what is fusion and what are the zones of a star and their properties?
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hey im currently doing Physics GCSE (P7) and i am quite confused about fusion and the zones of a star. any help about either of these topics would be great,
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The simple definition for nuclear fussion is the joining together of small atomic nuclei.
For example, two light nuclei, like the ones that hydrogen have, can fuse together to form an isotope of helium (as their are now 2 protons in one nucleus). Unlike nuclear fission which is used in nuclear power stations, nuclear fussion does not create any radioactive waste. However, it can only happen at really high temperatures, which is why it happens in stars.
The first stage of a star is a protostar. It is made from a cloud of gas and dust which spirals together due to the force of gravity. Next is the main sequence (the part our Sun is in). Here Gravitational energy is converted into heat energy and when the temperature is high enogh then hydrogen atoms undergo nuclear fussion and become helium atoms. This is a very long and stable stage. Now, stars around about the size of our sun turn into Red Giants and bigger stars turn to a red super giant. The hydrogen has now begun to run out and the surface cools so that it ends up turning red. Heavier elements are now being fused together. The bigger the star, the heavier the elements it is able to fuse together. However, the heaviest element that can be made at this point is iron.
At this point stars around about the size of our sun becomes so unstable that it ejects its outer layer of dust and gas as a planetary nebula and becomes a small, hot, dense white dwarf wich then becomes a black dwarf.
Bigger stars start glowing more brightly again as they undergo more fusion. They expand and contract several times. It then explodes in a supernova which fuses together the iron into eaven heavier elements and blasts them into space forming new planets and stars. This leaves a dense core called a neutron star. If the star was big enough then it will turn into a black hole