NASA Satellite Sees Oldest-Ever Gamma-Ray Burst, Long Before Milky Way Existed

photo: GRB 080913 exploded Sept. 13 at a whopping distance of 12.8 billion light-years away in the constellation Eridanus. The box indicates the sky area shown in the Swift image.
Credit: DSS/STScI/AURA



photo: This image merges the view through Swift's UltraViolet and Optical Telescope, which shows bright stars, and its X-ray Telescope, which captures the burst (orange and yellow).
Credit: NASA/Swift/Stefan Immler

Whenever satellites like NASA's Swift sees a gamma-ray burst, it's really a look back in time. Now, scientists have seen one that happened farther back in time than any other seen before.

Gamma-ray bursts or "GRBs" are the most powerful and brightest explosions of energy in our universe. They last only a few milliseconds to several minutes and they outshine all other sources of gamma rays combined. Astronomers now think that most GRBs, those lasting 2 seconds or longer, are associated with the explosive deaths of massive stars. These stars collapse and explode when they run out of nuclear fuel.

Now, NASA's Swift satellite has found the most distant gamma-ray burst ever detected! The blast was named "GRB 080913." The GRB number is actually the date YYMMDD of the burst, with letters used for the first, second, etc. burst of the day. This burst came from an exploding star 12.8 billion light-years away. A light-year is the distance light travels, at a speed 186,000 miles per second, in one year.

"This is the most amazing burst Swift has seen," says the mission’s lead scientist Neil Gehrels at Goddard Space Flight Center in Greenbelt, Md. "It's coming to us from near the edge of the visible universe."

Because light moves at a set speed, looking farther into the universe means looking back in time. GRB 080913's "lookback time" reveals that the burst occurred less than 825 million years after the universe began. Scientists think that the universe is 13.7 billion years old. That means this gamma-ray burst happened 12.8 billion years ago! That's long before our galaxy, called the Milky Way, even existed. Scientists believe the galaxy formed about 10 billion years ago.

The star that created this gamma-ray burst died when the universe was less than one-seventh its present age. "This burst accompanies the death of a star from one of the universe’s early generations," says Patricia Schady of the Mullard Space Science Laboratory at University College London, who is organizing Swift observations of the event.

The star's gamma-rays were registered on NASA's Swift satellite at 1:47 a.m. EDT on Sept. 13. The spacecraft established the burst's location in the constellation Eridanus. The previous record holder was a burst from about 12.1 billion years ago.