Talk:Stellar core

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Content[edit]

Should this be more generic than solar core ... core of *any* star? Fmadd (talk) 15:40, 13 February 2017 (UTC)[reply]

I changed the "stellar core" redirect into a start-class article so that the more general topic can be covered. For now it just covers the main sequence, but it also needs to discuss pre-ZAMS and evolved giant stars. Praemonitus (talk) 16:22, 21 January 2019 (UTC)[reply]

Red giant section[edit]

I commented one sentence out of this section because it stated that the helium flash was caused by collapse after reaching the Schönberg–Chandrasekhar limit. This isn't true. Schönberg–Chandrasekhar collapse occurs much earlier in the relevant mass range and is key to causing red giant expansion in the first place. This limit is not reached at all in very low mass or high mass stars, and so is responsible for the rapid core collapse and envelope expansion in intermediate-mass stars that makes them transition across the subgiant branch so quickly (and inversely the extended subgiant phase in very-low-mass stars). It also ceases to apply if the core becomes degenerate. The helium flash is caused when the degenerate core increases sufficiently in mass, and hence temperature, to start fusion. Because it is degenerate, fusion begins (almost) simultaneously across the whole core, creating a massive rise in the energy output of the star. This expands the core, shrinks the outer envelope, and (rapidly!) moves the star onto the horizontal branch. This occurs when the core mass is about 0.45 M_☉, regardless of the initial or current mass of the star, or the Schönberg–Chandrasekhar limit, and this is in large part responsible for all red giant branch stars (that experience a helium flash) having the same luminosity just before the helium flash. This may all be moot. Is the section about stellar evolution or stellar cores? Seems that the information about stellar cores is a bit lost in the descriptions of evolution.

Some other thoughts: a pre-main-sequence section? Not really my area, but the structure of stars after the start of fusion but before they reach the ZAMS might be worth describing. AGB stars? Carbon-oxygen cores are interesting. Massive stars? Fusion of heavier elements, core collapse, supernovae, etc. Numbers? I don't think the article mentions the actual mass/size of the stellar cores in the various examples, just the overall star mass. The relative or absolute sizes of the cores would be interesting. Partially convective cores? Plus it might be worth linking or even merging Convective overshoot. Lithopsian (talk) 17:06, 1 July 2019 (UTC)[reply]

Post-main-sequence stellar structure[edit]

The stellar structures for subgiant, red giant branch, horizontal branch, asymptotic giant branch, and supergiant stars are all significantly different. Inert helium core, core helium fusion, inert carbon-oxygen core, hydrogen and/or helium shells, fusion of heavier elements, etc. It seems that separate descriptions are needed for each of these structures. I've added a subgiant section to show the sort of thing I'm thinking of. Obviously it overlaps much of the information in the existing giant star section, but that will be sorted out either by dropping the whole idea or replacing the giant star section with sections on the various evolved star structures. Does this make sense? Does it overlap other articles too much? I've tried to focus on the structure in general, and the core specifically, but its hard to do without explaining what is going on in the life of the star. Lithopsian (talk) 20:42, 1 July 2019 (UTC)[reply]

Thermal and hydrostatic equilibrium[edit]

The minimum temperature required for stellar hydrogen fusion exceeds 10⁷ K (10 MK), while the density at the core of the Sun is over 100 g/cm³.

This sentence doesn't seem to make much sense: the first part is generic while the second part is specific to the Sun.

Perhaps better would be something like:

The minimum temperature required for stellar hydrogen fusion exceeds 10⁷ K (10 MK), while the stellar core density must be over X g/cm³ for equilibrium.

--14.2.29.4 (talk) 21:12, 27 May 2022 (UTC)[reply]

I can see the grammatical improvement, but the physics doesn't make sense. There is no single stellar core density that is required to maintain thermal and hydrostatic equilibrium. For example, the density at the core of a red dwarf is around five times that of the Sun. It might be better to have two sentences, since there are two different things being expressed here. Lithopsian (talk) 10:39, 29 May 2022 (UTC)[reply]

That would make the most sense and be clearer for the reader. GenQuest ^"scribble" 06:30, 1 June 2022 (UTC)[reply]

Hydrogen ignition vs steady state temperature[edit]

This article gives two apparently contradictory figures for the hydrogen-fusion temperature regime. One is that ignition of hydrogen->helium fusion takes place at 10 megakelvin. The other is that red dwarfs, despite being real, hydrogen->helium fusing stars, have a core temperature of less than half that. Other articles agree with both figures, so it's not a mistake, but it does beg for an explanation. -- Dalek955 (talk) 18:36, 24 July 2022 (UTC)[reply]