Hot Stuff

Everyone takes it for granted that the sun will go on shining until he dies--and, as a matter of lesser interest, for a long time after he dies. Astrophysicists, who believe the solar star-stuff has been hot for billions of years and will be so for billions of years more, have long cudgeled their brains for a reason why. Most favored of recent theories is that hydrogen is the fuel. It is known that the sun does not "burn" hydrogen, in the sense of releasing stored chemical energy as from coal; it physically changes fragments of hydrogen atoms directly into radiation. But the question remains: Just what atomic processes enable the hydrogen to be utilized as fuel?

At a meeting of the venerable, rich American Philosophical Society in Philadelphia last week, grey, gentle Astronomer Henry Norris Russell of Princeton (see p. 58) explained what he considers the most reasonable modern theory on this question. The theory was worked out mathematically by Dr. Hans Albrecht Bethe of Cornell, a brilliant analyst of atomic behavior. Dr. Bethe sat down to figure out what atomic reactions would occur often enough to be important in the sun's energy economy, yet not so often as to use up the supply of some important ingredient in a hurry. He found that, at temperatures above 15,000,000DEG C., hydrogen atoms would attack carbon. The carbon atom would disappear for a while, but after a further series of reactions in which three more hydrogen atoms would be used up, the carbon would reappear, ready to be used again. Thus carbon, though not depleted itself, is the agent that annihilates hydrogen, creates energy. A use less end-product, or "ash," is helium gas.

One complete cycle withdrawing and returning a carbon atom to circulation requires more than 52,000,000 years. But such an enormous number of cycles are going on all the time that they keep the sun stuff hot.

An exile from Germany's University of Munich, demure Dr. Bethe at Cornell has increased his repute as an atomic theorist like a snowball rolling downhill. It is hard to pick up a physics journal nowadays in which he has not some new light to shed on old problems, or in which other physicists do not find occasion to cite his work. Dr. Russell in Philadelphia last week left no doubt that this new work on the sun is a highly valued contribution--from an astrophysical point of view, very hot stuff indeed.

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