What energy source powers a protostar during its phase of contraction before fusion begins?

Answer

Heat released by gravitational contraction (Kelvin-Helmholtz mechanism)

During the protostar phase, the energy illuminating the object is derived entirely from the heat generated as gravitational potential energy is converted during the ongoing shrinkage, known as the Kelvin-Helmholtz mechanism.

What energy source powers a protostar during its phase of contraction before fusion begins?

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