Long-Term Solar Oscillations and the Age of the Sun

Introduction

In the June 1996 edition of the Acts & Facts series published by the Institute for Creation Research, Keith Davies-former Administrator of Scarborough Christian Academy in Ontario, Canada, now retired-presents an essay which argues that the sun is homogeneous in structure and derives its energy from gravitational contraction, making it "an exceedingly young" star (Davies 1996). He describes three pieces of evidence to support his argument. The first is a long-term solar oscillation of two hours and forty minutes (160 minutes), the second is the solar neutrino problem and the third is the observed abundances of lithium and beryllium. If it were true that the sun is a young star, this would have profound implications for the age of the solar system, stellar evolution, and possibly even cosmology as a whole. Therefore, it is worth examining Davies' argument to see if his claims are supported by the facts.

Of the evidence Davies describes, the strongest is the long-term solar oscillation. The other two are minor, and they lose their strength if the oscillation evidence is false. Therefore, this essay will consist primarily of an examination of the 160 minute oscillation, and I will be critiquing his evidence rather than examining the validity of his argument. When he published his essay in 1996 this evidence was already twenty years old, so even if he had presented it properly, more up-to-date data could have superceded it by then. I will describe some of this new data at the end of my discussion, but I will also show that Davies in fact misused his sources by presenting distorted information to support his thesis.

Solar Oscillations

Prior to the 1970s, if anyone had suggested that the sun could vibrate like a sphere of gelatin, the vast majority of astrophysicists would have strenuously disagreed. The main reason was that no one could conceive of a force that could start such oscillations, much less keep them going. A few researchers had suggested they might exist and that they might be observable, but R. H. Dicke did not verify their existence until 1973 (Moore and Hunt 1983, p72). Since then it has been deduced that solar oscillations are caused by interactions between the plasma that makes up the sun on the one hand, and gravity and pressure changes on the other.

There are three types of oscillations. Pressure modes are sound waves trapped in the temperature gradient. A crude analogy would be an echo bouncing around inside a cavern. Fundamental modes are caused by gravitational interactions with the sun's surface and resemble ocean waves. One type of fundamental mode is called a mode, because it changes the observed radius of the sun. Gravity modes are not completely understood, but they are believed to be the result of buoyancy effects. All the known pressure and fundamental modes (some 10 million) have oscillation periods of less than 18 minutes, and most are around 5 minutes. The gravity modes are not known conclusively to exist, but they are predicted to have periods of 40 minutes or longer. [Readers who wish to learn more are encouraged to read a series of articles in Science 1996 May 31; 272.]

Davies claims that if the sun had a large and massive core as predicted by the standard models of solar structure and evolution, then this core "would have a substantial effect on any global oscillations." He explains that "such a large core would mean that the Sun's [sic] global oscillations would range up to a maximum fundamental radial mode of oscillation of around one hour." He then adds that fundamental "[o]scillations greater than one hour would involve such enormous amounts of energy that they would result in the complete disruption of any large core that might be present in the Sun." In contrast, however, he states that for "a very young homogeneous star that has not yet developed a large central core... its spectrum of global oscillations have been calculated" to be as high as 167 minutes. In fact, he claims that this is "a key distinguishing feature of a young homogeneous star."

He then cites two 20-year-old papers (Brookes and others 1976; Severny and others 1976) whose authors independently report detecting a 160-minute oscillation that both research groups believed was a fundamental radial mode oscillation. Both groups also concluded that, if this oscillation was real, it would be nearly consistent with a homogeneous model of the sun. In conclusion, Davies cited three other astronomers to deliver the coup de grace. He quotes Iain Nicholson (Moore and Hunt 1983, p72) as saying that if this oscillation "was a true fundamental period, then the 'standard model could not be correct.'" And he cites a paper by J. Christensen-Dalsgaard and D.O. Gough (Christensen-Dalsgaard and Gough 1976) that appears in the same journal which carries the reports of the 160-minute oscillation. He quotes them as saying that "in order to account for the 2 hour 40 minute observation it is 'evident that a very drastic change in the solar model would be necessary' and 'it is unlikely that any such model can be found.'"

To summarize Davies' argument, if the sun is homogeneous, it cannot have a dense core; if it cannot have a dense core, it cannot obtain its energy from nuclear reactions; if it cannot obtain its energy from nuclear reactions, it must obtain it from gravitational contraction. And astronomers generally believe that young stars that have not yet reached the main sequence are homogeneous and obtain their energy from gravitational contraction. For Davies, the conclusion was obvious: "The fundamental oscillation of the Sun matches the model for a young star."

