As a protostar evolves from stage 4 to stage 6, it gets hotter but much less bright.

Question

Quizplus · Accepted Answer

As a protostar evolves from stage 4 to stage 6, gravitational contraction causes an increase in temperature, but the protostar is still surrounded by its dusty envelope, which absorbs and scatters much of the radiation it emits. Therefore, the protostar becomes hotter but also less visible and bright. During stage 4, the protostar is still accreting mass and its energy is primarily released as visible light. As it evolves to stage 6, the central temperature increases and the energy is primarily released as infrared radiation, which is less bright in the visible spectrum. Therefore, the protostar gets hotter but much less bright as it evolves to stage 6.

As a Protostar Evolves from Stage 4 to Stage 6