Interesting results concerning stellar evolution

[Sven]

http://physicsweb.org/articles/news/9/1/8
Models of how quickly stars evolve may have to be modified after astrophysicists found that the rate at which three helium nuclei transform into carbon-12 is very different from earlier estimates.
Fynbo and co-workers calculated that, for temperatures below about 5 x 107 K, the triple-alpha reaction rate was significantly higher than the standard rate [...] This means that the stars could have evolved twice as quickly.
At temperatures above 109 K, on the other hand, the reaction rate was much lower than NACRE's. This could be important for models of nucleosynthesis -- the process that forges all heavier elements -- in supernovae.
Just wait and see Creationists jump on this:
"See, now evilutionists say that stars are much younger! This proves that Genesis is true!"

On a more serious note (and sparked by recent discussions): I wonder if these results also impact our theories of galaxy formation.

[Shadowy Man]

I wonder if these results also impact our theories of galaxy formation.

Certainly possible, but it seems that it could have significant impact on studies of chemical evolution of galaxies. If stars are evolving at faster rates, they would be enriching the interstellar medium with metals on shorter timescales.

[Schneibster]

Certainly possible, but it seems that it could have significant impact on studies of chemical evolution of galaxies. If stars are evolving at faster rates, they would be enriching the interstellar medium with metals on shorter timescales.Hmmm, didn't I comment on a thread about the metallicity of NGC 7603 yesterday? What do you know, here is the explanation.

[Sven]

Hmmm, didn't I comment on a thread about the metallicity of NGC 7603 yesterday? What do you know, here is the explanation.
Yeah, that's why I wrote "sparked by recent discussions" in the OP :)

[beausoleil]

They haven't shown that stars are half the age we thought, or anything like that. They are talking about the effects of their work on models of the evolution of the earliest stars.

Stars slightly bigger than our sun fuse hydrogen nuclei using 12C as a catalyst (the CNO cycle ). The very first stars formed with no 12C (none formed in the big bang), so even if they were big enough for the CNO cycle they didn't fuse hydrogen this way at first. In effect, the way they worked was different from the way massive stars work today.

However, a v.small amount of 12C was produced in them by the triple-alpha process as they were burning hydrogen. This work shows that the time it took for them to produce enough 12C to switch on the CNO cycle was about half what had been modelled.

That's what I understand from their paper, anyway.

iirc, the lifetimes of the first stars were estimated to be ~1-10 Ma because they were so massive (lack of metals also affects the collapse process of clouds by removing a cooling mechanism, so huge stars are expected). So they now reach the CNO stage twice as fast, but still run through subsequent evolution and death. The effect on the age of the galaxy and on stars that start with enough 12C is slight.

[Sven]

The effect on the age of the galaxy and on stars that start with enough 12C is slight.
Thanks for your input! :thumbs:

[beausoleil]

You're welcome - but I should add I'm just putting my interpretation.

Also, part of their work that isn't mentioned is that the rate of 12C production at higher temperatures is lower than previously thought, which will have a significant impact on our understanding of AGB stars and supernovae.