Supernova Collapse Explained Using 3-D Model
The disintegration process of a supernova has always generated interest among astronomers. Now scientists have developed a powerful three-dimensional model, which shows the violent explosions that leads to the death of a supernova, causing bursts of luminous radiations that can briefly outshine galaxies and release materials that over millions of years make life on Earth possible.
The model, developed by W. David Arnett, Regents Professor of Astrophysics at the University of Arizona in association with Casey Meakin and Nathan Smith at Arizona, and Maxime Viallet of the Max-Planck Institut fur Astrophysik, is the first to represent a supernova's collapse in 3-D. Published in the journal AIP Advances, the model shows how the mixing of heavy and light elements inside a star causes expansion, contraction, and finally a violent collapse of the star.
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Arnett's obsession with building supernova explosion models began with the supernova of 1987 called 1987A. It exploded in a nearby dwarf galaxy and was visible to the naked eye. Astronomers at that time, were puzzled by the star since the explosion remnants seemed to mix with the material that was ejected before the explosion and this process could not be explained in existing models.
To understand the supernova, scientists analyzed the light and radioactivity from its remnants and then created models of physical processes that behaved similar to a supernova. In these models, a star was shown as a series of concentric circles with heavier elements like iron and silicon in the center and lighter elements like carbon, helium, and oxygen towards the surface. The heavier elements exert a gravitational pull causing the core of the star to contract thereby increasing the temperature and pressure. This causes the star to collapse and release its binding energy in the form of neutrinos. But as the neutrinos are released, the lighter elements get pulled towards the core and this causes the star to collapse further.
"It heats up and burns faster, making more neutrinos and speeding up the process until you have a runaway situation," Arnett said.
These models are large and complex and in order to run them on supercomputers, researchers had to develop them in one or two dimensions, thus restricting these models. These models show a supernova's disintegration as a smooth process. But Arnett's 3-D model shows a different process in which a violent star core releases material before the final explosion, similar to how rapidly heating a pot causes water to boil over the edge.
"We still have the concentric circles, with the heaviest elements in the middle and the lightest elements on top, but it is as if someone put a paddle in there and mixed it around. As we approach the explosion, we get flows that mix the materials together, causing the star to flop around and spit out material until we get an explosion," Arnett said. "That's what we see in supernova remnants," he added, referring to the ring of heavy and light elements that form nebulas around stars that went supernova. "We see those ejections of star material, and how they mix with material expelled from the star during its final explosion. Other models cannot explain this."
Arnett's model is more sophisticated as it uses better data and faster computers. In order to make accurate models the scientists need better data on supernovas, which are very rare. But observatories such as the Katzman Automatic Imaging Telescope (KAIT) and Palomar Supernova Factory are dedicated to searching for supernovas, with the use of state-of-the-art telescopes. The data that they have collected gives a better insight into how stars die.
"Instead of going gently into that dark night, it is fighting. It is sputtering and spitting off material. This can take a year or two. There are small precursor events, several peaks, and then the big explosion.
"Perhaps we need a more sophisticated notion of what an explosion is to explain what we are seeing," said Arnett.
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