|MadSci Network: Astronomy|
Nuclear weapons are controlled experiments, so we can measure directly what happens. In a nuclear explosion, the bomb material and surrounding area get extremely hot. The hotter objects are, the more short-wavelength radiation (in this case, X-rays) they emit. So it is possible to measure the big flux of X-rays the moment the bomb goes off. Inside the Sun, we cannot see this radiation because it is quicky absorbed by the surrounding material. We do know that the interior of the sun MUST be hot or else it would be unstable. If the core of the sun were too cool, the sun would contract; conversely, if the core of the Sun got too hot, it would expand. We know the sun is stable, and that means that the very core of the Sun has to at a temperature of about 10 million degrees. Under these conditions, hydrogen is being fused to make helium. One of the products of these reactions is the emission of neutrinos, which are very low-mass chargeless elementary particles. We have detectors on the Earth that can see these neutrinos, confirming that the Sun has nuclear reactions going on, and thereby confirming the high temperatures in the Sun.
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