Final answer:
A protostar is not producing energy until it becomes a main sequence star.
Step-by-step explanation:
A protostar is not producing energy. Initially, a protostar remains fairly cool with a very large radius and a very low density. It is transparent to infrared radiation, and the heat generated by gravitational contraction can be radiated away freely into space. However, as the protostar continues to collapse and become denser, it eventually reaches a point where it becomes hot enough to sustain nuclear fusion, at which point it begins producing its own energy as a main sequence star.