As a huge star nears its death, it begins to shoot out superfast jets of particles. Credit: © Nicolle Rager Fuller/NSF

Using a satellite and a global network of telescopes, astronomers have glimpsed the most distant cosmic explosion ever seen.

The explosion, known as a gamma-ray burst, probably came from a star that died when the Universe was in its infancy. The light from the burst could give researchers insight into the first stars and the ways in which the cosmos has changed over time.

Gamma-ray bursts occur, most astronomers believe, during the death throes of giant stars. When stars die, they sometimes explode violently in a process known as a supernova. During the course of the explosion, a star can eject a plume of particles at near light speeds.

This event is pointing the way to the absolute first stars that ever formed. George Ricker , Massachusetts Institute of Technology

These particles release an enormous amount of energy in the form of superfast gamma rays. The gamma-ray bursts are so intense that they can outshine entire galaxies, says Donald Lamb, an astrophysicist at the University of Chicago in Illinois.

The challenge for astronomers is that most gamma-ray bursts last only a few seconds or minutes before fading away. To help locate them quickly, NASA launched the aptly named Swift satellite, a space-based gamma-ray telescope that locates a burst within seconds and e-mails its coordinates to nearly 1,000 astronomers around the world. The researchers race to direct their telescopes to the point in the sky where the burst was first spotted, and study its afterglow, which can last for hours or days.

Time travel

The light from this latest burst, which was spotted on 4 September, came from a star that exploded when the Universe was a mere 900 million years old. That's about one-fifteenth of its present age, says Nial Tanvir, an astronomer at the University of Hertfordshire, UK, who is using a telescope in Cerro Pachon, Chile and is among the first to study the afterglow of the burst. Astronomers watched the burst fade for several days, using telescopes in Hawaii, Chile, Colorado and other locations around the world.

The burst provided a rare glimpse back through space and time, says Tanvir. The light from the burst travelled through the clouds of dust that lie between the dying star and Earth, illuminating a narrow beam of the otherwise dark Universe. "It's like being in the headlights of a car," he explains. A Japanese group in Hawaii has gathered data that could help to show exactly what the early Universe looked like.

The burst is also important because it happened at a time when the Universe was hugely different from its present state, says George Ricker, an astronomer at the Massachusetts Institute of Technology in Cambridge, Massachusetts. If we can spot an explosion this old, he says, we might eventually be able to peer even further back in time. "This event is pointing the way to the absolute first stars that ever formed, before there were galaxies at all," he says.