Exploding Stars at the Edge of the Universe
Gamma-Ray Bursts (GRBs) are bursts of highly energetic gamma rays lasting from less than a second to several minutes – the blink of an eye on cosmological timescales. They are known to occur at huge distances from Earth, towards the limits of the observable Universe. Such bursts occur when a massive star explodes or when two very dense objects merge.
The VLT has observed the afterglow of a Gamma-Ray Burst that is the farthest known ever. With a measured redshift of 6.3, the light from this very remote astronomical source has taken 12.8 billion years to reach us. It is thus seen when the Universe was less than 900 million years old, or less than seven per cent its present age. It must have released 300 times as much energy in a few seconds as our Sun will in its entire lifetime of more than 10 billion years. GRBs are therefore the most powerful explosions in the Universe since the Big Bang.