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As I understood, low mass stars in their core go through fusion, but only the fusion of hydrogen happens. When it depletes hydrogen, fusion stops as temperature is still not high enough to support fusion of helium and this will never produce other elements such as carbon. The situation is different in high mass stars as they go different stages of fusion.

At least this is how I understood.

I am curious how planets are formed. So after searching, I read that there is gas and dust leftovers that contain carbon, oxygen and some other elements.

Where did the carbon come from? Some say it came from the leftovers of a dying star.

Question: It could NOT have come from the dying high mass star as it would probably form a black hole and that's it. Then we conclude it came from the death of the small star. But how? We know the small stars never go through fusion that produce carbon. So low mass stars could not have brought this. Some mention planetary nebula but I don't get it.

Would appreciate a nice explanation.

EDIT as planetmaker said in the comments, high mass star go through supernova explosion which releases contents (Wikipedia mentions outer layers, but I guess outer layers contain carbon). Does the carbon and other heavy elements get released from the death of small stars as well, and if so, how? Since carbon never is produced in the small star formation and in its fusion.

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  • $\begingroup$ Good question. astronomy.stackexchange.com/questions/40815/… - does that help answer your question, partially or completely? Also: a black hole (only) forms for stars larger than 8 solar masses in a supernova explosion and even then quite some material is released to the surrounding interstellar medium $\endgroup$
    – planetmaker
    Apr 17 at 1:01
  • $\begingroup$ Hey. Thanks for commenting. Sadly no. It will take me quite some time on that link to research where exactly carbon comes from. I was expecting the good/detailed explanation exactly on that(my question). But thanks for pointing that out about black holes. $\endgroup$
    – Giorgi Lagidze
    Apr 17 at 1:52
  • $\begingroup$ So big stars can expel carbon when they die through supernova, but is this the only way we get carbon in a dust that then forms the planet or is there any other way we get carbon in the dust from the small star death and we get back to my question $\endgroup$
    – Giorgi Lagidze
    Apr 17 at 1:58
  • $\begingroup$ Welcome to astronomy SE! If you haven't already, please consider becoming a regularly visiting member of the community. Check the code of conduct for how to act, and take the tour to better understand how the site works. $\endgroup$
    – Deko Revinio
    Apr 18 at 22:42

2 Answers 2

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You need to add some numbers for a definitive answer.

Low mass stars, say less than 0.9 times the mass of the Sun, do not make any contribution to enriching the interstellar medium. That is because all such stars are stil "alive", still on the main sequence, and all their nucleosynthesis products are still inside them.

Stars between about a solar mass and eight solar masses can and do enrich the interstellar medium, including with carbon and a variety of heavy elements. This enrichment occurs near the ends of their lives, particularly during the asymptotic giant branch phase. During this phase, these enormous stars are undergoing helium burning (to carbon) in a shell around an inert carbon and oxygen core (the product of earlier core helium burning on the horizontal branch). The outer envelope is convectively unstable and the convection can reach deeply enough to mix some of the products of helium burning to the surface. From there, it is expelled into the interstellar medium in the form of a massive, radiatively driven, dusty wind. A 5 solar mass AGB star, might lose at least 4 solar masses of material in this way.

Stars higher than eight solar masses also produce carbon and heavier elements in their cores. These stars also go through red giant phases where convection can lift nucleosynthesis products to the surface and they are expelled in a wind. In addition, at the end of their lives, they explode as supernovae, blowing off most of their enriched envelopes. Yes, they may leave behind a black hole or neutron star, but this would usually contain just a small fraction (10-30%) of the original stellar mass.

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    $\begingroup$ Just to point out: the enormous energies involved in the supernovae themselves also contribute to the generation of heavy elements, which would otherwise not be produced through standard stellar core or shell fusion processes. $\endgroup$
    – Izzy
    Apr 17 at 21:40
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All depends on where you put the boundary. According to a Warwick release about a 2020 Nature paper, stars lower than 1.5 solar masses do not contribute to carbon enrichment. But certainly by 2.0 solar masses, they do.

2 solar masses is almost always considered "low mass".

Does the carbon and other heavy elements get releases from the death of small stars as well and if so, how?

Yes, during the AGB phase, material from the core can be brought to the surface and then pushed out on the solar wind.

Jennifer Johnson's table for the origin of elements in the solar system agrees that low mass stars are an important source for carbon.

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