Final answer:
The energy from gravity is not enough to power the Sun. The primary source of the Sun's energy is nuclear fusion, specifically the fusion of hydrogen atoms to form helium.
Step-by-step explanation:
The energy from gravity is not enough to power the Sun because it is not a sustainable source of energy. While gravitational contraction can produce heat and energy, it is not sufficient to account for the Sun's total energy output. Scientists have found that the primary source of the Sun's energy is nuclear fusion, specifically the fusion of hydrogen atoms to form helium. This process releases a tremendous amount of energy, which is why the Sun can shine so brightly for billions of years.