STARS EXPAND BEFORE THEY DIE..

The main reason why stars expand as they age is because a star is always getting hotter and hotter as the helium ash from hydrogen fusion slowly builds up at the core and is compressed under its own weight. This makes the core more resistant to further fusion, which means less energy is produced to counteract gravity. As a result, the core starts to collapse under its own weight, which increases the pressure and temperature even more.

While the core collapses, the outer layers of material in the star expand outward. This is because the increased temperature in the core makes the star more luminous, which means it radiates more energy into space. This energy pushes on the outer layers of the star, making them swell up like a balloon. The star also loses mass through stellar winds, which are streams of gas that escape from the surface of the star. This makes the star even lighter and easier to inflate.

Depending on the mass of the star, this process can go on for millions or billions of years, until the star runs out of fuel or explodes in a spectacular supernova. The final fate of the star depends on how much mass it has left after shedding its outer layers. It can become a white dwarf, a neutron star, or a black hole. But that's another story for another time.