28 April 2009

Spectacular new record set for the Universe’s most distant stellar explosion

A gamma-ray burst, more distant than the farthest known galaxy, has been discovered by a team with researchers from the Niels Bohr Institute at the University of Copenhagen. The gamma-ray burst is light from a star that exploded 13.1 billion years ago. It is the most distant object ever observed in the very early Universe.

"It is a breakthrough in our quest for the very first stars in the Universe," says Johan Fynbo, astrophysicist at the Danish National Research Foundation’s Dark Cosmology Centre at the Niels Bohr Institute. "The discovery tells us that stars had already formed only 600 million after the Big Bang," continues Dr. Fynbo, one of the researchers in the team who found the distance to the burst.

The illustration shows an exploding star with gamma-ray
burst in the early Universe. Artistic rendering: ESO

Gamma-ray bursts are powerful flashes of gamma-rays, lasting from a few seconds to several minutes. They emit vast energies and are among the most violent events in the Universe. The ten-second gamma-ray burst in the constellation Leo was detected by NASA’s Swift satellite on the morning of Thursday 23 April, and was then followed by a series of telescopes on Earth, both the Nordic Optical Telescope, NOT on La Palma and ESO's Very Large Telescope, VLT in Chile.

Observations with the NOT indicated that the gamma-ray burst was very distant; infrared observations with the VLT allowed astronomers to measure the precise distance to the explosion that occurred when the universe was only 600 million years old.

Light in the darkness
The Universe was created 13.7 billion years ago in the Big Bang. The early Universe was a primordial soup of hot gases. The gas cooled and for millions of years the Universe was dark. Nothing existed that emitted light. This period is therefore referred to by astronomers as the "Dark Ages". During this time gravity was gradually compressing the gas ultimately to form the first stars and thus light up the Dark Ages.

"One of the really big questions in astrophysics today is when the first stars were formed, thus ending the Dark Ages. The previous record for the most distant object is a galaxy, which was dated to 740 million after the Big Bang. The new gamma-ray burst is groundbreaking because it is the farthest object ever observed, so now we know for certain that 600 million years after the Big Bang stars and galaxies had formed, "says Professor Jens Hjorth, head of the Dark Cosmology Center.

ESO press release: