ELI5- Why are galaxies not shaped as Spheres?
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Imagine one of those coin-spinner cone things. The charity ones where you put a coin in, it spins round and round the vortex, then falls through the middle.
Now imagine you chuck in like 30 coins at random. Some are going clockwise (maybe 18), some anticlockwise (12). It’s likely that some of the coins going in opposite directions will collide. When this happens, they’ll pretty much fall in to the middle right away. But there are more clockwise coins. So if they all try and cancel out, you’ll be left with 6 going clockwise.
Galaxies are full of pockets of stuff. This stuff forms planets and stars and comets and asteroids etc. It’s going in all sorts of different directions at different speeds and distances. But if two things going on different directions or even at different angles collide, then they’ll sort of cancel each other out a bit. In reality, they’ll tend to go together in a direction somewhere between each of their directions. Eventually, stuff all cancels out until everything is going in a disk in the one direction. This is pretty much how spiral galaxies are formed. It’s also, on a smaller scale, why all the planets in the solar system go in roughly a disk (the ecliptic plane) in one direction.
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