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At the center of the Sun, fusion power is estimated by models to be about 276.5 watts/m 3. [7] 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 ...
The core of the Sun extends from the center to about 20–25% of the solar radius. [60] It has a density of up to 150 g/cm 3 [61] [62] (about 150 times the density of water) and a temperature of close to 15.7 million kelvin (K). [62] By contrast, the Sun's surface temperature is about 5800 K.
The Sun has a core temperature of around 15.7 × 10 6 K, and only 1.7% of 4 He nuclei produced in the Sun are born in the CNO cycle. The CNO-I process was independently proposed by Carl von Weizsäcker [5] [6] and Hans Bethe [7] [8] in the late 1930s.
In main sequence stars more than 1.3 times the mass of the Sun, the high core temperature causes nuclear fusion of hydrogen into helium to occur predominantly via the carbon-nitrogen-oxygen (CNO) cycle instead of the less temperature-sensitive proton–proton chain. The high temperature gradient in the core region forms a convection zone that ...
In the Sun, the region between the solar core at 0.2 of the Sun's radius and the outer convection zone at 0.71 of the Sun's radius is referred to as the radiation zone, although the core is also a radiative region. [1] The convection zone and the radiative zone are divided by the tachocline, another part of the Sun.
The dashed line shows the combined energy generation of the PP and CNO processes within a star. At the Sun's core temperature of 15.5 million K the PP process is dominant. The PP process and the CNO process are equal at around 20 MK. [1] Scheme of the proton–proton branch I reaction
The minimum temperature required for stellar hydrogen fusion exceeds 10 7 K (10 MK), while the density at the core of the Sun is over 100 g/cm 3. The core is surrounded by the stellar envelope, which transports energy from the core to the stellar atmosphere where it is radiated away into space. [1]
This temperature is achieved in the cores of main-sequence stars with at least 1.3 times the mass of the Sun. [32] The Sun itself has a core temperature of about 1.57 × 10 7 K. [33]: 5 As a main-sequence star ages, the core temperature will rise, resulting in a steadily increasing contribution from its CNO cycle. [25]