The radiative zone is the part of the sun?s interior that is between the inner core and the outer convective zone. In this zone, energy is efficiently transferred by photons to the surrounding region. The electromagnetic radiation of the radiative zone is the result of the energy of nuclear fusion at the core.
The radiative zone accounts for 45 percent of the sun?s radius. The core energy is carried outside as photons, which travel one micron before being absorbed by gas molecules. After the absorption of photons, the gas molecules heat up and emit additional photons of the same wavelength. The re-emitted photons move another micron and are absorbed by more gas molecules, and the cycle repeats. Nearly, 10^25 absorptions and re-emissions are estimated to occur before a photon to reaches the surface.
The part of the sun at the core and the radiative zone spin differently than the outer convective zone. The boundary between these two zones is called the tacholine. Stars that are cooler and smaller than the sun do not have radiative zones; instead, they have convective zones that extend to their cores. In larger stars, radiative zones appear to be larger, and convective zones appear to be smaller.