Stellar Explosion Is Most Distant Object Visible to Naked Eye
The extremely luminous afterglow of GRB 080319B was imaged by Swift's X-ray Telescope (left) and Optical/Ultraviolet Telescope (right). This was by far the brightest gamma-ray burst afterglow ever seen.
Credit: NASA/Swift/Stefan Immler, et al.

A powerful stellar explosion that has shattered the record for the most distant object visible to the naked eye was detected by NASA's Swift satellite on Wednesday.

The explosion, known as a gamma-ray burst, also ranks as the most intrinsically bright object in the universe ever observed by humans.

"It's amazing ? we've been waiting for a flash this bright from a gamma-ray burst ever since Swift began observing the sky three years ago, and now we've got one that is so bright that it was visible to the naked eye even though its source is half-way across the universe," said David Burrows of Penn State University, who directs the continuing operation of Swift's X-ray telescope and the analysis of the data it collects.

Gamma-ray bursts are the most luminous explosions in the universe since the Big Bang and occur when massive stars run out of nuclear fuel. The stars' cores collapse to form black holes or neutron stars and release an intense burst of high-energy gamma-rays and jets of energetic particles.

The jets rip through space at nearly the speed of light, heating the surrounding interstellar gas like turbocharged cosmic blowtorches, often generating a bright afterglow.

"These optical flashes from gamma-ray bursts are the most extreme such phenomena that we know of," said Swift science team member Derek Fox, also of Penn State. "If this burst had happened in our galaxy, it would have been shining brighter than the Sun for almost a minute ? sunglasses would definitely be advised."

Penn State astronomer and Swift team member Peter Meszaros said an unusual combination of circumstances may have made the burst's afterglow so exceptionally bright in the visible wavelengths of light.

"When the jet that formed during the explosion of the star slammed into the surrounding gas clouds, shock waves were generated that heated the jet," he explained. "The exceptional brightness of this burst requires the jet to have just the right combination of magnetic fields and velocity, which occurs very rarely."

Astronomers don?t know for sure what made the burst, dubbed GRB 080319B, so bright, but further analysis of the event is under way. The burst could possibly have been more energetic than others, or the burst's energy may have been concentrated in a jet aimed directly at Earth.

The afterglow of GRB 080319B was 2.5 million times more luminous than the most luminous supernova ever recorded, making it the most intrinsically bright object ever recorded.

Astronomers have placed the star in the constellation Bo?tes. They have estimated it to be 7.5 billion light years away from Earth, meaning the explosion took place when the universe was less than half its current age and before Earth formed.

The most distant previous object that could be seen by the naked eye is the galaxy M33, a relatively short 2.9 million light-years from Earth.

The burst was detected by Swift at 2:12 EDT on March 19 and was one of five gamma-ray bursts detected that day, the same day that famed science fiction writer Arthur C. Clarke died.

"Coincidentally, the passing of Arthur C. Clarke seems to have set the universe ablaze with gamma-ray bursts," said Swift science team member Judith Racusin, a Penn State graduate student.

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