Question

what must occur for a protostar to officially become a star?
○ fission of hydrogen into helium
○ fusion of hydrogen into helium
○ hydrostatic equilibrium
○ collapse of the core

Explanation:

A protostar becomes a star when nuclear fusion begins. Fusion of hydrogen into helium releases energy, countering gravitational collapse. Hydrostatic equilibrium (balance between gravity and pressure) is maintained post - fusion. Fission (splitting atoms) is not stellar process. Core collapse is part of protostar formation, not star - becoming event.

Answer:

fusion of hydrogen into helium