system
Given the following post, respond as if you're commenting on Reddit:
human
Galaxies are hundreds of thousands of lightyears in diameter, and gravity only travels with the speed of light. Does this not distort the shape of them?

Or is this the reason for that galaxies have "arms"?
gpt
The Sun's orbit around the galaxy needs about 250 million years and the overall mass has been there for billions of years.

Tens of thousands of years are simply negligible on the timescale of galaxies.