The Evidence

The major problem with the evidence he describes is that it is over two decades old. In and of itself, this is not a fatal problem, because if nothing new has been learned since then, the data is still valid, even if it is old. However, as I hope to show later, it is in fact obsolete because much new information has been learned, especially in the last ten years. And obsolete data is always invalid, no matter how much it supports a favorite hypothesis.

Furthermore, Davies did not treat his sources fairly. He commits three indiscretions that no careful or experienced scholar should commit. The first is misinterpretation. Part of Davies' argument is that a star with a massive central core cannot support fundamental oscillations with periods greater than one hour, because such vibrational modes would disrupt the core. (Keep in mind that whenever Davies refers to global oscillations in general or the 160-minute oscillation in particular he is referring to fundamental mode oscillations.) The source for this information is Nicholson (Moore and Hunt 1983, p72), but Davies' claim is based on an incorrect interpretation of what Nicholson actually said. Nicholson's statement is as follows:

[I]t has been pointed out that if the [fundamental mode] oscillations arise in the deep interior, then-because of damping mechanisms-the oscillations seen at the surface should be weaker than those in the interior. Attempts to calculate the oscillation magnitudes required to match the [surface] observations appear to indicate that they would become of such great amplitude that they would disrupt the solar interior.

Nicholson is referring to observed oscillations, not theoretical ones, and if you will recall from an earlier discussion, all known oscillations have periods less than one hour. As such, Nicholson is saying that any of the observed fundamental oscillations would be powerful enough to disrupt the core. Why this does not happen he did not explain, but it should be obvious that, despite Davies' claim, oscillations longer than one hour could be tolerated by the standard model just as the short-term oscillations are.

The second indiscretion is selective quotation and, in at least one case, outright misquotation. For example in the same source that Davies quotes as evidence of Nicholson's admission that 160-minute oscillations cannot be explained by the standard model, Nicholson writes, "the observed results seem roughly consistent with the way the Sun's interior is believed to be constructed." (Moore and Hunt 1983, p72) In reference to the 160-minute oscillation, Nicholson adds: "It seems certain there is some periodic effect to explain, but whether the oscillation is a true global oscillation or a surface effect, or a 'gravity wave' like waves in the ocean, remains a matter of debate." He then concludes: "No-one [sic] seriously doubts that the Sun shines by means of thermonuclear reactions converting hydrogen to helium, but the precise mechanism is open to doubt" (Moore and Hunt 1983:73). In other words, while Nicholson agrees that a 160-minute fundamental oscillation would contradict the standard model, he states that the long-term oscillation may not be fundamental at all, especially if all the other known oscillations confirm the standard model. Since none of these statements can even remotely be considered an endorsement of Davies' thesis, there is perhaps no mystery as to why he fails to mention them. Even so, it is dishonest for a scholar to quote a source in support of his thesis while at the same time ignoring statements showing that the source in fact comes to the opposite conclusion.

The one case of misquotation involves the quote from Christensen-Dalsgaard and Gough. Davies' statement implies that the authors believed it was impossible for the standard model to explain the long-term oscillation under any circumstances. What they actually say, however, is this:

It is also evident that a very drastic change in the solar model would be necessary to enable the 2 h 40 min oscillation to be interpreted as the fundamental radial mode, as Severny et al.and Brookes et al. suggest. Indeed it is unlikely that any such model can be found that can generate the observed photon luminosity by thermonuclear reactions [emphasis added] (Christensen-Dalsgaard and Gough 1976, p90).

In other words, the authors are saying that drastic changes would be necessary only if the long-term oscillation is a fundamental mode oscillation, and that only under such circumstances would it be impossible to construct a model that relies on stellar fusion. As I hope to demonstrate later, Christensen-Dalsgaard and Gough did not believe it was a fundamental mode oscillation.

Davies' refusal to discuss alternative explanations is in fact his third indiscretion. Such explanations do exist if for no other reason than the fact that the very sources he cites mentions them. Though both of the twenty-year old papers clearly interpret their results based on a homogeneous model, both discuss other interpretations as well. In the conclusion of Severny and others, the authors "...investigated two possible solutions...." The first is that "nuclear... reactions are not responsible for energy generation in the Sun," which Davies seizes upon to support his claim that the sun is young. The second possible solution, however, allows them "...to adopt the current model of solar structure with [nuclear] reactions and assume that [they] really observe not pure radial pulsations but some gravity g mode of quadrapole oscillation." They go on to say that "g modes... can yield long period oscillations," and admit that one mode in particular, the g11 mode, is "in perfect agreement" with their observed period, though they do question the dominance of such a high harmonic. However, they also admit that their method of observation does not allow them to "distinguish pure radial pulsations from quadropole oscillations." As such, while they maintain that a homogeneous model is the "best" interpretation, they do allow for the possibility that other explanations are possible. Davies conveniently omits this caveat.

