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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$\begingroup$ In addition to the answer you can also look at 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). $\endgroup$– AlchimistaCommented Apr 5, 2018 at 10:54
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$\begingroup$ Also astronomy.stackexchange.com/questions/1145/… $\endgroup$– ProfRobCommented Apr 6, 2018 at 7:59
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1 Answer
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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.
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3$\begingroup$ 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. $\endgroup$– pelaCommented Apr 5, 2018 at 12:28
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$\begingroup$ This answer [physics.stackexchange.com/a/25954/181563] describes the gas interactions, and some exceptions [elliptical galaxies and parts of solar system]. $\endgroup$ Commented Apr 5, 2018 at 19:04