The Sun - fusion model

[Siggy_G]

While reading further into Michael Gmirkin's recent thunderblog about the current observational inconsistencies with the fusion model of the Sun, I came over this article from 2000 in the Nobel prize (physics) section. It discusses the scientific development that leads to the current theory of how the Sun shines, how the age is calculated and so on. What seems evident, further down the article, is that even mainstream finds some aspects questionable (without making much fuzz about it of course).

http://nobelprize.org/nobel_prizes/phys ... index.html

However, I found this part really amusing:

What was wrong with Kelvin's analysis? An analogy may help. Suppose a friend observed you using your computer and tried to figure out how long the computer had been operating. A plausible estimate might be no more than a few hours, since that is the maximum length of time over which a battery could supply the required amount of power. The flaw in this analysis is the assumption that your computer is necessarily powered by a battery. The estimate of a few hours could be wrong if you computer were operated from an electrical power outlet in the wall. The assumption that a battery supplies the power for your computer is analogous to Lord Kelvin's assumption that gravitational energy powers the sun.

It's funny how close this analogy is to the flaw of the CURRENT model of the Sun and how close it is to a realization... However, a different direction took place, as we know:

The discovery of radioactivity opened up the possibility that nuclear energy might be the origin of solar radiation. (...) What was the connection between Einstein's equation and the energy source of the sun? (...) The idea that nuclear fusion powers stars is one of the cornerstones of modern astronomy and is used routinely by scientists in interpreting observations of stars and galaxies.

Neutrino rates lower than predicted, has some explanations and needs further investigations:

By the middle of the twentieth century, nuclear physicists and astrophysicists could calculate theoretically the rate of nuclear burning in the interiors of stars like the sun. But, just when we thought we had Nature figured out, experiments showed that fewer solar neutrinos were observed at earth than were predicted by the standard theory of how stars shine and how sub-atomic particles behave.

[Jarvamundo]

Clearly they tripped over the cord...

[Jarvamundo]

hahahh.... Just read the article Siggy, quite a good historical wrap up.... but guess who snuck in at the bottom....

5. Perhaps the most imaginative proposal was made by Stephen Hawking, who suggested that the central region of the sun might contain a small black hole and that this could be the reason why the number of neutrinos observed is less than the predicted number.

Even the sun's got a BH now

A special type of BH that selectively sucks in neutrino's only, and doesn't gob gob gobble up your solar fusion fuel... the "Hawking's Neutrino Filter Black Hole"

this guy needs some new moves...

http://www.youtube.com/watch?v=vOxt3cMTDZE

[popster1]

Perhaps Hawking and company should consider this:

"It is tempting, if the only tool you have is a hammer, to treat everything as if it were a nail." - Abraham Maslow

(Their tool, of course, being gravity.)

[MGmirkin]

Then of course there's the question of whether the sun is isodense... If so, bye-bye thermonuclear sun...

~MG

[jjohnson]

But is the sun iso-dense? I puzzled over this (pressure at fluid depth with no underlying mantle) recently at great length, and finally obtained the standard answer from slackerastronomy.org thus: assume that the pressure at the 'surface' is zero, and the fluid material of density 'rho' is incompressible (my question was regarding the water pressure on a hypothetical Earth-sized all-water planet, "Hydra").
Then at any radius r up to surface radius R, the pressure P is expressed as:
P(r) = (2/3) pi G rho^2 (R^2-r^2)

My astronomer helper calculated for me that a sphere of water with a radius of 16.73091 miles has a central pressure of about 1 atmosphere, and a water planet with a radius of 1000km should have a central pressure of 140 MPa, which is a lot of pressure. (-but only 1 atmosphere, 14 psi, 16 miles down? Hmmm! even adding in an overlying atmospheric pressure, that's suspiciously low, at first taste-test!) My calculus textbook says that the force of gravity decreases linearly from the surface acceleration value to zero at the center of a solid, homogenous sphere, which is why I was wondering how to calculate underlying pressure values from a linearly decreasing g loading, using a dV shaped like a square meter at the surface and tapering down to a point at dead center. Well, I'm not very good at calculus so that didn't pan out.

What if the fluid were a cool, non-ionized gas (e.g., hydrogen, H2) which is compressible? That beats me, Pearl! If it compresses, it heats. Heat it enough and it ionizes, and effectively forms a plasma. Then I can't tell you whether it is adiabatic or incompressible under gravity forces any longer or what! Can gravity actually heat hydrogen to the point that it initiates fusion in an ordinary star like ours? It is seeming less and less plausible to me.

By the way, another problem is the ol' sunspots. What is it again that conventional theory says prevents the really hot interior from shining out through these magnetized areas? Can magnetic fields do anything other than polarize outgoing 'light', or do they actually act as filters (like big welders' helmets!) so we can't see that white-hot interior? If there are spectra of just the dark umbra area of some sunspots, it would be interesting to see if they resemble a relatively cool blackbody radiator in the same way as the photospheric radiation of stars follows. If so, it would be reasonable to conclude that the interior actually is cool, and is so revealed no matter where a sunspot appears on the surface.
Jim