A cosmic explosion unlike any observed and recorded before has astronomers the world over reviewing theories of how the largest bangs in the Universe (since the Big One) actually occur.

The strange Gamma Ray Burst (GRB) occurred on June 14 in a galaxy two billion light years away, and although it had some features in common with typical GRBs, it was also quite different. 

Professor Brian Schmidt, Dr Bruce Peterson and postdoctoral student, Karen Lewis, from the Research School of Astronomy and Astrophysics at ANU, tracked the Gamma Ray Burst at Siding Spring Observatory near Coonabarabran for the first few hours after it was recorded by NASA’s Swift Space Mission on June 14. They were part of an US led team to study the GRB and publish a paper in upcoming edition of the journal Nature.

“Gamma Ray Bursts are the most powerful of cosmic explosions observed in the Universe and usually they come in two types. Typically, a GRB is either short – less than two seconds – or long. This burst was clearly in the long category lasting 102 seconds,” Professor Schmidt said.

“Before this explosion, conventional wisdom was that short GRBs were the result of two dead stars – called neutron stars - merging to form a black hole. Long bursts were the result of the death of a star more than 40 times more massive sun forming a black hole. These long bursts have always been associated with a stellar explosion – or supernova – which typically last tens of days and are billions of times brighter than the sun.

“But with this GRB no matter how hard we looked, from how many angles and how many times, there was no supernova. Furthermore, Gemini Observatory and Hubble Space Telescope observations revealed that the explosion occurred in a galaxy which contained almost no massive stars. So the object is puzzling. It’s a long way outside the box of what we have seen and predicted before – and has thrown a spanner into our theories of how these objects explode,” Professor Schmidt said.
 
The ANU astronomers were part of an international team to publish a paper in a special edition of the international science journal Nature on GRB 060614 (referring to the date it was detected, 14 June 2006).
“It also showed that the job of understanding Gamma Ray Bursts was still a way off,” Dr Avishay Gal-Yam of the California Institute of Technology, said. “Perhaps this is the first example of a new kind of GRBs, coming neither from massive stars that explode as supernovae, or from merging binary compact objects, but from something totally new.”

Although it was the first recorded observation of a ‘hybrid’ gamma ray burst, the astronomers believe it is probably not an uncommon phenomenon. This explosion was not quite two billion light years away and in the scheme of the cosmos that is nearby. “There is place for many more of these objects to hide in the distant Universe,” Professor Schmidt said.

More information: http://www.astro.caltech.edu/~avishay/grb060614.html

ANU Media Office: Simon Couper 02 6125 4171 / 0416 249 241