Two letters to Nature today burst into data about a gamma-ray burst, GRB 090423. The first is A big gamma-ray burst at a redshift of z approximately 8.2 by N. R. Tanvir et al. The second is GRB 090423 at a redshift of z approximately 8.1 by R. Salvaterra et al.
First detected by NASA Swift satellite on April 23, 2009 at 3:55 a.m. EDT, GRB 090423 was observed on the ground within minutes of its discovery. Gemini Observatory in Hawaii attempted an observation in optical (visible) light and when the detection was negative, used the Near-infrared Imager/Spectrograph to make the observation in several infrared wavelengths. These images were combined to make the color image released today. (See below)

In addition to the Gemini observations, the object was detected by the United Kingdom Infrared Telescope (UKIRT, also on Mauna Kea) early on the same evening as the Gemini imaging. Tanvir et al. used the UKIRT from about 20 minutes after the burst and arrive at z approximately 8.2.

“I have been chasing gamma-ray bursts for a decade, trying to find such a spectacular event,” said Edo Berger, a leader in the scientific team that made the discovery in Gemini
and professor at Harvard Smithsonian Center for Astrophysics. “We now have the first direct proof that the young universe was teeming with exploding stars and newly-born black holes only a few hundred million years after the Big Bang.”  


Above is the distribution of redshifts and corresponding age of the Universe for gamma-ray bursts detected by NASA Swift satellite. GRB 090423 at a redshift of z=8.2 broke the previous record for gamma-ray bursts, also exceeding the highest redshift galaxy and quasar discovered to date, and became the most distant known object in the Universe. GRB 090423 exploded on the scene when the Universe was only about 630 million years old, and its light has been travelling to us for over 13 billion years.

The fading infrared afterglow of GRB 090423 appears above in the center of this false-color image taken with the Gemini North Telescope in Hawaii. The burst is the farthest cosmic explosion ever seen.

The second letter by Salvaterra et al. reports an initial detection with the Swift satellite on 23 April 2009, and a redshift determination with the Telescopio Nazionale Galileo on La Palma 14 hours after the burst, obtaining z approximately 8.1.

These studies imply that massive stars were being produced and were dying as gamma-ray bursts as early as about 600 million years after the Big Bang. Those stars were not the first generation, however. We know from their properties that they are very similar to other stars producing gamma-ray bursts 10 billion years later.

"The burst also pinpoints the location of its host galaxy," noted N. R. Tanvir and colleagues.