The ROTSE-III telescope at Siding Spring Observatory	The earth-orbiting satellite Swift. Picture Credit: Spectrum and NASA E/PO, Sonoma State University, Aurore Simonnet

On 2 April 2005 at 00:20:03 Sydney time the gamma-rays from an enormous explosion half-way across the universe hit the earth. The gamma-rays were detected by an earth-orbiting satellite called Swift, which relayed the position to the ground 27 seconds later. Within 6 seconds of receiving the position the UNSW ROTSE-III telescope at Siding Spring Observatory took an image and located a visible counterpart to the gamma-ray object.

This was only the third time that visible emission has been seen during gamma-ray emission. The previous events were in 1999 and 2004. The 2005 event was special since it was the first from a “normal” burst, e.g., one with typical duration and luminosity.

The burst is believed to have resulted from the implosion of a star with from 30 to 100 times the mass of our Sun. The inner core of the star collapses on a timescale of milliseconds at the end of its life, and the surrounding material is converted into energy with an efficiency of 30%. The explosion can release more energy in one second than the Sun does during its entire 9 billion year existence. Any lifeforms in the same galaxy as the explosion would be in considerable danger of extinction.

Fortunately, although there is roughly one gamma-ray burst per day somewhere in the universe, when distributed amongst the 100 billion or so galaxies, we are fairly safe in the Milky Way.

Michael Ashley and Andre Phillips