<p>A couple of days ago, there was news that &quot;<a href="https://www.sciencemag.org/news/2021/03/some-dead-stars-may-harbor-enough-uranium-set-thermonuclear-bomb" rel="nofollow noreferrer">Some dead stars may harbor enough uranium to set off a thermonuclear bomb</a>&quot;, which is basically a teaser for <em><a href="https://arxiv.org/abs/2103.02122" rel="nofollow noreferrer">Actinide crystallization and fission reactions in cooling white dwarf stars</a></em> where the authors conclude:</p>
<blockquote>
<p>The first solids that form as a white dwarf (WD) starts to crystallize are greatly enriched in
actinides because of their large charges. We estimate that
these first solids could be so enriched in actinides that
they may support a fission chain reaction. This reaction
could ignite carbon burning and lead to the explosion of
an isolated WD in a thermonuclear supernova.</p>
</blockquote>
<p>Going through manuscript, it looks to me that this conclusion is drawn from molecular dynamics simulations  of a cube of up to <span class="math-container">$10^4$</span> ions. <strong>What exactly is the line of argumentation of these microscopic observations from computer simulations are to macroscopic effects in the star?</strong></p>
<p>I understand, that a main question of the research was, whether a certain scenario is actually possible (inside a white dwarf), or literally</p>
<blockquote>
<p>Could uranium, [...], accumulate inside a white dwarf?</p>
</blockquote>
<p>Just to clarify: I am not doubting the conclusion or questioning the method per se, I am just curious whether such an approach is usual for studying stellar evolution. Differently put: Is there a standard theory describing the conditions when the conditions are right for a white dwarf to explode?</p>
<h3>Related</h3>
<ul>
<li><a href="https://astronomy.stackexchange.com/q/42018/37191">How are shockwaves in a star that cause supernova created</a></li>
<li><a href="https://astronomy.stackexchange.com/q/40815/37191">Stellar life cycle flow chart with mass conditions and time scales</a></li>
</ul>

CC BY-SA 4.0
2021-03-22T23:30:05.847Z
The line of argument is that there are no effects that would manifest themselves if they simulated a much larger number of nuclei plus electrons. i.e. There are no long range interactions other than gravity. Your second question is a different one. There are other papers that suggest an ignition temperature for carbon - which is mainly a study of quantum tunnelling probabilities. This paper just suggests that temperature will be exceeded.
ProfRob
CC BY-SA 4.0
2021-03-23T11:04:05.417Z
@ProfRob For the MDS shown in the appendix of the arXiv-manuscript, can you tell which boundary conditions are used for the cube? Do I assume correctly that they use cyclic (toroidal) boundary-conditions or is it actually open boundaries? Which one do you use in general for such kind of problems?
B--rian
<supernova><stellar-evolution><stellar-astrophysics><white-dwarf>
Uranium accumulating inside a White Dwarf?
B--rian
# Uranium accumulating inside a White Dwarf?

(Asked by: username_0 on 2021-03-22)

A couple of days ago, there was news that "[Some dead stars may harbor enough uranium to set off a thermonuclear bomb](https://www.sciencemag.org/news/2021/03/some-dead-stars-may-harbor-enough-uranium-set-thermonuclear-bomb)", which is basically a teaser for *[Actinide crystallization and fission reactions in cooling white dwarf stars](https://arxiv.org/abs/2103.02122)* where the authors conclude:

> The first solids that form as a white dwarf (WD) starts to crystallize are greatly enriched in
> actinides because of their large charges. We estimate that
> these first solids could be so enriched in actinides that
> they may support a fission chain reaction. This reaction
> could ignite carbon burning and lead to the explosion of
> an isolated WD in a thermonuclear supernova.

Going through manuscript, it looks to me that this conclusion is drawn from molecular dynamics simulations of a cube of up to $10^4$ ions. **What exactly is the line of argumentation of these microscopic observations from computer simulations are to macroscopic effects in the star?**

I understand, that a main question of the research was, whether a certain scenario is actually possible (inside a white dwarf), or literally

> Could uranium, [...], accumulate inside a white dwarf?

Just to clarify: I am not doubting the conclusion or questioning the method per se, I am just curious whether such an approach is usual for studying stellar evolution. Differently put: Is there a standard theory describing the conditions when the conditions are right for a white dwarf to explode?

### Related

* [How are shockwaves in a star that cause supernova created](https://astronomy.stackexchange.com/q/42018/37191)
* [Stellar life cycle flow chart with mass conditions and time scales](https://astronomy.stackexchange.com/q/40815/37191)

**Tags:** supernova, stellar-evolution, stellar-astrophysics, white-dwarf
> **Comments:**
> **username_1**: The line of argument is that there are no effects that would manifest themselves if they simulated a much larger number of nuclei plus electrons. i.e. There are no long range interactions other than gravity. Your second question is a different one. There are other papers that suggest an ignition temperature for carbon - which is mainly a study of quantum tunnelling probabilities. This paper just suggests that temperature will be exceeded.  
> **username_0**: @ProfRob For the MDS shown in the appendix of the arXiv-manuscript, can you tell which boundary conditions are used for the cube? Do I assume correctly that they use cyclic (toroidal) boundary-conditions or is it actually open boundaries? Which one do you use in general for such kind of problems?  

---

## 0 answers

