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The core of the Sun is considered to extend from the center to about 0.2 to 0.25 solar radius. It is the hottest part of the Sun and of the Solar System. It has a density of 150 g/cm³ (150 times the density of liquid water) at the center, and a temperature of 15 million degrees Celsius.〔http://solarscience.msfc.nasa.gov/interior.shtml〕 The core is made of hot, dense gas in the plasmic state (ions and electrons), at a pressure estimated at 265 billion bar (26.5 petapascals (PPa) or 3.84 trillion psi) at the center. The core inside 0.20 of the solar radius, contains 34% of the Sun's mass, but only 0.8% of the Sun's volume. Inside 0.24 solar radius, the core generates 99% of the fusion power of the Sun. There are two distinct reactions in which four hydrogen nuclei may eventually result in one helium nucleus: the proton-proton chain reaction – which is responsible for most of the Sun's released energy – and the CNO cycle. ==Energy conversion == Approximately 3.6 protons (hydrogen nuclei) are converted into helium nuclei every second releasing energy at a rate of 3.86 joules 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 conversion 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.〔(Table of temperatures, power densities, luminosities by radius in the sun )〕 Despite its intense temperature, the peak power generating density of the core overall is similar to an active compost heap, and is lower than the power density produced by the metabolism of an adult human. The Sun is much hotter than a compost heap due to the Sun's enormous volume. 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 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 generation and transfer in the solar core. At 19% of the solar radius, near the edge of the core, temperatures are about 10 million kelvin and fusion power density is 6.9 W/m3, which is about 2.5% of the maximum value at the solar center. The density here is about 40 g/cm3, or about 27% of that at the center.〔(see p 54 and 55 )〕 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. Beyond 30% of the solar radius, where temperature is 7 million K and density has fallen to 10 g/cm3 the rate of fusion is almost nil.〔( See )〕 There are two distinct reactions in which 4 H nuclei may eventually result in one He nucleus: "proton-proton chain reaction" and the "CNO cycle" ''(see below)''. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Solar core」の詳細全文を読む スポンサード リンク
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