It may be a good idea to refer to the star flow chart presented in the last lecture. Hydrostatic equilibrium , or the balance between weight and gas pressure, is the mechanism that keeps a star from dissipating into space, or completely collapsing. Because the weight at the core of the star is very high, the pressure must be high as well. Under conditions of high temperature and density, fusion will take place. Fusion is the combining of light nuclei into heavy nuclei, and for elements lighter than iron, the fusion process will produce energy.
Fusion requires two positively charged particles to combine.
Like charges repel, but if you can get two positively charged things close together, another force, called the Strong Force, takes over and pulls them together. So high temperatures are necessary to get two positively charged things close enough together to combine. Part of the energy escapes the star and comes out of the surface as light. Radiation and convection are generally the important ways that the energy is transferred. Last week we learned, after weighing stars, that massive stars, especially those on the main sequence, are generally more luminous.