When most main sequence stars exhaust their hydrogen supply, they become giants. Yet on the diagram, there are not many stars between the main sequence and the giants. What would explain this fact?

Main sequence stars change into giant star by exhausting their hydrogen supply.

Explanation:

This fact explain that main sequence stars change into giant star by exhausting their hydrogen supply. A main sequence star burns due to the presence of hydrogen in its core, because of this burning the main sequence reaching the end of its life cycle. Then the pressure of fusion reaction provides an outward thrust that expands the star many times larger than its original size, that leads to the formation of a red giant.

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