All change for stellar evolution (Jan 13)

All change for stellar evolution (Jan 13)
http://physicsweb.org/article/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. This
so-called triple-alpha process occurs in the interiors of certain stars
and is important for determining how abundant different elements are in
the universe. The researchers found that at temperatures below about 5 x
10^7 K the rate is significantly higher than previously thought, but
that it is much lower at temperatures above 10^9 K (H Fynbo et al. 2005
Nature 433 136).

Sam Wormley wrote:
The researchers found that at temperatures below about 5 x
10^7 K the rate is significantly higher than previously thought,
but
that it is much lower at temperatures above 10^9 K (H Fynbo et
al. 2005
Nature 433 136).

What do you feel that this will mean for the lifetime of stars by
spectral class? Increase or decrease? - Canopus56

increase.



canopus56 wrote:

Sam Wormley wrote:
The researchers found that at temperatures below about 5 x
10^7 K the rate is significantly higher than previously thought,
but
that it is much lower at temperatures above 10^9 K (H Fynbo et
al. 2005
Nature 433 136).

What do you feel that this will mean for the lifetime of stars by
spectral class? Increase or decrease? - Canopus56

canopus56 wrote:
Sam Wormley wrote:

The researchers found that at temperatures below about 5 x
10^7 K the rate is significantly higher than previously thought, but
that it is much lower at temperatures above 10^9 K (H Fynbo et al. 2005
Nature 433 136).


What do you feel that this will mean for the lifetime of stars by
spectral class? Increase or decrease? - Canopus56


I think the effect on lifetimes will depend on star mass.

Just because some geeks managed to build a hydrogen bomb 60 years ago,
we thought we knew how stars work - LOL! What's that old quote from
Arthur C. Clark?

Sam Wormley wrote:

All change for stellar evolution (Jan 13)
http://physicsweb.org/article/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. This
so-called triple-alpha process occurs in the interiors of certain stars
and is important for determining how abundant different elements are in
the universe. The researchers found that at temperatures below about 5 x
10^7 K the rate is significantly higher than previously thought, but
that it is much lower at temperatures above 10^9 K (H Fynbo et al. 2005
Nature 433 136).

Tim Killian wrote:
Just because some geeks managed to build a hydrogen bomb 60 years ago,
we thought we knew how stars work - LOL!


Evidence shows we know how the Marty, err the Sun, works.

The Proton-Proton Chain
http://csep10.phys.utk.edu/astr162/l...y/ppchain.html
http://www.aip.org/enews/physnews/2003/split/629-2.html
Bahcall et al., Physical Review Letters, 4, April 2003

Competition between the P-P Chain and the CNO Cycle
http://csep10.phys.utk.edu/astr162/l...gy/cno-pp.html
http://www.aip.org/enews/physnews/2003/split/629-2.htm


Neutrino producing reactions adapted [by Lang] from Bahcall (1989). The
termination percentage is a fraction of terminations
of the proton-proton (pp) chain, 4p -- alph + 2e+ + 2Ve, in which each
reaction occurs. Since in essentially all terminations at least one pp neutrino
is produced and in a few terminations one pp and one pep neutrino are created,
the total of pp and pep terminations exceeds 100%

Name Reaction % Termination Neutrino Energy, q
------------------------------------------------------------------------------
pp p + p -- H² + e+ + ve 100 q 0.420 MeV
pep p + e- + p -- H² + ve 0.4 q = 1.442 MeV
hep He³ + p -- He4 + ve 0.00002 q 18.773 MeV
Be7 Be7 + e- -- Li7 + ve 15 q = 0.862 MeV 89.7%
q = 0.384 MeV 10.3%
B8 B8 -- Be7 + e+ + ve 0.02 q 15 MeV


Calculated Solar neutrino fluxes at the Earth's Surface
------------------------------------------------------------------------------
pp 6.0 x 10^10 cm^-2 s^-1
pep 0.014 x 10^10 cm^-2 s^-1
hep 8 x 10^3 cm^-2 s^-1
Be7 0.47 x 10^10 cm^-2 s^-1
B8 5.8 x 10^6 cm^-2 s^-1

Tim Killian wrote:
Just because some geeks managed to build a hydrogen bomb 60 years ago,
we thought we knew how stars work - LOL! What's that old quote from
Arthur C. Clark?

It's Clarke, actually. Lots of old (and not-so-old) quotes from Clarke;
which one are you thinking of?

The change in the model is quantitative, not qualitative. There are
rates at which atomic nuclei interact within the stellar core. From
these rates, the energy production of the star can be predicted, and
thus the lifetimes of the stars. (After all, they only have a limited
amount of fuel at their disposal.)

If the rates have to be modified to account for new observations, that
can be done without scrapping the model entirely, and they result in
different estimates for stellar lifetimes. The basic path of stellar
evolution, however, is essentially the same.

