<p>Flatness is caused by conservation of angular momentum. As solar system/galaxy collapses under its own gravity, its velocity increases to conserve the angular momentum. This high velocity leads to formation of disc shaped structure. The similar manner in which piece of dough becomes flat when it is rotated. </p>

CC BY-SA 3.0
2018-04-05T12:28:41.860Z
Conservation of angular momentum isn't enough, because then dark matter structures would be flat too, whereas they are in fact much more spherical (though still elliptical). Your answer neglects a very important ingredient, namely the dissipation of energy by the collisional gas.
pela
CC BY-SA 3.0
2018-04-05T19:04:09.577Z
This answer [https://physics.stackexchange.com/a/25954/181563] describes the gas interactions, and some exceptions [elliptical galaxies and parts of solar system].
Bit Chaser
CC BY-SA 3.0
2018-04-05T05:40:30.690Z
2018-04-05T05:40:30.690Z
Gauti
<p>If we look around the cosmos, we will see most of the systems are just flat disks. Either it is solar system, galaxies, or the rings of Saturn. What is the matter, does it depend on how they were formed, or anything else?</p>

<p><a href="https://i.sstatic.net/H4sig.jpg" rel="nofollow noreferrer"><img src="https://i.sstatic.net/H4sig.jpg" alt="enter image description here"></a></p>

CC BY-SA 3.0
2018-04-05T10:54:26.570Z
In addition to the answer you can also look at https://astronomy.stackexchange.com/questions/24621/oort-cloud-shape  as I got an answer emphasising intrrecation (electromagnetic like in the dough, gravitational, or simply by collisions).
Alchimista
CC BY-SA 3.0
2018-04-06T07:59:40.200Z
Also https://astronomy.stackexchange.com/questions/1145/why-are-galaxies-disk-shaped
ProfRob
<astrophysics><cosmology><fundamental-astronomy>
Flatness of celestial systems like galaxies and Solar System
Abhishek Thawait
# Flatness of celestial systems like galaxies and Solar System

(Asked by: username_0 on 2018-04-05)

If we look around the cosmos, we will see most of the systems are just flat disks. Either it is solar system, galaxies, or the rings of Saturn. What is the matter, does it depend on how they were formed, or anything else?

[![enter image description here](https://i.sstatic.net/H4sig.jpg)](https://i.sstatic.net/H4sig.jpg)

**Tags:** astrophysics, cosmology, fundamental-astronomy
> **Comments:**
> **username_1**: In addition to the answer you can also look at https://astronomy.stackexchange.com/questions/24621/oort-cloud-shape  as I got an answer emphasising intrrecation (electromagnetic like in the dough, gravitational, or simply by collisions).  
> **username_2**: Also https://astronomy.stackexchange.com/questions/1145/why-are-galaxies-disk-shaped  

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## 1 answers

### Answer by username_3 on 2018-04-05. Score: 0 | Accepted answer

Flatness is caused by conservation of angular momentum. As solar system/galaxy collapses under its own gravity, its velocity increases to conserve the angular momentum. This high velocity leads to formation of disc shaped structure. The similar manner in which piece of dough becomes flat when it is rotated.

> **Comments:**
> **username_4**: Conservation of angular momentum isn't enough, because then dark matter structures would be flat too, whereas they are in fact much more spherical (though still elliptical). Your answer neglects a very important ingredient, namely the dissipation of energy by the collisional gas.  
> **username_5**: This answer [https://physics.stackexchange.com/a/25954/181563] describes the gas interactions, and some exceptions [elliptical galaxies and parts of solar system].  

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