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 8.2.
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 8.1.
These studies imply that massive stars were being produced and were dying as -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 -ray bursts 10 billion years later.
"The burst also pinpoints the location of its host galaxy," noted N. R. Tanvir and colleagues.