geislunarsvæðinu

Geislunarsvæðið, often translated as the radiation zone, is a region within a star where energy generated by nuclear fusion in the core is transported outward through radiative diffusion. This process involves photons, the particles of light, being absorbed and re-emitted by the stellar plasma in a highly chaotic and indirect manner. Photons travel only a very short distance before interacting with a charged particle, losing some energy, and being scattered in a new direction. This constant absorption and re-emission means that energy can take hundreds of thousands or even millions of years to traverse the radiation zone.

The size and presence of a radiation zone depend on the star's mass. In stars like our Sun, the radiation zone is located between the core and the convection zone. In more massive stars, the radiation zone extends further out, while in less massive stars, convection may dominate throughout much of the interior, and a distinct radiation zone might be absent or very small. The temperature and density are highest in the core and decrease as you move outward. Within the radiation zone, these conditions are still sufficient for the plasma to be optically thick, meaning photons cannot travel far without interaction, necessitating the radiative transport mechanism. Beyond the radiation zone, in less dense and cooler regions, convection often becomes a more efficient way to transport energy.