Why do galaxies look like they spread out in a single plane (ie, why do they look more like frisbees than spheres)?
In: Physics
That is not strictly correct. Your question, I mean. Plz check this:
[https://i.ytimg.com/vi/78malg3gqmE/maxresdefault.jpg](https://i.ytimg.com/vi/78malg3gqmE/maxresdefault.jpg)
[https://briankoberlein.com/blog/how-galaxies-die/galaxygraph.jpg](https://briankoberlein.com/blog/how-galaxies-die/galaxygraph.jpg)
[https://www.nationalgeographic.com/science/article/galaxies](https://www.nationalgeographic.com/science/article/galaxies)
[https://www.reddit.com/r/askscience/comments/gv6rj9/why_galaxies_are_flat_why_there_are_no_spherical/fsnrgku?utm_source=share&utm_medium=web2x&context=3](https://www.reddit.com/r/askscience/comments/gv6rj9/why_galaxies_are_flat_why_there_are_no_spherical/fsnrgku?utm_source=share&utm_medium=web2x&context=3)
In short:
1) galaxies do not start neither end as a disk or a ball – so when we look into far, far away – we see many ages of these galaxies.
2) Even then – not all galaxies are flat, only the majority.
3) And even then – it is only the visible part that is flat, all together they should be closer to the ball, then a pancake.
The reason many galaxies are flat is because of the conservation of angular momentum. When objects revolve around the center of gravity, they have angular momentum. Given enough time, a rotating body of stars may flatten into an overall disk shape.
This band of stars can be seen with the naked eye in places with dark night skies. That band comes from seeing the disk of stars that forms the Milky Way from inside the disk, and tells us that our galaxy is basically flat.
[https://www.reddit.com/r/explainlikeimfive/comments/9wnvfb/eli5_why_are_galaxies_flat_i_would_imagine_that_a/](https://www.reddit.com/r/explainlikeimfive/comments/9wnvfb/eli5_why_are_galaxies_flat_i_would_imagine_that_a/) – 2 years ago
[https://www.reddit.com/r/space/comments/2zd52d/why_are_galaxies_flat/](https://www.reddit.com/r/space/comments/2zd52d/why_are_galaxies_flat/) – 6 years ago
[https://www.reddit.com/r/askscience/comments/gv6rj9/why_galaxies_are_flat_why_there_are_no_spherical/](https://www.reddit.com/r/askscience/comments/gv6rj9/why_galaxies_are_flat_why_there_are_no_spherical/) – last year
[https://www.reddit.com/r/askscience/comments/awaqky/why_are_galaxies_a_flat_disk_and_not_a_sphere/](https://www.reddit.com/r/askscience/comments/awaqky/why_are_galaxies_a_flat_disk_and_not_a_sphere/) – 2 years ago
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Elliptical galaxies (spherical/ovoidal) types are more abundant than disk galaxies. IIRC it’s due to the way galaxy merging happens while the other is due to conservation of angular momentum and central forces.
You ever see someone throwing and rotating pizza dough in the air and as it rotates it flattens out mid air?
Galaxies are just giant pizza doughs.
When you spin around in a circle quickly, and feel your arms being pulled outward, do they get pulled straight outward when they’re relaxed, or do they fly all over the place?
Something I haven’t seen explained yet which is crucial to understanding this: Nothing can spin on more than one axis at a time.
Say you have a ball floating in the air before you. You spin the side facing you downward, now the axis of rotation is a horizontal line in front of you. Try to add a spin to the right at the same speed, and you don’t have two different spins; you have one spin diagonally downward and to the right.
Thus, spin forces *cannot* create a sphere, they can only create a disc shape.
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