It seems to me that the alternative models for the sun, introduced now in several threads, all suffer from a considerable lack of appreciation for the strong foundations of the standard model for the sun. So, I start this thread with two ideas in mind.

1) I will start by giving a brief historical account of how the current standard model came to be, and I will finish it up with a reference to my own webpage on the sun.

2) The continuing discussion should avoid any direct discussion of alternative models, and concentrate on the sole topic of the viability of the standard model. What's wrong with it? Does it fail some empirical test? Is it incompatible with observation? Does it violate the laws of physics? Why is the standard model supposed to be so bad? Why do we need an alternative anyway?

Historical introduction to the standard model

The first edition of Encyclopedia Britannica (1771) describes the sun as an "immense globe of fire". The description in Thomas Squire's A Popular Grammar of the Elements of Astronomy (London, 1820, the oldest astronomy book in my library) is no different. Indeed, prior to the mid 1800's, astronomy books pretty much avoid the stars, and spend lots of pages talking about the solar system. They simply didn't know what stars were.

A major breakthrough in understanding the sun comes in the late 1800's, in two books by J. Norman Lockyer: Studies in Spectrum Analysis (1878) and Elements of Astronomy (1886). The science of spectroscopy had been discovered decades before (see history of spectroscopy for details), but these books deliver the first discussions of a complete study of spectroscopy applied to the sun. In Neither book does Lockyer make any definitive statement as to the elements that make up the sun, but he does list the number of spectral lines observed, and they are all metals, iron having the most spectral lines visible. It was from this time that the then standard model of the sun held that it was made mostly of heavy elements, as were the planets. After all, at the time, there was no reason to believe that the constituent elements of the sun were remarkably different from the planets, even though its temperature was known to be much higher.

It is also worth notice that in his 1886 book, Lockyer speculated on whether or not the sun could be inhabited. He did realize that no living creature could withstand the high temperature of the photosphere. But it was unknown at that time, whether sunspots provided a view of a solid surface below the hot photosphere. Lockyer speculates that something could live on such a surface, if it could avoid the heat.

Simon Newcomb's 1906 book, The Stars - A Study of the Universe, is the oldest astronomy book I have that concentrates on stars, rather then planets. But even here, Newcomb says nothing specific about the chemical constituents of the stars, other than to briefly relate the spectroscopic studies of Lockyear, and others. At the turn of the 19th/20th centuries, it was still not known what the stars were really made of, but it was known that heavy metals were most evident in the spectra.

The first "real" book on stellar physics is Eddington's Internal Constitution of the Stars (1926). It was followed by Charles G Abbot's less technical, but more specific book, The Sun (1929). By this time Eddington had demonstrated that the sun (and stars in general) could not be made mostly of heavy elements (i.e., metals), because the opacity of these elements lead to internal pressures that do not permit them to have the observed brightness & radius (by proxy with the sun, the only star close enough to get a radius for). Not everyone went along with Eddington, and Abbot relates that Jeans argued that the core of the sun must be made of heavier elements, specifically uranium and heavier. Eddington & Jeans were on opposing sides in the argument over the chemical constituents of the sun.

In the ensuing years, Eddingtons arguments won out. Perhaps the single most significant piece of research was that done by the American astronomer Henry Norris Russell: On the Composition of the Sun's Atmosphere, Astrophysical Journal 70: 11-82, July, 1929. Russell made it quite clear that the atmosphere of the sun, the part we could see, was mostly hydrogen, despite all of the metal lines seen by early spectroscopists. Other important papers followed, which served only to strengthen the move away froma "mostly metals" sun (i.e., Notes on the constitution of the stars, H.N. Russell, Monthly Notices of the Royal Astronomical Society 91: 951-966, June 1931; The opacity of stellar matter and the hydrogen content of the stars, Bengt Stromgren, Zeitschrift für Astrophysik 4: 118-152, 1932; On the Helium and Hydrogen Content of the Interior of the Stars, Bengt Stromgren, Astrophysical Journal 87: 520-534, June 1938, to cite just a few). It had become increasingly clear that the sun was made mostly of hydrogen & helium.

