The Observant Astronomer

The passing scene as observed by an observant Jew, who daylights as an astronomer.

observantastronomer@yahoo.com

Tuesday, March 08, 2005

Hans Bethe Z"L

For those of you who like to debate the age of the universe, consider the following.

Until the late 57th century (i.e. early 20th C.E.) it was known that the Sun was billions of years old, but there was no known way to keep it shining so long. The timescale for energy released by gravitational contraction was way too short, and even if the Sun was mostly carbon, coal burning wouldn't help all that much.

It was Hans Bethe who, in 5698 (1938), showed that the fusion of 4 hydrogen nuclei into one helium nucleus could provide the required energy. As it turned out, the CNO-catalyzed reaction chain he originally proposed dominates in stars with higher masses than our Sun, but a more direct chain of reactions is the source of energy that has kept the Sun burning all this time. For this fundamental discovery, he was awarded the 1967 Nobel Prize in physics. (His Nobel Prize lecture presents a good summary of this work, even if you have to ignore the equations.)

3 Comments:

Blogger Rebeljew said...

"It was Hans Bethe who, in 5698 (1938), showed that the fusion of 4 hydrogen nuclei into one helium nucleus could provide the required energy."

How do the 4 protons and 0 neutrons work in this fusion to 2 and 2? What am I missing?

7:16 AM, March 09, 2005  
Blogger The Observer said...

How do the 4 protons and 0 neutrons work in this fusion to 2 and 2? What am I missing?The two beta decays where a proton decays into a neutron + positron + neutrino. The end result is that 4 protons become 1 helium-4 nucleus (2 p + 2 n), 2 positrons, two neutrinos and energy.

11:09 AM, March 09, 2005  
Blogger Zman Biur said...

And let's not forget his incidental role in one of the greatest puns in physics, the Alpher-Bethe-Gamow Theory!

2:19 AM, March 14, 2005  

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