Theenergy of stars comes fromnuclear fusion. This is a process that turns a lightIkhemikali into another heavier element. Stars are mostly made ofhydrogen andhelium. They turn the hydrogen into helium by fusion. When a star is near the end of its life, it begins to change the helium into other heavier chemical elements, likeI-carbon andI-oxygen. Fusion produces a lot of energy. The energy makes the star very hot. The energy produced by starsradiates away from them. The energy leaves aselectromagnetic radiation.
A star begins as a collapsing cloud of material made mostly ofhydrogen, withhelium and tiny amounts of heavier elements. Once the stellar core is dense enough, some of the hydrogen is changed into helium throughnuclear fusion.[1] The energy moves away from the core by a combination of radiation andconvection. The star's radiation stops it from collapsing further under its owngravity. Once the hydrogen fuel at the core has been used up, those stars with at least 0.4 times the mass of the Sun expand to become ared giant.
