<blockquote>
<p>What I am actually after is to answer more scientifically the children's question: &quot;What happens if I throw something in the Sun?&quot; and my answer was always &quot;It burns.&quot; but I am now wondering about the &quot;How does it burn?&quot;</p>
</blockquote>
<p>It doesn't burn. What happens when an object such as an asteroid or comet impacts the Sun is in a sense the opposite of burning. The 5578 kelvins (5505 °C) temperature of the surface of the Sun is so high that it causes any chemical compound to undergo <a href="https://en.wikipedia.org/wiki/Thermal_decomposition" rel="nofollow noreferrer">thermal decomposition</a>. For example, a water molecule decomposes into two hydrogen and one oxygen atoms. No chemical compound can withstand such high temperatures.</p>
<p>So it's not burning that causes the spectral lines. Those spectral lines are dark areas in what otherwise appears to be close to black body radiation from an object at 5778 kelvins.</p>
<p>What causes them to occur is that elements absorb radiation at specific frequencies. This absorption of a photon raises an electron from one orbital state to another. The electron will eventually relax to its lower energy state, resulting in a photon of the same frequency being emitted, but in a random direction. The photons emitted toward the Sun -- we don't see them. What we see is holes in the spectrum at those absorption frequencies.</p>

CC BY-SA 4.0
2021-07-20T21:07:32.933Z
Nitpick: there *are* some simple molecules in the Sun's photosphere, which show up as absorption lines (e.g., CN, CH, NaH, OH, ...). And I believe water has even been detected in sunspots (which are of course lower temperature).
Peter Erwin
CC BY-SA 4.0
2021-07-31T17:19:49.930Z
@PeterErwin: NaH (sodium hydride), really?
Incnis Mrsi
CC BY-SA 4.0
2021-07-31T17:42:14.493Z
@IncnisMrsi OK, not NaH ([this paper](https://ui.adsabs.harvard.edu/abs/2015MNRAS.451..634R/abstract) says it hasn't been detected in any astronomical sources.)
Peter Erwin
CC BY-SA 4.0
2021-07-31T17:42:54.117Z
On the other hand, I have seen discussions of H$_{2}$ detections in solar spectra...
Peter Erwin
CC BY-SA 4.0
2021-07-31T19:00:04.650Z
[Reference for H$_{2}$ in solar spectrum](https://astronomy.stackexchange.com/questions/45005/is-there-molecular-hydrogen-in-the-suns-atmosphere-if-so-how-much-and-how-wa/45008#45008)
Peter Erwin
CC BY-SA 4.0
2021-07-20T14:26:26.333Z
2021-07-20T14:26:26.333Z
David Hammen
<p>If I remember correctly, the <a href="https://en.wikipedia.org/wiki/Proton%E2%80%93proton_chain" rel="nofollow noreferrer">pp chain</a> and (partially) the <a href="https://en.wikipedia.org/wiki/CNO_cycle" rel="nofollow noreferrer">CNO cycle</a> are the dominating set of reactions in our Sun. On the other hand, the <a href="http://hyperphysics.phy-astr.gsu.edu/hbase/Tables/suncomp.html" rel="nofollow noreferrer">composition of the Sun</a> has many more elements/isotopes than only those involved in the above mentioned reactions:</p>
<p><a href="https://i.sstatic.net/JJkSt.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/JJkSt.png" alt="enter image description here" /></a></p>
<p>My question: <strong>Can I somewhere find the complete <a href="https://en.wikipedia.org/wiki/Chemical_reaction_network_theory" rel="nofollow noreferrer">network of reactions</a> taking place in the Sun?</strong></p>
<p><strong>Edit:</strong> What I am actually after is to answer more scientifically the children's question: &quot;What happens if I throw something in the Sun?&quot; and my answer was always &quot;It burns.&quot; but I am now wondering about the &quot;How does it burn?&quot;</p>

CC BY-SA 4.0
2021-07-20T13:34:27.090Z
The other elements are of primordeal origin (thus existed in the gas the Sun formed from)
planetmaker
CC BY-SA 4.0
2021-07-20T13:36:19.640Z
@planetmaker Yeah, I know that all heavier elements are primordeal, and must have been produced in hotter stars of previous generations. But do the other element react with each other or burn in some way? The fact that we have spectral lines does mean that they are burning at some rate, or does it?
B--rian
CC BY-SA 4.0
2021-07-20T13:38:39.950Z
The pp chain and CNO cycle are nuclear reactions, and they are the only nuclear reactions that take place in the Sun. Those other elements in the Sun were formed in other stars, before the solar system formed. It appears your are asking us to write what would amount to be a book on the "complete network of (chemical) reactions taking place in the Sun".
David Hammen
CC BY-SA 4.0
2021-07-20T13:40:11.457Z
@DavidHammen I guess my question is more a spectroscopic one, as I tried to highlight in my previous comment.
B--rian
CC BY-SA 4.0
2021-07-20T13:46:46.323Z
@planetmaker I added a bit of background info to my question.
B--rian
CC BY-SA 4.0
2021-07-20T13:48:41.500Z
It's not burning that causes the spectral lines. You might want to rewrite your question so that you are not asking us to write a book. Are you asking what causes those spectral lines to appear, or what happens when an object falls into the Sun?
David Hammen
CC BY-SA 4.0
2021-07-20T13:58:07.243Z
@DavidHammen: Actually both. Maybe I should make it two questions then. I will do that in my next free time slot.
B--rian
CC BY-SA 4.0
2021-07-20T18:02:18.337Z
It looks to me like at least two separate questions: a) origin of the spectral lines in the Sun's spectrum. b) genesis of the elementary composition of the Sun (and maybe its temporal evolution) c) nuclear reactions inside the Sun's core and d) chemical reactions in the Sun's photopshere and corona (which is faintly related to (a))
planetmaker
CC BY-SA 4.0
2021-07-21T14:00:39.447Z
As Wikipedia says, the CNO cycle in the Sun is currently responsible for 1.7% of the He production, but that will rise as the core temperature rises. There *are* other nuclear processes in the Sun, but they're pretty marginal, eg uranium decay and [cosmic ray spallation](https://en.wikipedia.org/wiki/Cosmic_ray_spallation).
PM 2Ring
<the-sun><spectra><nucleosynthesis>
Spectral lines of the Sun?
B--rian
# Spectral lines of the Sun?

