[hosepipe]

[... In a galaxy everything is simply rotating in a peculiar gravity field and is not being driven either inward or outward so that specious forces would not operate. ..]

Sounds logical except for the fact literally no one knows what gravity is..
Probably because some think gravity is multi dimensional.. and probably is..
I prefer the "light" energy/matter, "dark" energy/matter mental figment(s) as a metaphorical answer..

[RightWhale]

Then what is your metaphorical coriolis effect?