NASA/GSFC/DANA BERRY

On September 4, astronomers detected a gamma-ray burst from the farthest reaches of the universe, at a time just 900 million years after its birth. The event represents the most distant such explosion ever recorded.

Signifying the death of massive stars, gamma-ray bursts are some of the universe's most powerful explosions. The September 4th burst, dubbed GRB050904, was first detected by NASA's Swift satellite. Scientists subsequently used a number of telescopes around the world to observe it and determined that it has a redshift of 6.29, which translates to a distance of almost 12.6 billion light-years from Earth. "This is uncharted territory," says team member Daniel Reichart, now at the University of North Carolina at Chapel Hill. "This burst smashes the old distance record by 500 million light-years. We are finally starting to see the remnants of some of the oldest objects in the universe." Reichart and Don Lamb of the University of Chicago predicted in a 2000 paper in the Astrophysical Journal that such faraway gamma-ray bursts could be detected. At the time, astronomers thought that events beyond a redshift of two or three were unlikely.

The results should help researchers better piece together the events of the early universe, particularly the timeline of the earliest stars. "Gamma-ray bursts are uniquely powerful and probably the only way for a very long time to observe the moment of first light--that redshift when the very first stars formed," Lamb remarks. Indeed, GRB050904 was so energetic that within just a few minutes it released 300 times more energy than the sun will release during its entire lifetime.