(Asked by: username_0 on 2021-07-20)

If I remember correctly, the [pp chain](https://en.wikipedia.org/wiki/Proton%E2%80%93proton_chain) and (partially) the [CNO cycle](https://en.wikipedia.org/wiki/CNO_cycle) are the dominating set of reactions in our Sun. On the other hand, the [composition of the Sun](http://hyperphysics.phy-astr.gsu.edu/hbase/Tables/suncomp.html) has many more elements/isotopes than only those involved in the above mentioned reactions:

[![enter image description here](https://i.sstatic.net/JJkSt.png)](https://i.sstatic.net/JJkSt.png)

My question: **Can I somewhere find the complete [network of reactions](https://en.wikipedia.org/wiki/Chemical_reaction_network_theory) taking place in the Sun?**

**Edit:** What I am actually after is to answer more scientifically the children's question: "What happens if I throw something in the Sun?" and my answer was always "It burns." but I am now wondering about the "How does it burn?"

**Tags:** the-sun, spectra, nucleosynthesis
> **Comments:**
> **username_1**: The other elements are of primordeal origin (thus existed in the gas the Sun formed from)  
> **username_0**: @planetmaker Yeah, I know that all heavier elements are primordeal, and must have been produced in hotter stars of previous generations. But do the other element react with each other or burn in some way? The fact that we have spectral lines does mean that they are burning at some rate, or does it?  
> **username_2**: The pp chain and CNO cycle are nuclear reactions, and they are the only nuclear reactions that take place in the Sun. Those other elements in the Sun were formed in other stars, before the solar system formed. It appears your are asking us to write what would amount to be a book on the "complete network of (chemical) reactions taking place in the Sun".  
> **username_0**: @DavidHammen I guess my question is more a spectroscopic one, as I tried to highlight in my previous comment.  
> **username_0**: @planetmaker I added a bit of background info to my question.  
> **username_2**: It's not burning that causes the spectral lines. You might want to rewrite your question so that you are not asking us to write a book. Are you asking what causes those spectral lines to appear, or what happens when an object falls into the Sun?  
> **username_0**: @DavidHammen: Actually both. Maybe I should make it two questions then. I will do that in my next free time slot.  
> **username_1**: It looks to me like at least two separate questions: a) origin of the spectral lines in the Sun's spectrum. b) genesis of the elementary composition of the Sun (and maybe its temporal evolution) c) nuclear reactions inside the Sun's core and d) chemical reactions in the Sun's photopshere and corona (which is faintly related to (a))  
> **username_3**: As Wikipedia says, the CNO cycle in the Sun is currently responsible for 1.7% of the He production, but that will rise as the core temperature rises. There *are* other nuclear processes in the Sun, but they're pretty marginal, eg uranium decay and [cosmic ray spallation](https://en.wikipedia.org/wiki/Cosmic_ray_spallation).  

---

## 1 answers

### Answer by username_2 on 2021-07-20. Score: 3 | Accepted answer

> What I am actually after is to answer more scientifically the children's question: "What happens if I throw something in the Sun?" and my answer was always "It burns." but I am now wondering about the "How does it burn?"

It doesn't burn. What happens when an object such as an asteroid or comet impacts the Sun is in a sense the opposite of burning. The 5578 kelvins (5505 °C) temperature of the surface of the Sun is so high that it causes any chemical compound to undergo [thermal decomposition](https://en.wikipedia.org/wiki/Thermal_decomposition). For example, a water molecule decomposes into two hydrogen and one oxygen atoms. No chemical compound can withstand such high temperatures.

So it's not burning that causes the spectral lines. Those spectral lines are dark areas in what otherwise appears to be close to black body radiation from an object at 5778 kelvins.

What causes them to occur is that elements absorb radiation at specific frequencies. This absorption of a photon raises an electron from one orbital state to another. The electron will eventually relax to its lower energy state, resulting in a photon of the same frequency being emitted, but in a random direction. The photons emitted toward the Sun -- we don't see them. What we see is holes in the spectrum at those absorption frequencies.

> **Comments:**
> **username_4**: Nitpick: there *are* some simple molecules in the Sun's photosphere, which show up as absorption lines (e.g., CN, CH, NaH, OH, ...). And I believe water has even been detected in sunspots (which are of course lower temperature).  
> **username_5**: @PeterErwin: NaH (sodium hydride), really?  
> **username_4**: @IncnisMrsi OK, not NaH ([this paper](https://ui.adsabs.harvard.edu/abs/2015MNRAS.451..634R/abstract) says it hasn't been detected in any astronomical sources.)  
> **username_4**: On the other hand, I have seen discussions of H$_{2}$ detections in solar spectra...  
> **username_4**: [Reference for H$_{2}$ in solar spectrum](https://astronomy.stackexchange.com/questions/45005/is-there-molecular-hydrogen-in-the-suns-atmosphere-if-so-how-much-and-how-wa/45008#45008)  

---

