Question

circle of life

1. when does a star become a main-sequence star?

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Explanation:

To determine when a star becomes a main - sequence star, we refer to stellar evolution concepts. A star enters the main - sequence stage when the gravitational contraction of the protostar leads to a core temperature and pressure high enough for hydrogen fusion (specifically the proton - proton chain or CNO cycle) to start and balance the inward gravitational force with the outward thermal and radiation pressure. In other words, when hydrogen fusion begins in its core and hydrostatic equilibrium is achieved (the outward pressure from fusion balances the inward pull of gravity), the star is a main - sequence star.

Answer:

A star becomes a main - sequence star when hydrogen fusion starts in its core and hydrostatic equilibrium (outward pressure from fusion balances inward gravitational pull) is achieved.