<p>Have a look at this figure form <a href="https://ui.adsabs.harvard.edu/abs/2004A%26A...425..649H/abstract" rel="nofollow noreferrer">Hirschi, Meynet, Maeder (2004)</a></p>
<p><a href="https://i.sstatic.net/WOHl6.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/WOHl6.png" alt="abundance of elements inside a star" /></a></p>
<p>They are simulating the internal structure of the star and studying its evolution in the pre-supernova phase. This figure refers to a non rotating star of <span class="math-container">$M=20M_\odot$</span> at the end of the Silicon burning stage. It shows the relative abundance of the elements as a function of the lagrangian mass coordinate.</p>
<p>In this figure, the shells are not as clear-cut as in the cartoon in the question you cite, but it is easy to identify a sequence of shells nonetheless.</p>
<p>The sequence I see here is Ni - Si/S - O - O/Ne - O/C - He - H/He</p>
<p>If you go and look at the paper itself, there are many more figures like this one, referring to rotating stars and to different burning stages.</p>

CC BY-SA 4.0
2021-09-03T09:06:14.323Z
2021-09-03T09:06:14.323Z
Prallax
<p>Most textbooks and popular science show highly evolved massive stars with an onion-like structure with layers or shells of different elements fusing. This is clearly approximate (as <a href="https://astronomy.stackexchange.com/questions/44430/do-elements-like-magnesium-and-sulfur-form-a-layer-inside-massive-stars?noredirect=1&amp;lq=1">noted in the comments here</a>), but <em>how</em> <em>approximate</em> is it?</p>
<p>It would seem to me that even in a non-convective environment there would be significant diffusion over stellar timescales that would mix the layers, perhaps into a soft distribution with higher probability of finding heavy elements deeper. But what does actual models and simulations say?</p>

<stellar-evolution><stellar-astrophysics>
How well defined are the elemental shells in evolved stars?
Anders Sandberg
# How well defined are the elemental shells in evolved stars?

(Asked by: username_0 on 2021-09-02)

Most textbooks and popular science show highly evolved massive stars with an onion-like structure with layers or shells of different elements fusing. This is clearly approximate (as [noted in the comments here](https://astronomy.stackexchange.com/questions/44430/do-elements-like-magnesium-and-sulfur-form-a-layer-inside-massive-stars?noredirect=1&lq=1)), but *how* *approximate* is it?

It would seem to me that even in a non-convective environment there would be significant diffusion over stellar timescales that would mix the layers, perhaps into a soft distribution with higher probability of finding heavy elements deeper. But what does actual models and simulations say?

**Tags:** stellar-evolution, stellar-astrophysics

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## 1 answers

### Answer by username_1 on 2021-09-03. Score: 3

Have a look at this figure form [Hirschi, Meynet, Maeder (2004)](https://ui.adsabs.harvard.edu/abs/2004A%26A...425..649H/abstract)

[![abundance of elements inside a star](https://i.sstatic.net/WOHl6.png)](https://i.sstatic.net/WOHl6.png)

They are simulating the internal structure of the star and studying its evolution in the pre-supernova phase. This figure refers to a non rotating star of $M=20M\_\odot$ at the end of the Silicon burning stage. It shows the relative abundance of the elements as a function of the lagrangian mass coordinate.

In this figure, the shells are not as clear-cut as in the cartoon in the question you cite, but it is easy to identify a sequence of shells nonetheless.

The sequence I see here is Ni - Si/S - O - O/Ne - O/C - He - H/He

If you go and look at the paper itself, there are many more figures like this one, referring to rotating stars and to different burning stages.


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