On their massive scale you’d think that several would have opposing arms different lengths due to the way suns and solar systems end up forming. Most of the imagery I see shows almost all galaxies symmetrical. Just curious.
The fact they spin and the bits interact gravitationally makes them symmetric. There are almost certainly some asymmetric galaxies as we know galaxies collide and they will be asymmetric for a bit afterwards, but the spinning and fiction of gravity will make them symmetric again fairly quickly on galactic time scales.
Your question made me realize I had never thought about this at all so I spent some time searching. If I am understanding this article correctly it essentially boils down to the factors that would cause rotational symmetry at a smaller scale ie spinning sand on a plate apply at the galaxy scale as well.
Id guess if the arm gets too long, gravity won’t be strong enough anymore so the stars there will sort of just drift off
