A gamma-ray burst is an extremely luminous event flash of gamma rays that occurs as the result of an explosion, and is thought to be associated with the formation of a black hole.

GRB 090423 and similar events provide a unique means of studying the early universe, as few other objects of that era are bright enough to be seen with today's telescopes.

On April 23, 2009, at 07:55:19 UTC the Swift satellite detected a burst that lasted about 10 seconds and was located in the direction of the constellation Leo.

[4] Attributing this drop off to Lyman alpha absorption by neutral hydrogen in the intergalactic medium, they calculated a redshift of 8.2 for GRB 090423.

Thöne and Paolo D'Avanzo observed the afterglow of GRB 090423 using the Italian TNG 3.6m telescope located in the Canary Islands, Spain.

Derek Fox, who led the observations done by Pennsylvania State University, suggests that the GRB was most likely the result of the explosion of a massive star and its demise, which would probably have signalled the birth of a black hole.

"[17] Nial Tanvir, who was part of the VLT team, suggests that gamma-ray bursts provide a unique tool to study the universe at early times because everything else is too faint to be observed.