Red Giants and White Dwarfs

What happens when a Main sequence star runs out of hydrogen in its core? Let’s explore that.

When all the hydrogen in a star is used up, the inward force of gravity becomes prominent compared to the outward force created by fusion.

This squeezes the core, and its temperature and pressure increase so much that its helium begins to fuse into carbon, which also releases energy.

At the same time, hydrogen fusion begins in the star’s outer layers, causing them to expand.

This creates a larger, cooler, red-colored star called a red giant.

As time passes, the red giant eventually exhausts all its helium, and fusion stops. What happens next to the star depends on its mass.

If a star has a mass less than about 8 times the mass of the Sun, it loses its outer layers, leaving behind its core.

The core collapses into a small, hot, glowing object about the size of Earth called a white dwarf.