Record-Breaking Space Blast Spotted
GRB 080916C's X-ray afterglow appears orange and yellow in this view that merges images from Swift's UltraViolet/Optical and X-ray telescopes.
Credit: NASA/Swift/Stefan Immler

A first sighting for NASA's newest gamma-ray hunter has apparently shattered the record books.

The gamma-ray blast detected by the Fermi (GLAST) Gamma-ray Space Telescope on Sept. 15, 2008 exceeded the power of approximately 9,000 ordinary supernovas, or exploding stars. This assumes that the energy was emitted equally in all directions, although gamma ray bursts usually shoot their energy out in tight jets.

"We were waiting for this one," said Peter Michelson, the principal investigator on Fermi's Large Area Telescope at Stanford University. "Burst emissions at these energies are still poorly understood, and Fermi is giving us the tools to understand them."

Fermi recorded the explosion, designated GRB 080916C, in the constellation Carina. The space observatory's Large Area Telescope and the Gamma-ray Burst Monitor picked up on energies ranging between 3,000 to more than 5 billion times that of visible light in the initial blast.

What happened

Gamma-ray bursts represent the universe's most spectacular light shows anyway. But this burst had the greatest total energy, the fastest motions and the highest-energy initial emissions ever seen.

Astronomers believe that these bursts occur when exotic massive stars run out of nuclear fuel. As a star's core collapses into a black hole, jets of material — powered by processes not yet fully understood — blast outward at nearly the speed of light.

The jets punch through the collapsing star and continue into space, eventually passing through gas veils formerly shed by the star and creating bright afterglows that fade with time.

Such afterglows, which come in various wavelengths of light, provide the opportunity for astronomers to estimate the distance of the gamma-ray burst from Earth. Farther objects have a redder wavelength as the brightness of the explosion fades out among intervening gas clouds.

In the case of the burst detected by Fermi, a ground-based astronomy team at the European Southern Observatory in La Silla, Chile checked out the fading afterglow using a 2.2-meter telescope. With the help of the Gamma-Ray Burst Optical/Near-Infrared Detector, known as GROND, they established that the explosion had taken place 12.2 billion light-years away. That means it occurred 12.2 billion years ago — when the universe was only about 1.5 billion years old — and the light just arrived at Earth.

"Already, this was an exciting burst," said Julie McEnery, a Fermi deputy project scientist at NASA's Goddard Space Flight Center in Maryland. "But with the GROND team's distance, it went from exciting to extraordinary."

And fast!

Astronomers also gauged the slowest possible speeds for material emitting the initial gamma rays. Such gas bullets must have moved at a sizzling 99.9999 percent the speed of light within the jet of the burst — the most extreme recorded to date.

One curious aspect of the burst is a five-second delay separating the highest-energy emissions from the lowest. Such a time lag has been seen clearly in only one earlier burst.

"It may mean that the highest-energy emissions are coming from different parts of the jet or created through a different mechanism," Michelson said. The team's results appeared this week in the online edition of the journal Science.

NASA's Swift satellite coincidentally recorded a different gamma-ray burst just four days after the event picked up by Fermi. The later burst arose from an exploding star 12.8 billion light-years away, making it the farthest such event ever detected.

Editor's Note: This story was corrected to reflect the distance to the object being 12.8 billion light-years, not 12.8 light-years.

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