What delicate equilibrium must a star achieve to reside on the main sequence?

Answer

Hydrostatic balance

For any object, including a star, to maintain a stable structure over vast timescales, it must achieve a condition of hydrostatic balance. This concept describes a perfect, dynamic standoff between two opposing forces acting upon the star's mass. On one side is the relentless, inward force exerted by the star's immense self-gravity, which constantly tries to crush the star inward. Opposing this is the outward pressure generated by the massive amount of energy released from the nuclear fusion reactions occurring deep within the star's core. When these two forces—inward gravity and outward fusion pressure—are perfectly matched, the star ceases contraction or expansion and settles into the stable configuration known as the main sequence.

What delicate equilibrium must a star achieve to reside on the main sequence?

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