Answer: Protostar Stage
Explanation: During the protostar stage, a cloud of gas and dust collapses under its own gravity, leading to the formation of a dense core. As the core continues to contract, gravitational potential energy is converted into thermal energy, resulting in an increase in temperature. This process causes the protostar to emit radiation as it gradually heats up. The energy released during gravitational contraction helps counterbalance the inward force of gravity, preventing further collapse. Eventually, once the core temperature reaches a critical point, nuclear fusion ignites, and the star enters the main sequence stage, where its energy is primarily generated through nuclear reactions in the stellar core.