A pot of boiling porridge, where instead of grains there are layers of oxygen and silicon, and the fire beneath is about to go out, and the star will collapse in on itself. Until now, astrophysicist cooks have used a simplified recipe: they assumed that bubbles and eddies in the porridge obey one and the same average temperature throughout the depth. But the real porridge turned out to be more capricious.
The team of scientists modeled two types of massive stars (the so-called Wolf–Rayet stars) a few minutes before collapse, using the Aenus-ALCAR code. Instead of a flat picture, they built a volumetric one, accounting for rotation and magnetic fields. In the oxygen layer, the outermost burning one, bubbles moved twice as fast as the old mixing theory prescribed. And in the thin silicon layer, on the contrary, near the very walls of the pot (the layer boundaries), everything quieted down, and mixing there almost disappeared. This directly affects how quickly fuel burns and how homogeneous the material is before the final pop.
These three-dimensional portraits are the first of their kind, ready for calculations of the explosion itself. The difference from one-dimensional recipes means that future supernovae may be born with a different ejecta structure, different composition, and even different brightness. The authors suggest how to incorporate these corrections into fast one-dimensional codes, so as not to recalculate the entire three-dimensional pot from scratch every time.
The thin silicon layer in a star before collapse can be just a few hundred kilometers thick, like the peel of an apple the size of Earth.
In Stanisław Lem's novel 'Solaris', the ocean exhibits unpredictable mixing and structures reminiscent of turbulence in stellar interiors, only on a planetary scale.