Before fusion dominates, what mechanism supplies the energy output of a contracting protostar?

Answer

Gravitational contraction (Kelvin-Helmholtz mechanism)

Until the core reaches the threshold for stable fusion, the object's energy generation is solely attributed to the heat released as gravity continues to compress the core structure.

Before fusion dominates, what mechanism supplies the energy output of a contracting protostar?
protostarstellar evolutionstar formationastrophysicscollapse