The star is a ball of hot gases containing different kinds of elements at different cores. It has a very high temperature that radiates all throughout the galaxy. The star has four main parts; the core, photosphere, chromospheres and corona. The outer core of a star located at the chromospheres contains mostly of hydrogen. Inside the hydrogen is helium then carbon, oxygen, neon, magnesium silicon and the inert gas. When a star releases energy it is due to the thermonuclear fusion of hydrogen into helium. So the answer is fusion.