It occurs to me, that between the surface and interior of neutron stars, gravitational pressure might produce super-heavy elements and that signatures of such elements might be detectable in the star's spectrum.


The crusts of neutron stars will contain "super-heavy", neutron-rich nuclei. This is an inevitable consequence of the high density material, the accompanying degenerate electrons (that block $\beta$-decay) and what we know about nuclear physics.

However, the only things that contribute to a neutron star's observable spectrum are materials within a few cm of the neutron star surface. It is expected that this will be made of highly ionised "iron-peak" nuclei (Fe, Co, Mn etc.) and perhaps hydrogen and helium that has been accreted from the interstellar medium.

The "super-heavy elements" won't be present until the densities are much higher than in the surface layers. In a low-density material, these exotic nuclei will simply undergo a series of $\alpha$ and $\beta$ decays or even fission. In high density materials, the electron Fermi energy can exceed the maximum possible decay energy of any beta electrons and stymie the decay process.

e.g. For a surface density of order $10^{9}$ kg/m$^{3}$ (at which point nothing very exotic is created), the electron number density will be about $3\times 10^{35}$ m$^{-3}$. Soft X-rays emitted at $10^{6}$K, will undergo Thomson scattering with a mean free path of $1/n_e\sigma \sim 50$ nm. No (detailed) information about the interior can emerge in such circumstances.

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