In Brookes and others(1976), the authors do not mention nuclear reactions, though Davies claims that they, too, reject the idea that the sun is powered by fusion reactions. However, they also admit that their observations could be explained by high-order gravity modes. They also cite another paper that describes observations they found "difficult to reconcile" with their own work, "unless the oscillations are of high order." (See Brookes and others 1976, p95, for citation.) This suggests that they are willing to accept the possibility of high-order oscillations, even though they found it difficult to do so. Once again, however, Davies ignores this alternative explanation.

Christensen-Dalsgaard and Gough also suggest an alternative to abandoning nuclear fusion. In fact, the entire section leading up to the statement Davies misquotes is an attempt to determine whether other modes could assume the standard model and still explain the observed long-term oscillation. They calculate periods for 38 pressure modes and 12 gravity modes using the standard model for values of spherical harmonic degree (l) equal to 0, 2 and 4, and values of initial heavy element abundance (Z) equal to 0.02 (the accepted value) and 0.04. Two gravity modes yielded oscillations nearly equal to those determined by the Soviet and British astronomers: g10 (l = 2, Z ( 0.02) with a period of 2 hours 34 minutes, and g11 (l = 2, Z = 0.04) with a period of 2 hours 39 minutes (Christensen-Dalsgaard and Gough 1976, p91). The authors caution that their calculations are not "sufficiently reliable"; nonetheless, they are reasonably confident that their results suggest that the 160-minute oscillation reported in the twenty-year old papers was due to a gravity wave (Christensen-Dalsgaard and Gough 1976, p90; Weiss 1976, p78).

Even Nicholson suggests an alternative explanation (Moore and Hunt 1983, p73). He begins by stating that "[m]ore recent analyses [no reference given] of the 2 hr 40 min oscillation suggest that it could be accounted for by reducing the core temperature by about 10 percent." He notes that this cannot account for the current solar luminosity, but he gets around this problem by suggesting that "the output of energy from the core fluctuates over long periods of time." In this way, since photons take ten million years to reach the surface of the sun, he suggests that the current luminosity could be the result of a more energetic past. Though few astrophysicists are willing to entertain the idea of core variability, it remains a viable, if unlikely, explanation. [Just recently, however, new data acquired from the SOHO satellite suggests that the core may indeed be cooler than originally thought, so core variability may not be so fantastic after all (Cowen 1998, p279).] Besides, it is dishonest for a scholar to ignore alternative explanations discussed by his sources, even if he believes they are not valid.

Helioseismology

Today, astronomers acknowledge that there are mysteries surrounding the sun that could have profound implications for our models of solar structure and activity (Lang 1996a, 1996b), and that among these are solar oscillations. However, these very same oscillations are being used to fine-tune the standard model by measuring how their speeds change as they pass through the sun's various layers (Lang 1996b). This powerful tool is known as helioseismology, and it is capable of directly probing nearly the entire volume of the solar interior in a way that no other observational method can. Davies himself admits that helioseismology can "provide important information on the structure of the Sun." It is in fact one of the great success stories of modern astronomy, because each of the thousands of known oscillations has been matched to the standard model with an accuracy of between four and five decimal places. This is an impressive feat for any complex model of stellar evolution (Scherrer 1996, 1997).

The point is that, despite Davies' claims to the contrary, helioseismology and associatied oscillations have all but confirmed the standard model for the structure of the sun (see especially Lang 1997). There is now no doubt that the sun possesses a large, dense central core capable of supporting fusion reactions. This in turn has also confirmed the standard model for solar evolution, because there are very few ways that a star with the sun's mass and elemental composition can evolve to its present state, even if it had been supernaturally created only a few thousand years ago (Graps 1997). It is rather ironic that the very phenomenon that Davies hopes will refute the ancient age of the sun has instead confirmed it.

However, the long-term solar oscillation problem is far from solved. Observations made in the 1980s had partially confirmed the observations made in the 1970s (Scherrer and others 1992; Kotov and others 1992), though it is interesting that Davies makes no mention of any of these other observations. These observations set an upper limit to the frequency of any long-term oscillations, which, perhaps not coincidentally, was 160 minutes. Even so, the astronomers making the observations were convinced that such long-term oscillations must be the result of gravity mode pulsations.

