system
Given the following post, respond as if you're commenting on Reddit:
human
When a star runs out of fuel and collapses, does it happen all at once or does is slowly “deflate?”
gpt
Yes and no. In the grand scheme of things, it is very fast. But it still takes such a long time that a person living on a planet around it would hardly notice what was going on.

From the point where the star begins expanding to the point where the core is left as a white or black dwarf, it can take a few billion years.

That is, except if the star goes nova. The explosion of a supernova can be as fast as 100 seconds in duration, effectively making it so if you see the explosion, the star is already gone.