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This combination of circumstances produces an outer convection zone, the top of which is visible in the Sun as solar granulation. Low-mass main-sequence stars, such as red dwarfs below 0.35 solar masses, [3] as well as pre-main sequence stars on the Hayashi track, are convective throughout and do not contain a radiation zone. [4]
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.
In solar physics and observation, granules are convection cells in the Sun's photosphere. They are caused by currents of plasma in the Sun's convective zone , directly below the photosphere. The grainy appearance of the photosphere is produced by the tops of these convective cells; this pattern is referred to as granulation .
For example, in the Sun the convection at the base of the convection zone, near the core, is adiabatic but that near the surface is not. The mixing length theory contains two free parameters which must be set to make the model fit observations, so it is a phenomenological theory rather than a rigorous mathematical formulation.
The core of the Sun is considered to extend from the center to about 0.2 of the solar radius (139,000 km; 86,000 mi). [1] It is the hottest part of the Sun and of the Solar System. It has a density of 150,000 kg/m 3 (150 g/cm 3) at the center, and a temperature of 15 million kelvins (15 million degrees Celsius; 27 million degrees Fahrenheit). [2]
Illustration of different stars' internal structure based on mass. The Sun in the middle has an inner radiating zone and an outer convective zone. The radiative zone is the thickest layer of the Sun, at 0.45 solar radii. From the core out to about 0.7 solar radii, thermal radiation is the primary means of energy transfer. [74]
The Sun rotates slowly enough that a spherical, non-rotating model is close enough to reality for deriving the rotational kernels. Helioseismology has shown that the Sun has a rotation profile with several features: [47] a rigidly-rotating radiative (i.e. non-convective) zone, though the rotation rate of the inner core is not well known;
The convection zone of a star is the range of radii in which energy is transported outward from the core region primarily by convection rather than radiation. This occurs at radii which are sufficiently opaque that convection is more efficient than radiation at transporting energy.