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Abstract

GRB 090423 reveals an exploding star at the epoch of re-ionization

Gamma-ray bursts (GRBs) are extremely luminous gamma-ray flashes produced in Supernova explosions, and detectable up to distances of cosmological interest. Here we report the discovery of GRB 090423, a cosmic explosion occurred when the age of the Universe was only 4% of the current one, corresponding to a redshift z = 8.1. Unexpectedly, this ancient object exhibits properties similar to those of GRBs observed at low/intermediate redshifts, thus suggesting that the mechanisms which produces GRBs in the early and nearby universe are not markedly different. Also it is suggestive of the fact that the massive star which has originated GRB 090423, about 600 milions of years after the Big Bang, shares some of properties which characterize the GRB progenitors exploded bilions of years later. GRB 090423 is the first object discovered into the cosmic transition era, known as dark age, between the time in which the Universe was neutral and opaque, and the time in which it became completely transparent, at the end of the re-ionization era. Its detection provides strong evidence in favor of cosmic GRB evolution in their rate and/or luminosity, suggesting that massive stars form efficiently at those epochs and can play an important role as source responsible for the re-ionization process.

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