The Sun is a plasma diffuser that sorts atoms by mass
  The Sun is a magnetic plasma diffuser that selectively moves light elements like H and He and the lighter isotopes of each element to its surface. The Sun formed on the collapsed core of a supernova. It consists mostly of iron, oxygen, nickel, silicon and sulfur made near the SN core, like the rocky planets and ordinary meteorites. H ions, generated by emission and decay of neutrons at the core, are accelerated upward by deep magnetic fields, thus acting as a carrier gas that maintains mass separation in the Sun. Neutron emission from the central neutron star triggers a series of reactions that generate solar luminosity, solar neutrinos, solar mass-fractionation, and an outpouring of the neutron decay product, H, in the solar wind. Mass fractionation appears to have operated in the parent star as well, and likely occurs in other stars. 
O. Manuel, S. A. Kamat, M. Mozina