Light from a star that exploded 13 billion years ago has reached Earth, setting a new record for the most distant astronomical object yet observed. The characteristics of the explosion, known as a gamma-ray burst, show that massive stars were already forming only 630 million years after the Big Bang.
The detection of the gamma-ray burst, named GRB 090423, is reported in two papers in this week's Nature. Two teams of astronomers, led respectively by Nial Tanvir and Ruben Salvaterra, each measured the redshift of the object at about 8.2, meaning that the burst occurred when the Universe was less than 5% of its current age. The previous record-holder was a galaxy at redshift 6.96, corresponding to an age 150 million years younger than GRB 090423.
Beyond the mere breaking of a record, the age of the newly detected object opens a window into a cosmological era that has not previously been accessible to observation. The cosmic "Dark Ages" are thought to have ended about 800-900 million years after the Big Bang, when light from stars and galaxies re-ionized the previously neutral gas pervading the Universe. As more gamma-ray bursts are detected from these early times, it should be possible to trace the progress of this re-ionization, leading to the intergalactic medium we see today.