Are galaxies spherical or flat?
For example, (I understand that up and down don’t really matter, so bear with me) if we look at a picture of the Milky Way Galaxy on a plane… If you want to move from one arm of the galaxy to the next, could you just move UP and out of the current arm and then over and DOWN to a different arm?
Secondary question for if the first one is correct, if you are able to move “up” and out of the arm, where are you? Is that interstellar space too?
Comments
Galaxies come in a bunch of different shapes, but spiral galaxies like the Milky Way are reasonably flat. The disc is about 1000 light years thick, and about 100,000 light years across. So, yes, if you traveled “up” perpendicular to the disc you’d exit the galaxy much quicker.
Elliptical galaxies on the other hand can be almost spherical.
So, to answer your question: they can be either one.
The Milky Way is disk shaped, so it has thickness, but it’s a long way from a sphere.
Galaxies vary in shape, but many are spiral shaped like ours.
The motion you described is possible, though it would take a looooong time to move “up” enough to be considered to be in intergalactic space.
Space is 3-dimensional regardless, so you can go in a straight line or go that circuitous route for no reason. There’s nothing special about “interstellar space” versus “intergalactic space” except that intergalactic space is an even more complete vacuum (but still not perfectly so). The shape of the galaxy (and they come in a vast array of shapes) has no bearing on travel – it’s all still almost completely empty so the shortest path is always going to be the straight line (ignoring complexities like relative velocities of your start and end locations) – you don’t need to go “outside” to avoid anything.