Why don't galaxies obey gravity?

[BenAS]

@OnlyMe: It is an order of magnitude estimate, a factor 2 more or less doesn't matter.

Can we please keep 10^-20 effects of general relativity out of a [B]-level thread? It is beyond the scope, and it is utterly negligible anyway.

So I think what he's asking about (I've been thinking about it also, which is why I asked about the math. Thanks btw) is wether or not spacetime can "rotate" around a galaxy. This would be in addition to the frame dragging. I figure people smarter than me (Not a high bar) have considered this. It seems it could change the expected orbital velocity of stars.

 

[OnlyMe]

So I think what he's asking about (I've been thinking about it also, which is why I asked about the math. Thanks btw) is wether or not spacetime can "rotate" around a galaxy. This would be in addition to the frame dragging. I figure people smarter than me (Not a high bar) have considered this. It seems it could change the expected orbital velocity of stars.

mfb is right in pointing out that my question and discussion is beyond the scope of a B level thread. Perhaps even an A level discussion.