GRB 050904 is the most distant gamma ray burst observed as of 2005. It marks the death of a massive star and the birth of a black hole. It comes from an era soon after stars and galaxies first formed, about 500 million to 1 billion years after the Big Bang.

The GRB is 13 billion light years away (in the sense that the light it emitted has taken 13 billion years to traverse the universe to reach us). When this GRB exploded, the age of the universe (according to the most recent estimates) was only 900 million years.

The duration of the burst was 200 seconds, longer than the typical 10 seconds. However, through the effect of time dilation due to the expansion of the universe, the intrinsic duration of the burst was stretched so that the burst appeared longer in the observer's frame of reference.

In papers published in March 2006, the burst was deduced to be caused by a massive star collapsing into a black hole.

This powerful burst was detected September 4. Only one quasar has been discovered at a greater distance. Quasars are super-massive black holes containing the mass of billions of stars. This burst comes from a lone star. Scientists say it is puzzling how a single star could have generated so much energy as to be seen across the entire Universe. The science team has not yet determined the nature of the exploded star. A detailed analysis is forthcoming.

Scientists measure cosmic distances via redshift, the extent to which light is shifted toward the red, or lower energy, part of the electromagnetic spectrum during the light's long journey across the Universe. The greater the distance, the higher the redshift.

The September 4 burst, named GRB 050904, has a redshift of 6.29, which translates to a distance of about 13 billion light-years from Earth. The Universe is thought to be 13.7 billion years old. The previous most distant gamma-ray burst had a redshift of 4.5. The most distant quasar known is at a redshift of 6.4.

This burst was also very long, lasting more than 200 seconds, whereas most bursts last only about 10 seconds. The detection of this burst confirms that massive stars mingled with the oldest quasars. The detection also confirms that even more distant star explosions can be studied through combined observations of Swift and the network of world-class telescopes.

Source: NASA