What is the primary energy source of the Sun?

The primary energy source of the Sun is nuclear fusion, which is the process where hydrogen nuclei combine under extreme pressure and temperature in the Sun's core to form helium nuclei. This fusion process releases an enormous amount of energy in the form of electromagnetic radiation, including visible light and heat.

Nuclear fusion is crucial to the Sun's structure and energy output; it produces energy in a way that balances the gravitational forces pulling inward with the outward pressure generated by the energy produced. This balance is what keeps the Sun stable over billions of years. The fusion process also accounts for the creation of other elements over time within the stellar lifecycle.

Gravitational energy does play a role in the overall process by keeping the Sun’s mass intact and contributing to the high temperatures necessary for fusion, but it is not the primary energy source itself. Chemical reactions do not occur at a rate or scale in stars like the Sun that would contribute significantly to their energy output, as they are much less efficient than nuclear processes.