system
Given the following post, respond as if you're commenting on Reddit:
human
How can a galaxy by so big that it does not fit into our current models of physics?

Pardon my stupidity if this question is not actually legitimate because I saw the premise on a reddit thread.
gpt
It's a pretty huge exaggeration. Big galaxies form through a build-up of smaller galaxies over time: we start with a lot of little galaxies that merge with each other into bigger and bigger galaxies. We can do some math to work out the masses of these original galaxies, and how rapidly they merge with each other, and from that you can get an estimate of how big a typical galaxy should be at whatever time in whatever environment we've observing it at - environment matters because some galaxies are in denser areas than others. But applying this to one particular galaxy is pretty iffy, because you really can't make that detailed a prediction about the number and mass of galaxies that this big galaxy came from. You might see a galaxy that seems unusually large, but there's no hard rule that stops you from getting very large galaxies. We may not know the particular events that caused this galaxy to become so massive - and this is the "mystery" - but that's very different to saying that this galaxy breaks physics somehow.