Supernova explosions, triggered when the fuel within a star reignites or its core collapses, launch a detonation shock wave that sweeps through a few light years of space from the exploding star in just a few hundred years. (Agencies)
To investigate what may cause these peculiar shapes, an international team led by Oxford University scientists has devised a method of studying supernova explosions in the laboratory instead of observing them in space.
"It may sound surprising that a table-top laboratory experiment that fits inside an average room can be used to study astrophysical objects that are light years across," said Professor Gianluca Gregori of Oxford's Department of Physics.
"In reality, the laws of physics are the same everywhere, and physical processes can be scaled from one to the other in the same way that waves in a bucket are comparable to waves in the ocean. So our experiments can complement observations of events such as the Cassiopeia A supernova explosion," said Gregori, who led the study.
The Cassiopeia A supernova explosion was first spotted about 300 years ago in the Cassiopeia constellation 11,000 light years away, its light has taken this long to reach us.
The optical images of the explosion show irregular 'knotty' features and associated with these are intense radio and X-ray emissions.
Whilst no one is sure what creates these phenomena one possibility is that the blast passes through a region of space that is filled with dense clumps or clouds of gas.
"Our team began by focusing three laser beams onto a carbon rod target, not much thicker than a strand of hair, in a low density gas-filled chamber," said Jena Meinecke an Oxford graduate student, who headed the experiment.
The enormous amount of heat generated more than a few million degrees Celsius by the laser caused the rod to explode creating a blast that expanded out through low density gas.
In the experiments the dense gas clumps or gas clouds that surround an exploding star were simulated by introducing a plastic grid to disturb the shock front.
"The experiment demonstrated that as the blast of the explosion passes through the grid it becomes irregular and turbulent just like the images from Cassiopeia," said Gregori.
"We found that the magnetic field is higher with the grid than without it. Since higher magnetic fields imply a more efficient generation of radio and X-ray photons, this result confirms that the idea that supernova explosions expand into uniformly distributed interstellar material isn't always correct and it is consistent with both observations and numerical models of a shock-wave passing through a 'clumpy' medium," said Gregory.
Supernova explosions, triggered when the fuel within a star reignites or its core collapses, launch a detonation shock wave that sweeps through a few light years of space from the exploding star in just a few hundred years.