system
Given the following post, respond as if you're commenting on Reddit:
human
Do galaxies die? How many years would that take? Could some of the most distant galaxies we've observed be long gone today?
gpt
Well, it depends on how you define "death".  Galaxies collide and merge with each other, so lots of the galaxies we see that are billion of years old may not be there anymore, because they have merged with nearby galaxies, and thus today they would look totally different.  Their constituent stars would still be there, however, more or less, (minus any that have died since), since galactic collisions are usually pretty harmless to the stars within the galaxies, since the chances of stars colliding during such an event is extremely low due to the sheer amount of empty space in between stars in galaxies.

All things being equal galaxies will eventually "burn out" though, as all their stars run out of fuel and die, and slowly all the lights will eventually dim for every galaxy in the Universe.  But that process takes trillions of years because even after a star runs out of fuel, it turns into a white dwarf which still glows fairly brightly for a VERY long time.