How do the gases in the sun contribute to the emission of light and thermal energy?

The gases in the sun, mainly hydrogen and helium, undergo nuclear fusion reactions in its core. These reactions release a tremendous amount of energy in the form of light and thermal energy. The high temperatures and pressures in the sun's core cause the gases to collide and fuse together, releasing energy in the process. This energy eventually makes its way to the sun's surface, where it is emitted as light and heat.