A group of astronomers led by the University of Warwick have observed a new type of extremely powerful cosmic explosion, leading to a theory that they may be the death song of supergiants.
The cosmic explosions generate strong bursts of gamma rays that can last for several hours. Most gamma-ray bursts, on the other hand, are over in approximately a minute.
The first example of this cosmic phenomenon was discovered by astronomers in 2010, but they could not determine its distance so scientists put forward two competing theories to explain its origin.
The first theory argued that it was down to an asteroid, ripped apart by the gravity of a dense neutron star in our own Milky Way Galaxy. The second theory suggested that it was a supernova in a galaxy approximately 3.5 billion light years away.
The group of astronomers discovered several more examples of these cosmic explosions, revealing that the Christmas Day gamma-ray burst occurred in a galaxy a lot further away than the two competing theories proposed.
Astronomers used data from the Gemini Telescope to draw their conclusions. They calculated that this extremely-long gamma-ray burst was located approximately 7 billion light years away.
Based on information about its location, Andrew Levan at the University of Warwick and his colleagues came up with a new theory to explain how the gamma-ray burst took place.
Their theory argues that this type of burst is brought about by a supergiant, a star that is 20 times more massive than the sun.
They theorize that the gamma-ray burst is long in duration because of the humongous size of the supergiants exploding in a supernova.
Most gamma-ray bursts last a minute or less because they are generated by small, dense stars. The explosion that destroys this new type of gamma-ray burst takes hours to move through the star, which means they last a lot longer.
According to Dr. Levan, these gamma-ray bursts are among the largest explosions in nature, but they are still mostly undiscovered. Only in the past few years have scientists started to get a clearer picture of gamma-ray events.
Co-author Nial Tanvir, a professor at the University of Leicester, says that a newly formed black hole in the center of the star is creating the explosion.
The more common, short-lived gamma-ray bursts are believed to take place when a Wolf-Rayet star in the final phase of its evolution collapses into a black hole at its own core. As matter is pulled into the black hole, some of its energy is focused into a jet of material and blasted out forming gamma-rays in the process.
In the case of gamma-ray bursts in supergiants, the burst has to move through a larger reservoir of material, which is why it lasts longer.
The study’s findings were discussed Tuesday at the GRB 2013 Symposium.