The sun, as a massive ball of hot gas, undergoes a process known as nuclear fusion, where hydrogen atoms combine to form helium and release a tremendous amount of energy. This process has been ongoing for about 4.6 billion years and will continue for several billion more years.
However, if by “burn down” you are referring to the eventual end of the sun’s life cycle, it will not burn in the sense of a flame extinguishing. Instead, it will undergo significant changes over time. The sun is currently in the main sequence phase, where it fuses hydrogen into helium in its core. As the hydrogen in the core gets depleted, the sun will gradually expand into a red giant.
Scientists predict that in approximately 5 billion years, the sun will exhaust its hydrogen fuel and begin fusing helium. During this phase, it will expand and become much larger, engulfing the inner planets of our solar system, including Earth. Eventually, the sun will shed its outer layers, leaving behind a dense core called a white dwarf.
So, rather than “burning down,” the sun will go through a series of stages, culminating in the formation of a white dwarf.