Naturally, there is a difference between the old model and the new
model. Nonetheless, that difference is considerably smaller than the
difference between either and the H-bomb. (The A-bomb from 60 years
ago is a fission bomb, and has little to do with the energy production
of the stars.)

It is an exaggeration to imply that we never knew how stars worked. I
wouldn't say that Newton didn't know how gravity worked, despite the
fact that his theory isn't precisely correct. (Of course, we still
don't know *why* the heck it works, but we have a pretty good handle
on *how* it works.)

Brian Tung
The Astronomy Corner at http://astro.isi.edu/
Unofficial C5+ Home Page at http://astro.isi.edu/c5plus/
The PleiadAtlas Home Page at http://astro.isi.edu/pleiadatlas/
My Own Personal FAQ (SAA) at http://astro.isi.edu/reference/faq.txt

My comment was tongue in cheek, and reflects some personal cynicism with
modern physics and some of the people who practice that flavor of
religious expression.

Thank you for your history lesson on things that go boom, but you are
mistaken -- the idea of a fusion weapon dates back at least sixty years.
To the annoyance of many at the Manhattan Project, in 1944 Edward Teller
began theoretical work for a fusion bomb. And given the security
situation at Los Alamos, the Soviets probably got started on their
version of the H-bomb around that time as well. There was even a report
of a German scientist who experimented with explosively compressing
deuterium gas in silver spheres during W.W.II.

Sakharov and Wheeler both talked informally about processes in stars
that might draw on zero point field energy. But they're both old/dead
now, and the physicists we have today are so much smarter and far better
equipped with super computers and such. Let's not speculate or stray
from the narrow, well-worn path of the Standard Model. Papers must be
published, bills must be paid.

Brian Tung wrote:

Tim Killian wrote:

Just because some geeks managed to build a hydrogen bomb 60 years ago,
we thought we knew how stars work - LOL! What's that old quote from
Arthur C. Clark?


It's Clarke, actually. Lots of old (and not-so-old) quotes from Clarke;
which one are you thinking of?

The change in the model is quantitative, not qualitative. There are
rates at which atomic nuclei interact within the stellar core. From
these rates, the energy production of the star can be predicted, and
thus the lifetimes of the stars. (After all, they only have a limited
amount of fuel at their disposal.)

If the rates have to be modified to account for new observations, that
can be done without scrapping the model entirely, and they result in
different estimates for stellar lifetimes. The basic path of stellar
evolution, however, is essentially the same.

Naturally, there is a difference between the old model and the new
model. Nonetheless, that difference is considerably smaller than the
difference between either and the H-bomb. (The A-bomb from 60 years
ago is a fission bomb, and has little to do with the energy production
of the stars.)

It is an exaggeration to imply that we never knew how stars worked. I
wouldn't say that Newton didn't know how gravity worked, despite the
fact that his theory isn't precisely correct. (Of course, we still
don't know *why* the heck it works, but we have a pretty good handle
on *how* it works.)

Brian Tung
The Astronomy Corner at http://astro.isi.edu/
Unofficial C5+ Home Page at http://astro.isi.edu/c5plus/
The PleiadAtlas Home Page at http://astro.isi.edu/pleiadatlas/
My Own Personal FAQ (SAA) at http://astro.isi.edu/reference/faq.txt

Tim Killian wrote:
My comment was tongue in cheek, and reflects some personal cynicism with
modern physics and some of the people who practice that flavor of
religious expression.

I've seen your cynicism in that regard, yes.

May I ask what you do/did for a living?

Thank you for your history lesson on things that go boom, but you are
mistaken -- the idea of a fusion weapon dates back at least sixty years.

Ahh, yes, of course. But you didn't say "conceived the idea." You
said "managed to build." What we managed to *build* 60 years ago was
the A-bomb, not the H-bomb. I see what you mean now, but you must
admit it wasn't perfectly clear.

That's just a side detail, though. The Sun is not a fusion bomb, not
even writ really really large--at least, not in the sense that a bomb
"blows up."

Sakharov and Wheeler both talked informally about processes in stars
that might draw on zero point field energy. But they're both old/dead
now, and the physicists we have today are so much smarter and far better
equipped with super computers and such. Let's not speculate or stray
from the narrow, well-worn path of the Standard Model. Papers must be
published, bills must be paid.

I think you are mistaken with regard to the Standard Model. Just about
everyone in particle physics recognizes that it must be flawed, for it
predicts zero mass neutrinos, and we know from the Super Kamiokande and
related experiments that at least some neutrinos do have some mass
(albeit in the single eV range). The question lies in how to fix it.

Brian Tung
The Astronomy Corner at http://astro.isi.edu/
Unofficial C5+ Home Page at http://astro.isi.edu/c5plus/
The PleiadAtlas Home Page at http://astro.isi.edu/pleiadatlas/
My Own Personal FAQ (SAA) at http://astro.isi.edu/reference/faq.txt

The question lies in how to fix it.
Neutering jumps to mind.....