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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?

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peterh
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Abhishek Thawait
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  • 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 Apr 05 '18 at 10:54
  • Also https://astronomy.stackexchange.com/questions/1145/why-are-galaxies-disk-shaped – ProfRob Apr 06 '18 at 07:59

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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.

Gauti
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    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 Apr 05 '18 at 12:28
  • 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 Apr 05 '18 at 19:04