Eli5: why are galaxies flat and not sphere?
In: Planetary Science
you start out with a bunch of stuff orbiting in random directions in a sphere. Over time, random stuff going “up” crashes into random stuff going “sideways” or even “down”. Over time this deorbits everything moving the wrong direction into the galactic core, or it changes its orbit to a mostly flat plane with everything orbiting in the same direction.
Same principal as why the solar system is a flat disk
There is an excellent visualization of this in https://www.youtube.com/watch?v=MTY1Kje0yLg&t=190s
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