A radiative zone is a layer of a star's interior where energy is primarily transported toward the exterior by means of radiative diffusion and thermal conduction, rather than by convection.. Over this range, the temperature of the plasma drops from 15 million K near the core down to 1.5 million K at the base of the convection zone. This leads to a violation of the stability criterion and to the creation of the convection zone; in the sun, opacity increases by more than a tenfold across the radiative zone, before the transition to the convection zone happens.

Additional situations in which this stability criterion is not met are:

  • Large values of <math>L(r)/M(r)</math>, which may happen towards the star core's center, where M(r) is small, if nuclear energy production is strongly peaked at the center, as in relatively massive stars. Thus such stars have a convective core.
  • A smaller value of <math>\gamma_{ad}</math>. For semi-ionized gas, where approximately half of the atoms are ionized, the effective value of <math>\gamma_{ad}</math> drops to 6/5,
  • Solar and Heliospheric Observatory — Sun 101 content on official site of this NASA and ESA joint project.