What is nuclear fusion?

Answer 1 Fusion, in general, is the joining of light atomic nuclei to form heavier ones. They don't generate heat, but actually, need the energy to occur. These are endothermic reactions, so when a star has turned most of its fuel into iron, it undergoes a dynamic change. The star has lived its life up to now in equilibrium. The gravity that would pull it all together is balanced against the outward force of the energy liberated during exothermic fusion. At some point, the star will collapse. If a star is of insufficient magnitude, the collapse will signal that the star is in its last stages of life. But in stars of sufficient magnitude, there will be much more drama.

The collapse of sufficiently massive stars at the end of their iron forming stages will cause a supernova. Gravity is reclaiming the material, but it is also heating it during the collapse. This extra energy supplies sufficient heat for the fusion reactions that create elements heavier than iron up through uranium. These heavier elements are present on the earth, and they can have only come from a supernova event. The fusion reactions that create these heavy elements have tapped the heat energy created when the star collapsed.

The fusion process is detailed in a number of places. You'll find links below to investigate further.

Nuclear fusion is when two atoms fuse together to create a different atom. This can only occur under extreme conditions such as the conditions in the sun and many stars in our universe. The most common example of nuclear fusion is when two types of (known as isotopes of) hydrogen fuse together to create helium. The isotopes of hydrogen deuterium and tritium fuse to create helium. Deuterium contains one proton and one neutron and tritium contains two neutrons and one proton. Helium contains two protons and two neutrons so it takes the two protons it needs and the two neutrons it needs and spits out one neutron which is not needed. Nuclear fusion generates a huge amount of energy because it takes more energy to hold together two atoms then it does to hold together one. So it there is a lot of unneeded energy, which has to be released. Scientists believe that there used to be the only hydrogen in the universe but in the extreme conditions of the big bang, atoms fused together to create the atoms which are found in the universe today.

Answer 2 (A brief answer)Nuclear fusion is the merging of two light nuclei into one heavier nucleus. The resulting component total mass is less than the masses of the input nuclei. This mass defect changes into energy according to the mass-energy relation of Einstein (E=Mc2 ); E is the energy, M is the mass defect, c is the light speed. The joining of nuclei