I'd be beyond the limits of my understanding of supercritical fluids if I tried to answer to that. It probably isn't as simple as I'm making it sound. The basic idea that I'm using is that once compressed into the closest packed arrangement, yet above the critical temperature, all of it becomes fluid, and then the heavier atoms sink to the bottom. But that is surely naive. In the Earth's crust, below the Moho the matter is compacted to the point that the crystal lattices break down, and the matter loses its rigidity. We can see plenty of evidence of plasticity in the folded layers of rock that subsequently found their way to the surface. We can also see crystals that don't normally form at the surface. For example, graphite can get compressed into diamonds. If there is a mix of elements present, chemicals can form, which required extreme pressure. So what's the closest packed arrangement when a variety of elements are present? Is it all of one kind of element at one level, and then all of another at the next level? Or are there smaller elements nestled in the voids left by the closest packed arrangement of larger elements? In other words, imagine an orthogonal arrangement of iron atoms, in perfectly aligned rows & columns. Perhaps the Coulomb force between iron ions won't let the rows or columns get compacted anymore. But on the diagonal, there will be some empty space that could get filled in with hydrogen or helium. So once the iron gets compacted, there won't be any force to expel the hydrogen or helium from the mix, and it will just stay there.johnm33 wrote:I have another probably stupid question for Charles, looking at the image on your page 7909 of the suns layers, is it possible that the inner layers are suffused with hydrogen ions packed into a matrix of the other elements?
What kind of "chemicals" might be present at such extreme pressures? What would the properties of those "chemicals" be (e.g., wave transmission speeds, thermal and electrical conductivities, etc.)? Would any of those crystal lattices persist if brought to the surface? All very interesting questions. Perhaps somebody knows the answers, but we don't have the lab data to confirm any of it, and QM certainly won't help -- only a physical model can predict physical properties.
But I think that the extreme temperatures probably present inside the Sun will keep stirring up the mix, which will let gravity have more of an effect than it would at lower temperatures.