Huge star burst from the dawn of time

Astronomers have detected a cosmic explosion that is the oldest event ever seen, reports Mark Henderson

10 March 2006

A GIGANTIC star that lived fast and died young in a huge cosmic explosion soon after the dawn of time has been detected by astronomers looking back into the infancy of the universe.

The cataclysmic event took place 12.8 billion years ago, just 900 million years after the Big Bang, and has provided scientists with their first opportunity to study an individual star that formed so far back in time.

On September 4 last year, NASA's Swift satellite picked up a huge burst of gamma-ray radiation coming from the constellation of Pisces. It was identified as the signature of an exploding star with a mass many times greater than the sun's.

Astronomers then watched the 80-second flash using Swift's X-ray telescope and several ground-based telescopes, and published their findings yesterday in the journal Nature.

Gamma-ray bursts are the most violent events in the universe, created when giant stars collapse into black holes at the end of their lives, or by collisions between super-dense neutron stars. They release so much light and energy that they can be seen at vast distances from Earth, over which it is normally impossible to resolve stars or even galaxies.

The newly detected burst, known as GRB 050904, is particularly significant as it is easily the farthest - and thus the oldest - such event ever observed. It took the light generated by the cosmic explosion until now to reach astronomers on Earth.

Never before have scientists been able to see the signature of an individual star - albeit one that has just passed through its death throes - so far away or so long ago.

"This was a massive star that lived fast and died young," said David Burrows, professor of Astronomy at Pennsylvania State University and a member of the study team. "This star was probably quite different from the kind we see today, the type that only could have existed in the early universe. Because the burst was brighter than a billion suns, many telescopes could study it even from such a huge distance."

Enrico Ramirez-Ruiz, of the Institute of Advanced Study at Princeton University, New Jersey, said in a Nature commentary: "Light from the oldest and farthest stellar explosion yet seen was emitted when the universe was a mere infant.

"It provides a close-up view of how and when stars formed ... For the first time, the most distant objects that can be identified are not just galaxies ... but also individual stars."

The event shows that even in the very early life of the universe, huge stars had formed and lived long enough to burn out their fuel supplies and form black holes in great explosions.

While standard theories of the early universe have predicted this, the gamma-ray burst offers the first direct observational evidence that it actually happened.

The research is helping flesh out the story of what happened in the first billion years or so after the Big Bang. Immediately after the Big Bang, the universe was opaque in the "cosmic Dark Ages", which ended between 200 million and 500 million years later. The new work implies the universe then began a furious phase of star formation, producing stars such as the one that triggered GRB 050904, which rapidly burned out.

Daniel Reichart, of the University of North Carolina, who led the scientists, said: "One of the most exciting aspects of this discovery is the brightness of the afterglow -- extrapolating back to a few minutes after the burst, the afterglow must have been exceptionally bright. We are finally starting to see the remnants of some of the oldest objects in the universe."

The Times