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Titanium48
2011-Feb-03, 07:53 AM
In their fate of the universe paper (Reviews of Modern Physics, Vol. 69, No. 2, April 1997), Adams and Laughlin discuss the effects of increasing metallicity star formation, speculating that increasing metallicity will eventually reduce the minimum mass to initiate hydrogen burning to about 4% of the mass of the sun, and that these stars would be so well insulated that water could condense in their atmospheres while fusion slowly proceeded in their cores. Do we know how much additional heavy elements this would require? Is it possible that any of these objects have already formed in locations unusually enriched in heavy elements or by a mechanism that provided heavy element enrichment?

neilzero
2011-Feb-03, 01:44 PM
It appears that metalicity is increasing in the visible portion of the Universe. I suppose in the very far future, some one sol mass star will be less than 50% hydrogen, but why would we suppose that the core would be 50% or even 10% hydrogen in a star that just began main sequence? Can fusion begin in a core that is only 10% hydrogen? would the hydrogen not leave the core and collect near the surface, as the heavier element sank into the core? Neil

CaptainToonces
2011-Feb-03, 02:43 PM
I suspect that such a high-metal star would have sufficient gravitational pressure to fuse its lighter elements, the problem would be that gravity would be TOO strong and would beat out the counter-pressure of the fusion of lighter elements. Nuclei of atomic number greater than or equal to 26 (iron, FE) can't fuse, so the star would likely collapse into a white dwarf early in its life if it had a life of a main-sequence star at all.

baric
2011-Feb-03, 02:58 PM
It appears that metalicity is increasing in the visible portion of the Universe. I suppose in the very far future, some one sol mass star will be less than 50% hydrogen, but why would we suppose that the core would be 50% or even 10% hydrogen in a star that just began main sequence? Can fusion begin in a core that is only 10% hydrogen? would the hydrogen not leave the core and collect near the surface, as the heavier element sank into the core? Neil

Correct. The only fundamental difference between Jupiter and Sol is about one solar mass of hydrogen and helium. :P

A 50/50 metal/gas star would form a solid, electron-degenerate core composed of metals (i.e. a white dwarf) surrounded by an incredibly hot and dense atmosphere of H & He. I'd wager that these conditions, however, would not be sufficient to trigger fusion.

This would essentially be a new type of ultra-heavy brown dwarf.

korjik
2011-Feb-03, 05:01 PM
IIRC, small stars are fully convective. That should keep the star mixed so that the core dosent get choked off of a hydrogen supply. I dont think that it would make all that much difference in the long run tho. It still should look like an ultra-heavy abnormally warm brown dwarf.

Ken G
2011-Feb-03, 08:35 PM
It depends on the mass. If you take a large amount of mass, it could be pure carbon gas and you'd still get a star that is fusing carbon and is an ideal gas. If you don't take enough mass, then the star forms directly into a white dwarf and never reaches carbon fusion temperatures.