According to current models of stellar evolution, when a star like our sun is very young, its enormous output of energy is provided by gravitational contraction. As it grows older, the models show that the source of its energy should change over to that of nuclear fusion as it slowly develops a very hot and dense core. Where exactly does our sun fit into this sequence?
The standard model of the sun assumes that it is around 5 billion years old and that it has already passed into its nuclear burning stage. This makes it all the more extraordinary that in 1976 a team of Russian astronomers, writing in the respected British scientific journal Nature showed how their research pointed clearly to the startling fact that the sun does not even seem to possess a large dense nuclear burning core. Instead, their results showed the sun as bearing the characteristics of a very young homogeneous star that corresponds with the early stages of the computer models.
The astronomers also proposed that nuclear reactions "are not responsible for energy generation in the sun." They said that such a conclusion, "although rather extravagant," follows from their own research into the analysis of the global oscillations of the sun and is quite consistent with two other major observational findings. They cited these other evidences as being the observed absence of appreciable neutrino flux from the sun, and the observed abundance of lithium and beryllium in the stellar atmosphere.
So not only did the team of astronomers propose the startling idea that nuclear reactions are not responsible for the source of the sun's energy, but they also put forward the equally startling concept that the sun, according to their data, could be homogeneous throughout. Both of these revolutionary ideas would fit in perfectly with the concept that the sun is a very young star.
All three of these major discoveries that point towards a young sun have since been confirmed by independent observations. This article will evaluate and update these findings and point the way to recent discoveries that show that the sun cannot possibly be the old nuclear burning, main-sequence star that it was once assumed to be.
The fundamental oscillation of the Sun matches the model for a young star.
In the same way that seismology gives us information about the structure of the Earth, so the relatively new discipline of helioseismology also provides important information on the structure of the sun. If the sun is an old star, then, according to the "standard model," it should have a large core reaching out to a distance of around 175,000 km from its center and having a density about fourteen times that of lead. A core of such a size and mass would, of course, have a substantial effect on any global oscillations of the Sun. In particular, the presence of such a large core would mean that the sun's global oscillations would range up to a maximum fundamental radial mode of oscillation of around one hour. Oscillations 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.
If, however, the sun is similar to a very young homogeneous star that has not yet developed a large central core, then its spectrum of global oscillations have been calculated as including a much longer fundamental radial oscillation of 2 hours 47 minutes, together with a non-radial fundamental oscillation of 59 minutes and either a second harmonic radial oscillation of 47 minutes or a 42 minute, non-radial second harmonic oscillation.
The predicted oscillation of 2 hours 47 minutes is particularly important as being a key distinguishing feature of a young homogeneous star.
The Russian astronomers were certainly startled to find that their observations of the sun were showing large and remarkably stable global oscillations with a period of 2 hours 40 minutes—very close to that predicted for a young homogeneous sun.
When trying to explain this quite unexpected observation, they stated in their article that a "most striking fact is that the observed period of 2 hours 40 minutes is almost precisely the same . . . as if the sun were to be an homogeneous sphere."
The concept of the sun's being an homogeneous sphere was so contrary to all previous ideas that the Russians were anxious to find alternative explanations. They kept on returning, however, to the conclusion that their work, which involved the observation of systematic fluctuations in very large portions of the sun's surface (comparable in size to the radius of the sun's disc) "points definitely to pulsations of the sun as a whole."
A British group soon confirmed the 2 hour 40 minutes oscillation. They also discovered further oscillations that included a 58 minute oscillation and a 40 minute oscillation. These three values are almost precisely those predicted for a homogeneous star of the same size and mass of the sun. When they published their results they stated that "Current solar models predict a period of about 1 hour corresponding to a steep density increase in the solar interior, in marked contrast to the observed 2.65-hour period, which is consistent with a nearly homogeneous model of the sun."
The unexpected observations have gone solidly against the predictions of the standard model of the sun. The solar astronomer Lain Nicholson, said of the long period oscillation that if it was a true fundamental period, then the "standard model could not be correct," and that the "central temperature of the sun would be less than half the conventional value." Such a low temperature would, of course, again fit in with the sun being a young star that has not yet achieved a sufficiently high temperature for main-sequence hydrogen burning.
The British astronomers J. Christenson-Dalsgaard and D.O. Gough commented 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."
This striking discovery of the sun's oscillations is not, however, the only evidence of a young sun.
The Solar Neutrino Emission is that of a young star.
