th when Nasa's Swift satellite detected a jet of radiation, known as a long-duration gamma ray burst, coming from a galaxy in the constellation Aries.
Within minutes, astronomers throughout the world had trained telescopes on the spot.
Gamma ray bursts are the brightest and most powerful explosions in the universe, but the February 18th explosion was unusual in that it was weaker but much closer to the sun than most detected bursts, which often occur in galaxies billions of light years away. The gamma rays from the burst lasted about 30 minutes, or 100 times longer than a typical burst.
"We've never seen anything like it," said Goddard Space Flight Centre astrophysicist Frank Marshall.
Instead of fading immediately, the optical and ultraviolet light from the burst strengthened for more than two hours and 40 minutes and lingered at its most powerful level for more than a day.
Supernovae and gamma ray bursts are different manifestations of the same event - the collapse and subsequent explosion of a "supermassive star".
Mr Marshall said the energy from a gamma ray burst is hard to quantify because it is expelled in a single beam or "jet," but for this reason it is also regarded as significantly more powerful than the accompanying supernova, which dissipates its energy in all directions. He said optical telescopes should be able to see the supernova for "several weeks