When does a star become a main-sequence star?
A)when the protostar assembles from a molecular cloud
B)the instant when hydrogen fusion first begins in the star's core
C)when the rate of hydrogen fusion within the star's core is high enough to maintain gravitational equilibrium
D)when a star becomes luminous enough to emit thermal radiation
E)when hydrogen fusion is occurring throughout a star's interior

Question

Quizplus · Accepted Answer

A star becomes a main-sequence star when the rate of hydrogen fusion within its core is sufficient to maintain gravitational equilibrium, balancing the inward pull of gravity with the outward pressure from fusion.

When Does a Star Become a Main-Sequence Star