Scientists see blast from past -- 13 billion years ago

File image shows a time exposure of the night sky above the Swiss mountain resort of Grindelwald January 10, 2008.

WASHINGTON (Reuters) - Astronomers have seen the furthest back in time ever, measuring light from a star that exploded 13 billion years ago, just after the dawn of the universe.

They traced a gamma-ray burst called GRB 090423 to see the light from the massive star that died 630 million years after the Big Bang that brought the universe into being, they reported in the journal Nature on Wednesday.

Two separate teams measured the redshift of the object at about 8.2. Redshift is the distortion of light as it travels across space and time and is often likened to the sound of a train rising and falling as it approaches and passes the listener.

This extreme redshift -- the highest ever recorded -- shows the burst occurred when the universe was less than 5 percent of its current age, Nial Tanvir of Britain's University of Leicester and colleagues reported.

"The redshift measured for GRB 090423 means that the burst occurred at a time when the universe was about nine times smaller than it is today -- putting the timing of the event at about 630 million years after the Big Bang," Bing Zhang of the University of Nevada wrote in a commentary.

"Gamma ray bursts are the most violent explosions in the universe," he added.

"They are believed to be associated with the formation of stellar-sized black holes or rapidly rotating, highly magnetized neutron stars during cataclysmic events such as the collapse of a massive star or the coalescence of two compact stellar objects."

In this case, the star's death long ago was bright enough to outshine even galaxies and will help scientists understand what happened in the early days of the universe.