We owe our existence to supernovae. Stars fuse all of the heavier elements necessary for life in their cores, which are then expelled out into the Universe when the star dies and explodes into a supernova. Understandably, astronomers are very interested in the process, though there is relatively little known about the arrangement of the elements as the explosion begins. A new three-dimensional computer model has been constructed that utilizes new information to describe how the star behaves in its death throes before it finally blows up.
The model was developed by W. David Arnett and Casey Meakin from the University of Arizona, along with Maxime Vialley from the Max-Planck Institut fur Astrophysik. The team’s paper will be published in the journal AIP Advances, though is is available in an open-source format in arXiv.
Earlier computer models operated on the assumption that elements inside stars were arranged in layers, with the heaviest elements in the center. Those heavier elements affected the gravitational pull of the lighter elements, condensing the star. Neutrinos were created under the pressure and temperature. As the neutrinos left, the star condensed even more. This process continues, until the entire star is ripped apart in an explosion. With such a complex model, the supercomputers of the day weren’t able to process that much information and scientists weren’t able to show multiple events happening at once; they had to be shown as happening in a linear progression.
This new model keeps the heavier elements in the center, but the rest of it is less ordered. Rather than only ejecting neutrinos until it explodes, the star ejects heavier elements from the center in smaller ejection events before the end. The model shows the elements mixing and churning together, which explains why elements don’t come out uniformly in supernova explosions. It is not a smooth, sequential event. It appears that when stars die, they go out kicking and screaming, with several smaller explosions before the final detonation.
The new model utilizes a tremendous amount of new data that scientists have learned over the last several years, making the model more true to observations. This improved data is coupled with the fact that the computers used to design the model are much better and more efficient. Arnett noted: "it would have taken 40 years to run these models on the supercomputers I used in the 1970s. They were feeble compared with my smartphone.”
"Three-dimensional turbulent mixing in a stratified burning oxygen shell which is four pressure scale heights deep. The yellow ashes of sulphur are being dredged up from the underlying orange core. The multi-scale structure of the turbulence is prominent. Entrained material is not particularly well mixed, but has features which trace the large scale advective flows in the convection zone. Also visible are smaller scale features, which are generated as the larger features become unstable, breaking apart to become part of the turbulent cascade. The white lines indicate the boundary of the computational domain." Image credit: Arnett, Meakin and Viallet/AIP Advances