What signals the transition out of the main sequence phase for a star?

Answer

The disruption of the long-held hydrostatic balance

The transition out of the main sequence is marked by the disruption of the hydrostatic balance, which occurs when the core hydrogen fuel is exhausted and fusion ceases in the center.

What signals the transition out of the main sequence phase for a star?

#Videos

Why Is the Main Sequence a Star's Longest Stable Phase? - YouTube

stabilitystarstellar evolutionmain-sequenceastrophysics