While the chemical constituency of the sun was under discussion, so too was its source of energy, which was perhaps even more mysterious. Nevertheless, by the time Eddington had written Internal Constitution of the Stars, it was evident that some kind of nuclear process was responsible, though nuclear fusion was as yet unknown. When Chandrasekhar wrote his book, An Introduction to the Study of Stellar Structure, in 1938 (published in 1939), it was well understood that (a) the sun ws made mostly of hydrogen, and (b) some nuclear process was responsible for energy generation in the core of the sun.

The problem of energy generation by fusion was finally solved by Hans Bethe, who eventually was awarded a Nobel Prize, primarily for this discovery (The Formation of Deuterons by Proton Combination, H.A. Bethe & C.L. Critchfield, Physical Review 54(4): 248–254, 15 August 1938; Energy Production in Stars, H.A. Bethe, Physical Review 55(1): 103, 1 January 1939; Energy Production in Stars, H.A. Bethe, Physical Review 55(5): 434–456, 1 March 1939).

So, while Eddington, Russell, Stromgren & others had settled the chemical constituency of the sun, Bethe & Critchfield had also settled its source of energy. This was the status of solar study, when WWII started. This basic model of the sun, a mostly hydrogen gas spheroid has remaind intact since then, though in the ensuing 65 years or so, a great deal of additional advancement has been made in understanding the solar interior, and especially the chromosphere, corona & solar wind, which were still not well understood at that time.

Here I will break off the narrative, and refer the reader to my webpage: Solar Fusion & Neutrinos. On that page I give a fairly up to date description of the fusion processes, and a discussion of the solar neutrino problem. I have also included copious references to webpages, and books for further reading (some of which are suitable for the non mathematically inclined reader). Those books & webpages will bring you up to date on the details of current thinking in solar astrophysics. But I wanted to establish a historical context here, that is not on the webpage.

I think it is noteworthy, especially in light of models suggested both by Mozina & Manuel, that there was a time when the standard solar model was in fact, a mostly iron sun. But that model was abandoned as astronomers & physicists learned more & more about the sun. They discovered that such models simply could not survive scrutiny, and there has been no good reason, yet, to go back to the old models.

So we are left with the eminal question: What's wrong with the standard solar model?

Whaaaaat? No pretty pictures? How can you describe something whitout images? And where are the photos showing those neutrinos originating from inside the sun? You've provided only a bunch of equations and graphs, nothing consistent!
Ok, ok, I'll shut up...

Actually I wanted to say that I've found interesting your brief history about how has evolved our knowledge about stars; also, IMO, this thread doesn't belong to ATM. Maybe it should be moved in a general science section...

The problem with moving it to General Science is that the people who most need to read this would never look there for it.

Interesting post Tim. I picked up a book on Solar astronomy this weekend and it said pretty much of the same about the history of solar models, in particular that there is not much before the 19th century. No idea where Michael Mozina got his "Galileo gas model" from. (I notice that he no longer uses that phrase here.)

__________________
Microsoft is over if you want it.

The bar has been lowered for the promotion of ATM ideas; the bar for the acceptance of ATM ideas must remain high.

I have a question for you Tim. Helioseismology studies have suggested a rigid-like rotating core between ~0.2Rs to 0.7Rs with the [assumed] differencial rotation of the radiative layer above that. Can you speculate on what that rigidly rotating "body" might be comprised of?

Is it possible that the solar magnetic field is generated in the same basic method as Earth's--that is to say, is it related to the different rotational speeds between the core and radiation zone combined with the convectiion of that radiative zone?

Do you think there is an equivalent to the D" layer seen at the mantle/core boundary of Earth?

__________________
All civilizations become either spacefaring or extinct.~ Carl Sagan ~

Humanity must rise above the Earth, to the top of the atmosphere and beyond, for only then will we fully understand the world in which we live.~Socrates, 500 B.C. ~

Let every man judge according to his own standards, by what he has himself read, not by what others tell him. ~Albert Einstein~

For some time there is a controversy about the Neon abundance, this article explains the problem.

