Image: Gamma-ray burst
NASA/Swift/Stefan Immler
The brightest gamma-ray burst ever seen in X-rays temporarily blinded NASA's Swift's X-ray telescope on June 21, 2010.
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updated 7/14/2010 7:23:13 PM ET 2010-07-14T23:23:13

A violent cosmic explosion has unleashed the brightest blast of X-rays ever detected from distant space, a signal so bright it temporary blinded the NASA space telescope assigned to spot it.

The powerful explosion, called a gamma-ray burst, was detected by NASA's Swift observatory, scientists announced Wednesday. Gamma-ray bursts are narrow beams of intense radiation shot out when stars explode in supernovas. In addition to gamma-ray light, they also produce X-rays and other forms of radiation, including visible light.

This recent event, dubbed GRB 100621A, was particularly powerful.

"This gamma-ray burst is by far the brightest light source ever seen in X-ray wavelengths at cosmological distances," said Penn State University astronomer David Burrows, lead scientist for Swift's X-ray Telescope. (Swift's gamma-ray burst photo)

Unprecedented brightness
The onslaught of light in X-ray wavelengths, which are shorter than visible light wavelengths, quickly overwhelmed the detector when it impacted June 21.

"The burst was so bright when it first erupted that our data-analysis software shut down," said Phil Evans, a postdoctoral research assistant at the University of Leicester in the United Kingdom who wrote parts of Swift's X-ray-analysis software. "So many photons were bombarding the detector each second that it just couldn't count them quickly enough. It was like trying to use a rain gauge and a bucket to measure the flow rate of a tsunami."

Light from this explosion traveled through space for 5 billion years before slamming into Swift, overwhelming its X-ray camera. The observatory, launched in November 2004, was designed specifically to hunt for gamma-ray bursts, though scientists didn't count on a blast quite so strong.

"The intensity of these X-rays was unexpected and unprecedented," said Neil Gehrels, Swift's principal investigator at NASA's Goddard Space Flight Center in Greenbelt, Md.

GRB 100621A was the brightest blast of X-ray light since Swift's X-ray telescope began observing in 2005.

"Just when we were beginning to think that we had seen everything that gamma-ray bursts could throw at us, this burst came along to challenge our assumptions about how powerful their X-ray emissions can be," Gehrels said.

One for the record books
After the shutdown, Swift quickly got back online, and scientists were able to recover the data the observatory acquired during the onslaught. The observations allowed astronomers to learn more about these mysterious explosions, including just how bright they can be.

Swift's measurements showed that the burst emitted 143,000 X-ray photons per second during its short period of greatest brightness. That's more than 140 times brighter than the brightest continuous X-ray source in the sky — a neutron star that releases a steady 10,000 X-ray photons per second.

"When I first saw the strange data from this burst, I knew that I had discovered something extraordinary," Evans said. "It was an indescribable feeling when I realized, at that moment, that I was the only person in the whole universe who knew that this extraordinary event had occurred. Now, after our analysis of the data, we know that this burst is one for the record books."

Gamma-ray bursts focus most of their energy in the short-wavelength, high-frequency range of X-rays and gamma-rays. In fact, they don't stand out at all in optical and ultraviolet wavelengths, emitting only a middling amount of light compared to other objects in the sky.

When a very massive star runs out of fuel and reaches the end of its life, it will collapse into an extremely dense black hole. This event releases an explosion of energy, including some that gets channeled into beams of gamma-ray and X-ray light.

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