Is gravitational mass additive?Edit
Gravitational mass deep inside does radiate and the radiation propagate through the outside material to the surface. If the material is saturated, gravitational mass, that is, radiational pressure is additive. Even though not, Steady state partial radiational pressure is additive on the surface. Actual inside temperature is rather high.
Energy conservation approachEdit
Energy is proportional to gravitational mass,
where Cm is specific heat.
Energy is additive. but Cm is dependent on density.