<p>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 <span class="math-container">$\beta$</span>-decay) and what we know about nuclear physics. </p>

<p>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. </p>

<p>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 <span class="math-container">$\alpha$</span> and <span class="math-container">$\beta$</span> 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. </p>

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

CC BY-SA 4.0
2019-03-17T17:32:13.643Z
"...within a few cm of the neutron star surface." makes me wonder [Do neutron stars have something like a gamma-ray photosphere? Are gamma rays from below it limited more by the nuclei or electrons?](https://astronomy.stackexchange.com/q/30018/7982)
uhoh
CC BY-SA 4.0
2019-03-17T16:35:32.553Z
2019-03-18T07:26:16.667Z
2019-03-18T07:26:16.667Z
ProfRob
<p>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.</p>

<neutron-star><x-ray><spectra><gamma-rays>
Is there evidence of super-heavy elements in the x-ray and gamma-ray spectrums of neutron stars?
Ronald Swager
# Is there evidence of super-heavy elements in the x-ray and gamma-ray spectrums of neutron stars?

(Asked by: username_0 on 2019-03-17)

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.

**Tags:** neutron-star, x-ray, spectra, gamma-rays


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## 1 answers

### Answer by username_1 on 2019-03-17. Score: 7

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.

> **Comments:**
> **username_2**: "...within a few cm of the neutron star surface." makes me wonder [Do neutron stars have something like a gamma-ray photosphere? Are gamma rays from below it limited more by the nuclei or electrons?](https://astronomy.stackexchange.com/q/30018/7982)  

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