Eli5: why are galaxies flat and not sphere?
In: Planetary Science
Because orbits slowly attract each other.
The older the galaxy, the flatter it will become.
Picture 2 orbits that dont share same plane, and look at the gravitational forces when the planets are at shortest distance. You will see they mildly pull each other into their own orbit.
Since there arent any other forces invoved they will slowly get into the same plane
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