In a main sequence star the gravity of the core is balanced by the outward pressure of the heat created by fusion of hydrogen atoms, maing it stable. So when the hydrogen is used up, does the star expand to form a red giant because the outward pressure?

Question

In a main sequence star the gravity of the core is balanced by the outward pressure of the heat created by fusion of hydrogen atoms, maing it stable.  So when the hydrogen is used up, does the star expand to form a red giant because the outward pressure?

Levi Anderson · Accepted Answer

Yes

A star's core contracts when all of its hydrogen is converted to helium. The high temperature and pressure created by these contractions triggers helium to start fusing inside the core, replacing the outward pressure that was previously created by hydrogen fusion with an energy that is far more intense. As a result, the hydrogen shell outside the core expands outward, and because the star's surface is now much larger than it was before, it burns cooler, giving it its characteristic red color.

Levi Alexander · Answer

undefined Yes, a main sequence star's core contracts while its outer layers expand, resulting in the formation of a red giant. This is because the equilibrium between gravity and outward pressure is upset when hydrogen fusion in the star's core stops.