system
Given the following post, respond as if you're commenting on Reddit:
human
If planets orbit a star, and galaxies orbit a black hole (or something in the center), are clusters of galaxies orbiting anything?  Second question inside

Yeah, I know, this is probably a stupid question, and I should have posted it in the tell-me-like-I'm-five subreddit, but it seems to me that there shouldn't be any difference between the movements of planets and galaxies and clusters of galaxies. If the tendency is for bodies to orbit a central point (regardless of what it is), then what makes groups of galaxies different?  I am wondering why the pattern wouldn't apply to the entire universe?  What makes it stop happening?

Question 2: Could Earth have been part of another galaxy originally?  Would science be able to determine if we've always been here?  If we were part of Sag DEG at some point, would that have any significance when the MW became our home?

Thank you in advance for your indulgence.
gpt
While planets are gravitationally bound to their host stars, galaxies are a bit different.  Galaxies have flat rotation curves, meaning, stuff on the outer edges of the galaxy aren't moving much more slowly than stuff closer to the center-- galaxies are usually home to dark matter halos.

In a galaxy cluster, hot gas called ICM (intracluster medium) and way more dark matter inhabits the space through which these galaxies interact.

This schematic breaks down when the influence of dark matter is small compared to the driving force of the universe's expansion: dark energy.  Far enough apart, galaxy clusters will not be bound to each other, but helplessly pulled in space as it expands in all directions.