2
$\begingroup$

If I remember correctly, the pp chain and (partially) the CNO cycle are the dominating set of reactions in our Sun. On the other hand, the composition of the Sun has many more elements/isotopes than only those involved in the above mentioned reactions:

enter image description here

My question: Can I somewhere find the complete network of reactions 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?"

Improve this question
$\endgroup$
9
  • 2
    $\begingroup$ The other elements are of primordeal origin (thus existed in the gas the Sun formed from) $\endgroup$
    – planetmaker
    Commented Jul 20, 2021 at 13:34
  • 1
    $\begingroup$ 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". $\endgroup$
    – David Hammen
    Commented Jul 20, 2021 at 13:38
  • 3
    $\begingroup$ 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? $\endgroup$
    – David Hammen
    Commented Jul 20, 2021 at 13:48
  • 1
    $\begingroup$ 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)) $\endgroup$
    – planetmaker
    Commented Jul 20, 2021 at 18:02
  • 1
    $\begingroup$ 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. $\endgroup$
    – PM 2Ring
    Commented Jul 21, 2021 at 14:00

1 Answer 1

Reset to default
3
$\begingroup$

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. 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.

Improve this answer
$\endgroup$
5
  • 2
    $\begingroup$ 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). $\endgroup$
    – Peter Erwin
    Commented Jul 20, 2021 at 21:07
  • $\begingroup$ @PeterErwin: NaH (sodium hydride), really? $\endgroup$
    – Incnis Mrsi
    Commented Jul 31, 2021 at 17:19
  • $\begingroup$ @IncnisMrsi OK, not NaH (this paper says it hasn't been detected in any astronomical sources.) $\endgroup$
    – Peter Erwin
    Commented Jul 31, 2021 at 17:42
  • $\begingroup$ On the other hand, I have seen discussions of H$_{2}$ detections in solar spectra... $\endgroup$
    – Peter Erwin
    Commented Jul 31, 2021 at 17:42
  • $\begingroup$ Reference for H$_{2}$ in solar spectrum $\endgroup$
    – Peter Erwin
    Commented Jul 31, 2021 at 19:00

You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .