I have a test in astrophysics coming up and this is something I should be able t
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I have a test in astrophysics coming up and this is something I should be able to do. If possible can I get help answering the question but also an outline for how to answer general questions like this - important and relevant equations and formulas and steps- important concepts etc.. using this question as a basis for studying for the test and for designing a 'cheat sheet'
11. Why doesn't hydrogen fusion run-away making a star blow up like a hydrogen bomb (understand the arguments behind the safety valve mechanism). Why is the tempera- ture in the core of a main sequence star only weakly dependent on the mass of a main sequence star?Explanation / Answer
ANSWER OF FRIST QUESION : Why doesn't hydrogen fusion run-away making a star blow up like a hydrogen bomb.
The temperature and pressure everywhere inside the Sun reach the critical point to start nuclear reactions - there is no reason for it to take such a long time to complete the reaction process.
Just like a nuclear bomb will complete all the reaction within 10-6 seconds.
There are four factors involved: (1) velocity distribution of the nuclei; (2) small geometrical cross-section for head-on collisions of nuclei; (3) quantum-mechanical tunneling probability; (4) for the p-p reaction, a weak-force effect is required.
The bottleneck in Solar fusion is getting two hydrogen nuclei, i.e. two protons, to fuse together.
Protons collide all the time in the Sun's core, but there is no bound state of two protons because there aren't any neutrons to hold them together. Protons can only fuse if one of them undergoes beta plus decay to become a neutron at the moment of the collision. The neutron and the remaining proton fuse to form a deuterium nucleus, and this can react with another proton to form 3He3He. The beta plus decay is mediated by the weak force so it's relatively slow process anyway, and the probability of the beta plus decay happening at just the right time is extremely low, which is why proton fusion is relatively slow in the Sun. It takes gazillions of proton-proton collisions to form a single deuterium nucleus.Nuclear fusion weapons bombs fuse fast because they use a mixture of deuterium and tritium. They don't attempt to fuse 1H1H so they don't have the bottleneck that the Sun has to deal with.This is why it want's do as hydrogen bomb do.
ANSWER OF SECOND QUESTION:Why is the temperature in the core of a main sequence star only weakly dependent on the mass of a main sequence star:
Main sequence stars fuse hydrogen atoms to form helium atoms in their cores. About 90 percent of the stars in the universe, including the sun, are main sequence stars. These stars can range from about a tenth of the mass of the sun to up to 200 times as massive.How long a main sequence star lives depends on how massive it is. A higher-mass star may have more material, but it burns through it faster due to higher core temperatures caused by greater gravitational forces. While the sun will spend about 10 billion years on the main sequence, a star 10 times as massive will stick around for only 20 million years
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