[Image of Sun]

The Solar Interior

The core is the inner most region of the sun. Where the conversion of hydrogen and helium takes place via the proton-proton chain mechanism. The proton-proton chain is a three step process:

  • Two protons collide to produce Deuterium, a helium-3 nucleus and a gamma ray.
  • A proton collides with Deuterium to produce a helium-3 nucleus and a gamma ray.
  • Then Two Helium-3 collide to produce helium-4 and release two protons.

The radiative zone extends from the outer edge of the core to the Tachocline. The radiative zone gets its name from the method of energy transport by thermal radiation. This involves photons being emitted and reabsorbed by the ions in the zone repeatedly. Though the photons are travelling at the speed of light, it takes about a million years for a photon to travel out to the Tachocline. The density drops from 20 g/cm³ (about the density of gold) down to only 0.2 g/cm³ (about a 5th the density of water) from the bottom to the top of the radiative zone.

This interface layer lies between the radiative zone and the convective zone. The fluid motion gradually increases as you travel further out to the convection zone. It is now believed that the Sun's magnetic field is generated by a magnetic dynamo in this layer. The changes in fluid flow velocities across the layer (shear flows) from going from the radiative zone to the convective can stretch magnetic field lines of force and make them stronger. This change in flow velocity gives this layer its name Tachocline.

The convection zone is the outer-most layer of the solar interior. At the base of the convection zone the temperature is about 2,000,000 K. This is "cool" enough for the heavier ions (such as carbon, nitrogen, oxygen, calcium, and iron) to hold onto some of their electrons. This makes the material more opaque so that it is harder for radiation to get through. This traps heat that ultimately makes the fluid unstable and it starts to convect. Convection occurs when the temperature gradient (the rate at which the temperature falls with height or radius) gets larger than the adiabatic gradient (the rate at which the temperature would fall if a volume of material were moved higher without adding heat). Where this occurs a volume of material moved upward will be warmer than its surroundings and will continue to rise further. These convective motions carry heat quite rapidly to the surface. The fluid expands and cools as it rises. At the visible surface the temperature has dropped to 5,430 K.