Abstract:
This is corroborated in this article

Could you explain what these findings mean for the solar model? Personally I don't really trust numbers derived from "solar interior models", but even so any model should be consistent with observations.

Cheers.

I am not sure what you mean by this comment VL. Observations suggest that the alteration of the neon/oxygen abundances in the solar atmosphere as suggested by Bachall et al (2005) and Anita & Basu (2005) is not the answer for why there is a slight discrepancy between the Standard Solar Model and observations of the sun.

The idea that neon may have been to culprit arose because of studies of active cool stars by Drake & Tesla (2005). As this thesis did not match the observations, there is another culprit that must be identified and tested.

Pretty good science, IMHO.

__________________
All civilizations become either spacefaring or extinct.~ Carl Sagan ~

Humanity must rise above the Earth, to the top of the atmosphere and beyond, for only then will we fully understand the world in which we live.~Socrates, 500 B.C. ~

Let every man judge according to his own standards, by what he has himself read, not by what others tell him. ~Albert Einstein~

Thanks Tim,

I was of the opinion that a fairly major change was required in the standard convection model after we learned the H/He ratio on Jupiter is the same as the solar ratio. Footnote?

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jwj

It's ok not to know.

It's the convective layer that is differentially rotating, everything outwards from ~0.7 Rs. The part of the sun that appears to be "rigidly" rotating is the radiative zone, the part that lies between ~0.2 and ~0.7 Rs. The reason for this is not known indetail, but I suspect the answer is rotational shear working on the convective zone. Since the rotation is axial, but the convection is radial, you can readily see that the convective zone can shear into horizontal motion that depends on the latitude. See, for instance, Rotation of the solar interior, a chapter from the book Dynamic Sun, or perhaps Helioseismology, which appeared in Reviews of Modern Physics. Or look up The Internal Rotation of the Sun, which appeared in the 2003 issue of Annual Reviews of Astronomy and Astrophysics.

I think, as do most, that the solar magnetic field is driven by motions in the outer, convective zone of the sun, especially near the tachocline, which is the boundary between the lower radiative zone, and the upper convective zone. Large-Scale Dynamics of the Convection Zone and Tachocline is in Living Reviews of Solar Physics, and should be visible without a subscription. Or see the Solar Dynamo page from Marshall Space Flight Center.

I doubt it. The core/mantle boundary in Earth is a sharp phase transition, where the outer core is liquid, and the mantle is "solid" (it's actually more "plastic", you might think of it as an extremely viscous liquid). There shoul not be a phases transition like that, so deep inside the sun.

Did I question the science?
You say a "slight discrepancy", is that your interpretation or is it from the articles I linked to? Because these articles are discussing a "controversy" and it needs to be resolved. If you look at the abundances and the error bars, you will notice they are not overlapping, so it's a real problem at least in the minds of the authors of the 2 articles I linked to. There is another article on the astro-ph database today telling us the same thing.

So, what's up?

Cheers.

Just wanted to add this Asplund et al. article that confirms the discrepancy between the Standard Solar Model (SSM) and observation of Neon abundances.

So Tim, I ask again, what's up?

I also want to ask what this Lefebvre et al. article means in terms of the SSM.

Abstract:
To me this suggests that the 11 year cycle of the Sun is centered only "skin deep" into the solar surface, in other words, there would have to be either another "transition layer" very close to the solar surface, or generation of the magnetic fields is not as you say around the 0.7 Rsun.
This is only a few thousand kilometers deep, it ties in very well with earlier observations that show that there is a region around sunspots that is detectable by helioseismology and is described as "superficial".

Cheers.

Isn't it fairly obvious what's up? There is a discrepancy between the interpretive implications of the helioseismic observations, and the interpretive implications of the spectral data. Both are complicated affairs, and the discrepency remains to be explained.