However, because these observations did not conclusively establish the existence of gravity mode oscillations, some researchers dismissed them as either atmospheric effects or an artifact of the earth's movement in solar orbit. If long-period oscillations do exist, then the ground-based GONG system (Global Oscillation Network Group) and the SOHO satellite (Solar and Heliospheric Observatory) should be able to detect them. So far they have failed to do so, though this may be due to technical problems (Lang 1996c)]. Though some astronomers still believe they may exist, the GONG and SOHO observations (or lack thereof) have convinced others that gravity mode oscillations are impossible (Scherrer 1997). Yet believer and skeptic alike agree that long period oscillations pose no threat to the validity of the standard model.

Solar Neutrinos

Another issue Davies uses to show that the sun is young is the solar neutrino problem. Neutrinos are subatomic particles released during stellar fusion. A certain flux (number per unit of time per area) is expected to flow from the sun continuously, but current measurements indicate that only one-third of the expected flux is observed. Severny and others (1976, p89) claim that this flux agrees with one of their possible solutions-that nuclear reactions are not responsible for the sun's energy-a position Davies endorses.

Nicholson, however, notes that the same 10% decrease in core temperature which could account for the long-term oscillation would also account for the low neutrino flux (Moore and Hunt 1983, p71). And while the current luminosity indicates that the core was more energetic in the past, the measured neutrino flux could represent the currently lower level of core activity. It has just recently been verified that neutrinos do have mass (Anonymous 1998). In theory, if neutrinos have mass then they can interact with matter which could cause them to change from one type of neutrino to another. This is known as neutrino oscillation, and it can reduce the flux produced by the core.

The point that Davies missed, however, is that a neutrino flux of any amount is strong evidence that the sun is in fact being powered by nuclear fusion. Gravitational contraction would not be expected to produce any neutrinos at all, because energy is produced by the conversion of gravitational potential energy first into kinetic energy and then into heat energy. No nuclear reactions are involved, so no neutrinos would be produced. The flux currently measured is too high to be derived from radioactive decay (and in any event the sun is of the wrong spectral type and is not massive enough to contain that much radioactive material), so the only possible source must be fusion reactions. Moreover, considering that only a small decrease in core temperature is needed to explain the current flux measurement (contrary to Davies' claims), solar neutrinos should be seen as a verification of the standard model rather than a refutation.

Conclusion

Based on this discussion, I believe that Davies is both naive and premature to propose that long-term oscillations indicated that the sun must be homogeneous, that it must be getting its energy from gravitational contraction, and especially that it must therefore be young. For one thing, we have seen how other types of oscillations have confirmed the standard models of solar structure and evolution, thus completely refuting Davies' claims. For another, there is still no evidence that long-term oscillations are real.

Davies must know his sources are outdated, but uses them anyway because they support the conclusion he wants to make. Just as important, however, these claims are based on distorted and misinterpreted information. Especially egregious is his omission of alternative explanations, because even those scientists who suggest that the sun is homogeneous admit that there are viable alternative explanations that could explain these oscillations without abandoning the standard model. And none of the sources he cites suggest that their evidence shows the sun is young; this is obviously Davies' own conclusion, based more on his reliance on biblical literalism than on hard science.

An obvious question to ask at this point is why Davies uses arguments that are so obviously in error? That is a difficult question, and only Davies can answer it with any certainty. He seems intelligent and learned enough to recognize that both his sources and the vast majority of more recent data really do not support his conclusions. However, it is also clear that standard scholarship practices would require that Davies abandon his view that the sun is a young, homogeneous star and in violation of the standard model. Even some of those solar researchers whose work from the 1970s Davies cited have reached this conclusion in the face of new data.

Therefore, I believe it is safe to conclude that, despite his pretense to the contrary, Davies is not interested in thoughtfully exploring an interesting solar phenomenon, but simply in justifying a narrowly constructed and somewhat naive literalistic belief. And while the subject he chose to discuss is quite fascinating, it is really just a minor mystery that tells us more about the state of creation science than it does about the age of the universe.

Acknowledgments

I would like to thank Alan M. MacRobert of Sky & Telescope, Prof. Kenneth R. Lang of Tufts University, and Prof. Philip Scherrer, Deborah Scherrer and Amara Graps of Stanford University for their helpful insights into this issue.