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Powerful cosmic explosion helps us step back in time

A mysterious cosmic explosion on May 10 released more energy into the universe in its 100 second burst than the entire Milky Way galaxy has released in more than 30 years.

The explosion was detected as a gigantic burst of gamma rays - high energy radiation - in the sky by NASA's orbiting Compton Gamma Ray Observatory, and by the Italian-Dutch BeppoSAX satellite, triggering a rush by astronomers around the world to focus on the event.

Gamma ray bursts were first discovered 30 years ago by spy satellites looking for clandestine nuclear explosions. Although they occur somewhere in the sky as often as once a day, their cause has been a mystery.

Because they occur at often very great distances, their radiation has been travelling for enormous amounts of time. This makes gamma ray bursts interesting not just in their own right, but as a powerful way to probe the early universe as well.

Among the teams who recorded follow-up observations of the latest burst was one working at the South African Astronomical Observatory, who quickly mobilised optical telescopes to image the visible afterglow accompanying the burst.

Further observations at the European Southern Observatory's Very Large Telescope revealed some fascinating insights. The burst occurred at a distance of about 7,000 million light years, meaning that the rays came from a period of time when the universe was roughly half as old as it is today.

Assuming the emissions were released evenly in all directions from the source, their total energy corresponds to the entire optical energy emitted by the Milky Way in more than 30 years.

But further analysis of the way the light from the afterglow faded is needed to confirm if the radiation was truly spherical. It might in fact be concentrated in a beam pointed towards earth - a feature which would mean less energy was released, and might change theories about the cause of the event.

Among the sources proposed for these explosions are supergiant stars collapsing to black holes, black holes merging with other black holes or with neutron stars - very dense stars at the end of their lives.

But most theories have trouble accounting for explosions with the power of 10,000 million million suns, so it's hoped the enormous amount of information gathered from this recent burst will help shed light on the enigma.