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Work on the carbon/nitrogen cycle of massive stars


Stellar composition and energy production
Hans Bethe Scientist
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I came to that conference and was very astonished and pleased by Strömgren's long talks telling all of us about the internal constitution of stars and how it worked very well with hydrogen and helium, and that was very convincing. It was convincing also for another reason because with Eddington's old idea of a high temperature and the heavy atoms in the sun, he never could agree with the calculated opacity of material, opacity being the tendency of matter to absorb light and then to emit another quantum after the absorption. Now with the hydrogen helium it worked exactly right, the opacity was just what quantum theory predicted and so everybody was happy. Now, at the conference most of the discussion was about the build up of elements and I thought Weizsäcker had been there, but looking at the roster of the people at the conference, he wasn't there; it was Gamow reporting [for] Weizsäcker, and they had fantastic ideas that there should be neutrons made by beryllium and that would build up other elements and that all sounded to me wrong. In addition to that Strömgren made clear to us that heavier stars than the sun, for instance Sirius A, have a much higher energy production, not only total energy production but also energy production per unit mass. So one needed a nuclear reaction which would increase rapidly with increasing temperature. It was known from the theory of Eddington and Strömgren how the temperature would increase with the mass of the star, quite slowly, less than linearly with the mass of the star, and that was certainly not enough with the proton-proton reaction to explain the very high luminosity of brilliant stars like Sirius.

The late German-American physicist Hans Bethe once described himself as the H-bomb's midwife. He left Nazi Germany in 1933, after which he helped develop the first atomic bomb, won the Nobel Prize in Physics in 1967 for his contribution to the theory of nuclear reactions, advocated tighter controls over nuclear weapons and campaigned vigorously for the peaceful use of nuclear energy.

Listeners: Sam Schweber

Silvan Sam Schweber is the Koret Professor of the History of Ideas and Professor of Physics at Brandeis University, and a Faculty Associate in the Department of the History of Science at Harvard University. He is the author of a history of the development of quantum electro mechanics, "QED and the men who made it", and has recently completed a biography of Hans Bethe and the history of nuclear weapons development, "In the Shadow of the Bomb: Oppenheimer, Bethe, and the Moral Responsibility of the Scientist" (Princeton University Press, 2000).

Tags: Sirius A, Bengt Strömgren, Arthur Eddington, Carl von Weizsäcker, George Gamow

Duration: 3 minutes, 2 seconds

Date story recorded: December 1996

Date story went live: 24 January 2008