AST 115 1st Edition Lecture 20 Outline of Last Lecture I. Features of the Suna. Atmosphereb. PhenomenaII. Explanation of the Solar Cyclea. Babcock or Dynamo TheoryIII. Physical Properties of the SunOutline of Current Lecture I. The Source of the Sun’s Energya. PossibilitiesII. The Proton – Proton Chain a. Deuteronb. Positronc. NeutrinoIII. The Solar Neutrino “Mystery”a. Raymond Davisb. What’s wrong?Current Lecture The Source of the Sun’s Energyo Possibilities:- Chemical burning? The chemical makeup of the Sun = Hydrogen and Helium. Helium cannot burn, but hydrogen can burn. Hydrogen gas is at a very high temperature in the Sun; it is not capable of burning because it is ionized (not in the proper state to burn). Also, in order for These notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.hydrogen to burn (if it was in the proper state), oxygen is needed. There are very small traces of oxygen in the Sun, but it is also not in the proper state to help the hydrogen burn. [DOES NOT WORK]- Gravitational contraction? The Sun would have had to contract down to the size of a baseballlong ago in order to harbor this much energy. [DOES NOT WORK]- Nuclear Energy? Fission = a heavy nucleus “splits” and releases energy. [DOES NOT WORK] Fusion = low mass nuclei “join” together and release energy. [SEEMS TO BE THE ANSWER]There are plenty of low mass nuclei inside the Sun. It is possible for them to “join” and release energy.E=mc2E = energy, m = mass, c = speed of lighto The source of energy for the Sun (and for normal stars):- Thermonuclear Fusion of Hydrogen into Helium This occurs only at extremely high temperatures. Hydrogen = the input and Helium = the output A portion of the mass of the hydrogen is converted into energy according to Einstein’s famous equation (E= mc2) In order for this to happen, it requires that 600,000,000 tons of hydrogen nuclei (protons) fuse each second to form 596,000,000 tons of helium nuclei (not atoms!) with 4,000,000 tons converted to energy each second! The Proton – Proton Chain (or Cycle)1) proton + proton → deuteron + positron + neutrino2) proton + deuteron → helium-3 + gamma ray * helium-3 = light helium (not the same as helium in balloons, helium-4)3) helium-3 + helium-3 → helium-4 + (2) protons * helium-4 = same type of helium used in balloonso This chain/cycle (#1-3) is the recipe for hydrogen fusion in the Sun.o Positron = positive electrono Neutrino = no charge, no mass, always travels at the speed of light (“little neutral one”)o Deuteron = particle that stands by itself, but has a proton and neutron embeddedinside of it. The Solar Neutrino “Mystery”o There should be extremely large numbers of solar neutrinos passing through Earth at all times.o Neutrinos are produced in the first step of the Proton – Proton Chain. They are very hard to detect. Chlorine is a little better at stopping neutrinos.o Raymond Davis built a solar neutrino detector from a tank of 100,000 gallons of dry-cleaning fluid in an old mine 1 mile underground in South Dakota.o He found only about 1/3 of the predicted number of solar neutrinos.o What’s wrong? Why was only 1/3 of the predicted number of solar neutrinos found?- Theory of fusion in the Sun? [NO]- Detector system? [NO]- Our understanding of neutrinos? [YES] There are three types of neutrinos. They have very small mass, travel just less than the speed of light, and they change between types – they are transformers. This explains why Raymond Davis found only 1/3 of the predicted number of solar neutrinos in his experiment. He was only looking for one out of the three types of
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