Now, I already know how you will respond, because you always respond in the same, predictable vein: Why not assume that the standard model is wrong, and find a better one? But I have a better question: Why assume that the standard model is wrong?

Scientific models which do not sport some discrepency with some observations are actually rather rare, and highly prized when found. So the mere existence of a discrepancy is, by itself, not a big deal. The existence of a lot of discrepancies would be a bigger deal, and maybe a genuine BIG deal, if there are enough of them. But what is really important is the fundamental aspect of the discrepancy, because that is what leads one to have confidence that the discrepancy is of such magnitude as to suggest that the model is entirely wrong, in which case we would look for a better one.

So, does this discrepancy threaten the standard model? it might, one day, but certainly does not now. That's because both the spectroscopic & helioseismic analyses are quite complicated, and there is room for differences due to small mistakes, or systematic bias buried in the data reduction (which is quite different between the two), or some other unforeseen cause.

Now, Bachall et al. had suggested one possibility, that the neon abundance by itself, could be off enough to cause the problem. It turns out that this is most likely not the case. But it is remarkable that such a suggestion would even appear to be right. That diddling the abundance of just one element could, in principle, eliminate the discrepancy altogether suggests that the discrepancy is not a fundamental problem, and will go away (or at least shrink in magnitude), once the kinks in the details of analysis are found & conquered.

So I might ask you the same question now. What's up? Is the standad model really ready for the trash heap now, just because (maybe) the neon abundance is a problem? I wouldn't bet any real money on that.

It suggests to me what it explicitly says, namely that the radius of the sun is not constant, that the sun pulsates slightly on an 11 year cycle. It has long been known that the radius of the sun is not constant, and does vary with time, so that is of little consequence. Fixing the variability to the magnetic field cycle is actually quite encouraging to the standard model, since one would not be surprised by such a coincidence of effects.

Since around 0.995 solar radii, the variation switches from in-phase to anti-phase, it could suggest a "skin deep" effect, but not necessarily that the magnetic field is actually generated so close to the surface. It could also suggest that the field, generated near the tachocline, is subject to turbulent shear, and reconfigures itself (a poloidal -> toroidal transition, perhaps?) near the surface. That would be consistent with the generation of sunspots due to shearing of the field.

Now this observation is one that is predcited by the standard model of sunspot cooling, and is an encouraging observation. The magnetic field of the sunspot blocks convection of heat into the sunspot material, forcing convection to flow around the sunspot, heating the area around it. This is pointed out at the end of the "superficial" page you posted.

What's an eminal question?

Ok, so doesn't a discrepancy show that something is wrong with the standard solar model?

The authors of all three papers think it is a big deal , maybe you don't so could you explain why the Neon discrepancy is no big deal, maybe some links?

So what is the evidence that a deep layer is responsible for the magnetic fields? It seems to me that the skin deep explanation works for the entire solar surface, not just for sunspots. If you say "but not necessarily that the magnetic field is actually generated so close to the surface" what is the evidence against such a claim?

Cheers.

I think it's a typo: 'seminal', but the 's' is missing.

Ok, this is what the Mirriam Webster dictionary has on seminal:

So, what's a seminal question?

Cheers.

I like the way we "stay on message" here. I did mean "seminal" question, but can't type worth beans, and proof read everything I send 3 or 4 times. But that kind of mistake still gets out. The "seminal question" is the "original" question I started this with (see your own posted definition for seminal). What's wrong with the standard solar model?

I thought I already said that. Of course it does.

The problem is that you & I do not mean the same thing when we say big deal. You think it means that the standad model is in serious danger. I don't, and neither do the authors of any of the papers you cite. To them, it's a big deal because they have much confidence in their ability to derive abundances spetroscopically, so the discrepancy is a real problem in that context. But it is nowhere near the level of importance (at least not yet) to place the standard solar model in any danger of falsification.
The evidence for the tachocline being the most likely place to generate the magnetic field comes from plasma physics, and there is no short answer to the question that I can put here, beyond that. You will find it explained in Mestel's book Stellar Magnetism, or in the solar pla