The Russian team stated that the low neutrino flux, of the sun also fits in with their proposal that the energy of the sun did not come from nuclear sources.
The low neutrino flux is a well known and long standing problem for modern astronomy. A group of solar physicists, writing in the National Research Council publication Decade of Discovery, stated that the neutrino emission from the sun is "a problem that has worried astronomers for years" and that "the discrepancy is serious."
A low neutrino flux which results in a correspondingly low,  temperature of the sun's core, again fits in perfectly with the sun being a young star that has not yet achieved full nuclear burning of hydrogen, but is obtaining its energy from a slow gravitational contraction.
The Lithium and Beryllium abundance in the sun is consistent with that of a young star.
The article in Nature stated that "the abundance of lithium and beryllium in the solar atmosphere is another confirmatory evidence that nuclear energy is not responsible for the majority of the energy generation in the sun."
We know that lithium would be destroyed in around 7,500 years when the central temperature of a young star reaches 3 million degrees.
Observations show that the sun has already lost all but around one thousandth of its original abundance of lithium. This implies that if the sun had the expected initial abundance of lithium, then its central temperature must, of course, be at least 3 million degrees.
However, the sun still has its normal abundance of beryllium, which is destroyed at a temperature of 4 million degrees. If the Russian scientists are correct in assuming that the sun is homogeneous, then this means that the temperature throughout the whole sun must be far lower than the 15 million degrees required for the sun to be an old, main-sequence star.
RECENT SUPPORTING EVIDENCES
There are a great many confirmatory evidences for a young sun. One of the most recent was the announcement at a major scientific conference in 1995 that the temperature at the center of the sun seems to be varying over a period of several months. This is extremely hard to understand if the sun has a huge central core with a resulting enormous heat capacity. However, such rapid temperature changes are explicable if the sun is young and homogeneous. In such a situation there can be very rapid convective changes in temperature throughout the entire sun. (This idea will be developed in a future article.)
The three major observational evidences described in this article correlate with the expected characteristics of a young star that is obtaining its energy from gravitational contraction. The sun simply does not seem to have a large core that is very dense and has the high temperature that can sustain hydrogen nuclear burning. In other words, the sun definitely does not show the characteristics of a multi-billion-year-old star, but instead shows the characteristics of an exceedingly young star.
,  Severny, A.B., Kotov, V.A., and Tsap, T.T., 1976. "Observations of solar pulsations," Nature, vol. 259, p. 89.
 Ibid., p. 88.
 A typical description of the sun's core under the 'standard model' is that of Nicolson on p. 14 of The Sun published in 1982 by Michael Beazley, in association with the Royal Astronomical Society. Nicolson gives the sun's core as having a diameter of 350,000 km with a density of 160,000 kg /m^3 (about 14 times the density of lead.) This large core would extend outward to about 1/4 of the solar radius. The temperature of the core would be around 15,000,000 degrees K.
 Brookes, J.R., Isaak, G.R., and van der Raay, H.B., 1976. "Observation of free oscillations of the sun," Nature, vol. 259, p. 94. Also Nicolson, I., 1982. The Sun Publ. Michael Beazley p.84.
 Nicolson, op. cit., p. 84.
 Brookes et al., op. cit., p. 94.
, ,  Severny, op. cit., p. 88.
,  Brookes et al., op. cit., p. 94.
 Nicolson, op. cit., p. 84.
 Christensen-Dalsgaard, I., and Gough, D.O., 1976. "Towards a heliological inverse problem," Nature vol. 259, p. 90.
 National Research Council, 1991. The Decade of Discovery in Astronomy and Astrophysics National Academy Press, p. 34.
 Karttunen, H., Kroger, P., Oja, H., Poutanen, M., Donner, K.J., 1987. Fundamental Astronomy. Springer-Verlag, p. 273.
 Nicolson op. cit., p. 84.
 Severny, op. cit., p. 89.
 Hopkins, J., 1980. Glossary of Astronomy and Astrophysics. University of Chicago Press, p. 102.
 Karttunen, op. cit., p. 273.
 Stephens, S., "Needles in the Cosmic Haystack," Astronomy, September 1995, p. 53
 Karttunen, op. cit., p. 273.
 Chown, M., "The Riddle of the Solar Wind," New Scientist, 12th August 1995, p. 16.
* Keith Davies, M.S., Administrator, Scarborough Christian Academy, Ontario, Canada.
Cite this article: Keith Davies. 1996. Evidence for a Young Sun. Acts & Facts. 25 (6).