So I have been trying to find what stars chemical composition is depending on the stage and I have not found anything beyond the "average star" or our sun. For example out the sun and many others start off at 74% hydrogen,25% helium and 1% other heavy elements and within 5 billion years the chemical composition would be 70% hydrogen, 29% helium and 1% other heavy elements. How could I find the chemical composition of other types of stars such as red supergiants, red giants, blue supergiants, etc; And while doing so I can find out the beginning composition and ending composition with the time that has passed between that shift in the ratio?

  • $\begingroup$ And while doing so I can find out the beginning composition and ending composition with the time that has passed between that shift in the ratio? Is it naive to say the answer to this is the same as you have in your post, the only difference initially is the mass , which determines the time taken to evolve to the stars ending composition, which is very broad in the scope of possible answers, given the wide range of outcomes observed? $\endgroup$
    – user140606
    Feb 10, 2017 at 21:45
  • 3
    $\begingroup$ @Countto10 not quite. The beginning composition is effectively an input parameter for stellar evolution, and does have an effect on how it evolves, and thus its end composition. $\endgroup$ Feb 10, 2017 at 23:10

1 Answer 1


The 'input' parameters for stellar evolution are (*1): mass, binarity, metallicity (a broad term for initial chemical composition), spin, magnetic fields ... etc. Based on these parameters, stars seem to evolve in a very regular way, first burning hydrogen in their core, then i) burning hydrogen in shells outside of a helium core, ii) burning heavier elements in the core (e.g. helium into heavier elements) or iii) stop burning altogether and transition into a remnant state like a white/brown dwarf. Which of these paths they follow depends on their initial configuration (mostly their mass). The type of evolution they undergo then determines their chemical evolution.

Attached is an image showing the chemical structure ('abundance profile') of a massive (15 $M_\odot$) star, right before it explodes as a thermonuclear ('core-collapse') supernova. You can see that the structure is very complex, and involves a large number of species, certainly not just hydrogen and helium. To calculate the structure or composition of stars, one must use numerical simulations---in particular, the standard code is called MESA, which can be downloaded here, and specifications can be found here. MESA was used to produce the solid lines in the attached figure.

enter image description here

*1: I've put these in order of their significance (as we understand it today) in determining how they evolve. i.e. mass is the most important parameter, and so on.

  • $\begingroup$ what is the date range of this? 500 million years? $\endgroup$
    – no name
    Feb 11, 2017 at 1:30
  • $\begingroup$ @noname I'm not sure, it depends on the star's parameters... but probably less, as massive stars evolve fast, perhaps 100 Myr? $\endgroup$ Feb 11, 2017 at 5:07
  • $\begingroup$ Very nice answer. What's up with the sudden changes in $\log X$ at around $m\sim1.72M_{\odot}$? $\endgroup$
    – HDE 226868
    Feb 16, 2017 at 16:47
  • $\begingroup$ @HDE226868 I can't speak to the details, but it's just some transitional radius where some type of burning begins/ends; looks like an Oxygen-Neon burning region... $\endgroup$ Feb 16, 2017 at 19:18

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