The discussion centers around the question of whether 13 billion years is sufficient time for carbon to reach its current abundance in the universe, particularly through processes of stellar nucleosynthesis. Participants explore various aspects of carbon production in stars, including the roles of low-mass and high-mass stars, and the implications for our understanding of cosmic carbon abundance.
Participants generally do not reach a consensus, as there are multiple competing views regarding the contributions of different types of stars to carbon abundance and the implications of recent studies on stellar nucleosynthesis.
There are unresolved questions regarding the exact mechanisms of carbon production in low-mass and high-mass stars, the recycling of stellar material into the ISM, and the impact of different initial mass functions (IMFs) on carbon abundance trends.
phyzguy said:I agree with Vanadium. Clearly yes. Carbon currently represents about 0.4% by weight of the ordinary matter in our galaxy, so the abundance is really not that high. You're seeing a skewed abundance in a place like the Earth, because on a terrestrial planet the main elements (hydrogen and helium) evaporate away.
I think that's just what they meant by the "open question" in the stellar origin of carbon-- not that it's open as to whether stars do it (there's no other game in town), but rather, whether high-mass or low-mass stars do it. It was long thought that low-mass stars retained their carbon, so were not an important source for the ISM, but this is just what recent studies have called into question. I don't know the details about it, but my impression is, the dense winds of AGB stars (low-mass stars becoming red giants for the final time) are now thought to be important carbon sources for the ISM. Judging from the title of that paper, I might speculate that what they are talking about is a process where high-mass stars in the initially "top-heavy" IMF would dominate early carbon formation, but this tends to change the IMF until more low-mass stars are made, which then take over as carbon sources to the IMF.TrickyDicky said:But I have seen a couple of references in the first page after I googled "carbon nucleosynthesis" that point to a carbon open issue for instance with the origin of high carbon abundances in the early universe, as in this article's named "The origin of carbon: Low-mass stars and an evolving, initially top-heavy IMF?" by L. Mattson abstract where they conclude: "The stellar origin of carbon remains an open question, although production in low- and intermediate-mass stars appears to be the simplest explanation of observed carbon abundance trends"
Actually I thought models of stellar nucleosynthesis say that in low mass stars carbon is kept in the core and it doesn't spread out.
Ken G said:I think that's just what they meant by the "open question" in the stellar origin of carbon-- not that it's open as to whether stars do it (there's no other game in town), but rather, whether high-mass or low-mass stars do it. It was long thought that low-mass stars retained their carbon, so were not an important source for the ISM, but this is just what recent studies have called into question.
Ken G said:I don't know myself, but the conclusions that others seem to be reaching is that yes, the high-mass stars by themselves could not have produced the ISM carbon in 13 billion years, they need some help from low-mass stars.
Chronos said:Obviously low mass stars, like the sun, are not major contributors to the interstellar carbon inventory, but, type II supernova are prime suspects. Progenitor stars' atmospheres are carbon rich and, when the core collapses, most of this carbon is dispersed into space.