What occurrence defines the end of the protostar phase of a star's life and the start of the main-sequence phase?
A) Convection begins in its interior.
B) The star stops accreting mass from the interstellar cloud.
C) The star begins to expand to become a red supergiant.
D) The nuclear reactions in its core allow it to gain hydrostatic equilibrium.

Question

Quizplus · Accepted Answer

The protostar phase ends when the nuclear reactions in its core allow it to gain hydrostatic equilibrium, which is the balance between the outward force of gas pressure and the inward force of gravity. This marks the beginning of the main-sequence phase, where the star will continue to burn hydrogen in its core for a significant portion of its lifetime.

What Occurrence Defines the End of the Protostar Phase of a Star's