Solar Core - Energy Production

Energy Production

About 3.6×1038 protons (hydrogen nuclei) are converted into helium nuclei every second, releasing mass and energy at the mass-energy equivalence rate of 4.3 million tonnes per second, 380 yottawatts (3.8×1026 watts), equivalent to 9.1 ×1010 megatons of TNT per second.

The core produces almost all of the Sun's heat via fusion: the rest of the star is heated by the outward transfer of heat from the core. The energy produced by fusion in the core, except a small part carried out by neutrinos, must travel through many successive layers to the solar photosphere before it escapes into space as sunlight or kinetic energy of particles.

The energy production per unit time (power) of fusion in the core varies with distance from the solar center. At the center of the Sun, fusion power is estimated by models to be about 276.5 watts/m3.

The power production density of the core overall is similar to the metabolic production density of a reptile. The peak power production in the Sun's center, per volume, has been compared to the volumetric heat generated in an active compost heap. The tremendous power output of the Sun is due not to its high power per volume, but rather to its gigantic size.

The low power outputs occurring inside the fusion core of the Sun may also be surprising, considering the large power which might be predicted by a simple application of the Stefan–Boltzmann law for temperatures of 10 to 15 million degrees kelvin. However, layers of the Sun are radiating to outer layers only slightly lower in temperature, and it is this difference in radiation powers between layers which determines net power production and transfer in the solar core.

At 19% of the solar radius, near the edge of the core, temperatures are about 10 million degrees kelvin and fusion power density is 6.9 watts/m3, which is about 2.5% of the maximum value at the solar center. Some 91% of the solar energy is produced within this radius. Within 24% of the radius (the outer "core" by some definitions), 99% of the Sun's power is produced. At 30% of the solar radius, the rate of fusion is almost nil.