Nature's Brightest Explosion
Astronomers are used to counting the passage of time in millions of years, not seconds – but the moment of March 19, 2008, at precisely 06:12:49 GMT, was a second to remember. Having travelled through intergalactic space for 7.5 billion years after being released by the explosion of a gigantic star in the most distant reaches of the known universe, a brilliant pulse of gamma-ray and X-ray radiation, accompanied by a bright flash of optical light, finally reached Earth.
This flash of light would have been bright enough that under the right conditions, a person staring at the sky with the naked eye would have been able to see this explosion in spite of its distance of 7.5 billion light years – a factor of two thousand times further away than what is normally the record-holder for the most distant object the human eye can see (the galaxy M32, at a comparatively nearby 3 million light years.)
But as far as we know, no person noticed the explosion. Instead, the news was broken by a humble robot – the Swift telescope, a NASA satellite launched in 2004 to study explosions like this one, known to astronomers as "gamma-ray bursts". Within seconds, the instrument's gamma-ray telescope was swamped with signal as thousands of high-energy gamma-rays pelted the detector at once. The robotic telescope, which carries on-board software to quickly re-point itself to quickly stare at the source with its more sensitive X-ray and optical telescopes, rapidly turned and began observations – and was nearly blinded by the accompanying optical flash, which was so bright that the detector was briefly overwhelmed, unable to accurately track the evolution of the event until several minutes later when the explosion began to quickly fade.
Ordinary optical telescopes on the ground, such as the infrared telescope PAIRITEL (images shown at right), met a similar fate – saturated by the initial burst, these telescopes were only able to begin to study the event until several minutes after. Luckily, a few specialized telescopes – small intstruments no larger than a backyard scope, but specially designed to be able to monitor large portions of the sky at once – were small enough to avoid being swamped by the brightness of the event, but still able to track it from its beginning for several minutes, when the larger telescopes took over. These telescopes, including Pi of the Sky, REM/TORTORA, and RAPTOR, allowed scientists to study for the first time exactly what a gamma-ray burst looks like in optical light all the way from beginning to end.
Space can be a violent place – racked by explosions from magnetic storms on neutron stars to supernovae. Yet even among this trigger-happy assortment of rogues, March's gamma-ray burst – catalogued as GRB 080319B – stands out. Since the first recored supernova was discovered in 386 C.E. by Chinese astronomers, it is the brightest (after taking into account the vast distance of this event) explosion ever discovered. In the moments after the explosion, the gamma-ray burst was so bright that it outshone the light from the galaxy it occurred in by a factor of 200,000,000. It took several months for the explosion to fade enough for the galaxy in which it occurred to even be visible again.
The implications of this may be profound. The fact that an event was visible to the naked eye at a distance of 7.5 billion light years implies that if similar explosions occur even further away – at a distance from Earth of 13 billion light years or more, meaning that they occurred in the very earliest phases of the universe, which is 13.7 billion light years old – current and upcoming telescopes would be able to study them in great detail, potentially informing us in great detail about this earliest era in cosmic history.
Page authored by D. Perley (University of California, Berkeley)
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