What is physically going on inside a star when it is on the main sequence?

What is physically going on inside a star when it is on the main sequence?|||The inside of a star is a churning mass of very hot gas. It churns in a manner not unlike a pot of boiling water on the stove. As you dive deeper the pressure and temperature increase until you reach the core. Here hydrogen atoms are being crushed together so strongly they suddenly and explosively join together to form helium. They resist this until forced by the heat and pressure around them. When two hydrogen atoms combine it happens all at once and huge amounts of heat and radiation are released. This is called "Fusion". It is this continuing fusion which gives the star its heat and light.





Eventually, of course, the hydrogen will be used up and the star will leave the main sequence to become a red giant.|||nuclear fusion is the short answer...|||Stable Hydrogen Fusion|||Hydrogen is being fused into helium by the proton-proton sequence in the center of a star while it is on the main sequence.





http://www.cliffsnotes.com/WileyCDA/Clif鈥?/a>|||Stars in the main sequence have a mass-luminosity relationship, and are fusing hydrogen into helium in the core.