What fundamental process enables the Sun to generate light and heat?

Nuclear fusion

The Sun functions as a massive, natural nuclear reactor where nuclear fusion is the primary engine of energy production. This process involves forcing hydrogen atoms to combine under conditions of extreme heat and pressure to form helium. Unlike chemical combustion which relies on rearranging molecular bonds and oxygen, this process involves a subatomic reconfiguration of matter itself, where the resulting helium atom has slightly less mass than the initial hydrogen nuclei. This transformation of mass into energy is what provides the immense heat and light observed across the solar system, sustaining life on Earth and maintaining the Sun's stability for billions of years.