The fading infrared afterglow of GRB 090423 appears in the centre of this false-colour image taken with the Gemini North Telescope in Hawaii. The burst is the farthest cosmic explosion yet seen, with a distance of over 13 billion light years. ((Gemini Observatory/NSF/AURA, D. Fox and A. Cucchiara (Penn State) and E. Berger (Harvard))

Scientists say a faint burst of radiation discovered last week is the remnant of a massive stellar explosion that took place more than 13 billion years ago, or only about 630 million years after the big bang.

The gamma-ray burst, dubbed GRB 090423, points to what astronomers are calling the most distant object in the universe.

Gamma rays are the highest-energy wavelength of light produced when high-energy particles collide. The large-scale gamma-ray bursts are believed to be produced when massive stars collapse into black holes, releasing jets of gas that react and heat up the gas surrounding the dying star.

Astronomers on Tuesday said they believe the gamma-ray burst discovered is the result of such a stellar explosion.

NASA's Swift satellite first spotted the 10-second-long burst on April 23, but could not see any corresponding visible light to match it. This suggested the burst occurred in an early time of the universe some 13 billion years ago, when dense clouds of hydrogen gas completely absorbed visible light, obscuring our view of a time when scientists believe the first stars and galaxies were born.

Subsequent examinations of the gamma-ray burst were taken from two ground-based telescopes located on Mauna Kea, Hawaii: the United Kingdom Infrared Telescope and the Gemini North telescope.

Redshift signals far-off origin

Astronomers using these telescopes were able to look at the burst's infrared light afterglow to determine the distance of the explosion based on its redshift, or how much the light's wavelength had stretched towards the red end of the spectrum in response to the expansion of the universe.

Just as the sound of a radio from a car moving away from us sounds stretched out, so too does light shift to a longer wavelength as its source moves farther away. Since the universe is expanding, faraway objects are moving away at a faster rate than those closer to us, and so their redshift is correspondingly higher.

The examination of the afterglow confirmed the burst's redshift of 8.2, the highest ever recorded. This corresponds to a distance of 13.035 billion light-years.

"This new gamma-ray burst smashed all the records," said Edo Berger, a professor at Harvard University and one of the scientists that first demonstrated the burst's origin.

"It easily surpassed the most distant galaxies and quasars. In fact, it showed that we can use these spectacular events to pinpoint the first generation of stars and galaxies," he said in a statement.