Question: Why and how are the stars in the galaxy growing bigger?

Miriam Hogg answered on 8 Nov 2018:

The stars in the galaxy aren’t growing bigger. Most stars are actually smaller than our Sun. Stars form from a cloud of gas and once they form they stay the same mass most of their lives, in fact they lose small amounts of mass over their life through wind. When they run out of fuel they have reached the end of their lifetime and expand into a giant star and throw off their outer layers, leaving behind the hot core which we call a white dwarf.
This white dwarf slowly cools over time and will eventually be too cold to be visible which we call a black dwarf, although we don’t think this has happened yet as the universe isn’t old enough for a white dwarf to have cooled that much.