A gamma-ray burst from the edge of the visible universe has been spotted by NASA's Swift observing satellite. Astronomers said on Monday it's the most distant explosion ever.

This powerful burst, detected on September 4, marks the death of a massive star and the birth of a black hole. It comes from an era soon after stars and galaxies first formed, about 500 million to 1 billion years after the Big Bang.

The fact that the burst occurred at 13 billion light years away means what the Swift telescope spotted actually happened 13 billion years ago, while the Universe is thought to be 13.7 billion years old according to the Big Bang theory, the researchers explained.

They measure cosmic distances by redshift, the extent of light shifting toward the red, or lower energy, part of the electromagnetic spectrum during the light's long journey across the Universe.

The greater the distance, the higher the redshift. The September 4 burst, named GRB 050904, has a redshift of 6.29, equal to a distance of about 13 billion light-years from the Earth. The previous most distant gamma-ray burst had a redshift of 4.5. The most distant quasar known is at a redshift of 6.4.

The Swift satellite detected the burst first and notified scientists of its location. Then scientists used the Southern Observatory for Astrophysical Research telescope in Chile to discover the burst afterglow, and nail down the distance. A Japanese team confirmed the distance and fine-tuned the redshift measurement to 6.29 later.

"We designed Swift to look for faint bursts coming from the edge of the Universe," said Neil Gehrels, Swift principal investigator.

"Now we've got one and it's fascinating. For the first time we can learn about individual stars from near the beginning of time. There are surely many more out there."

This burst comes from a lone star, astronomers said while beingpuzzled how a single star could have generated so much energy as to be seen across the entire Universe. The team has not yet determined the nature of the exploded star.

This burst was also very long, lasting more than 200 seconds, whereas most bursts last only about 10 seconds. The detection of this burst confirms that massive stars mingled with the oldest quasars, and that even more distant star explosions can be studied through combined observations of Swift and the network of telescopes.

One of the best ways to study the earliest stars is watching for their explosions, mission scientists said. The Swift satellite can pinpoint the location of the explosions with its gamma ray detector, and telescopes can study the composition of the debris to understand where and when these stars formed and what they weremade of.

"This is uncharted territory," said Daniel Reichart at University of North Carolina, Chapel Hill, who led the distance measurement.

"This burst smashes the old distance record by 500 million light-years. We are finally starting to see the remnants of some of the oldest objects in the Universe."