Reading about the formation of planetary disks, one of the major problems, it seems like, is the evacuation of angular momentum. Aparently planets can't form with the amount o angular momentum the system has in its early stages. I think I understand where that excess comes from, the collapse of the nebula onto itself and provoking a spin. Then there are many hypothesis on how it's evacuated, which are mostly pretty logical.

Now my question, as a beginner in the study of physics, is this: Why does the angular momentum even need to be evacuated? If the angular momentum is too big, why can't planets still form? Does this have something to do with too much kinetic energy in the system? Thank you!

  • $\begingroup$ I suppose this is related with the formation of the system itself (the mass has to flow towards the inner region). Could you please link a reference where you read about the angular momentum condition? $\endgroup$
    – Py-ser
    Mar 8, 2015 at 10:50
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    $\begingroup$ Hmmm... I'm not expert on planet formation, but a basic issue will be accumulating enough material to make a planet in the first place. For a specified amount of angular momentum, material must orbit at a certain distance from the central object. So, at first, too much material is too far away, and to get closer it has to lose angular momentum. $\endgroup$
    – Warrick
    Mar 11, 2015 at 7:10
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    $\begingroup$ Also on Physics. $\endgroup$
    – HDE 226868
    Mar 11, 2015 at 22:16
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    $\begingroup$ And a good answer on Physics SE too. $\endgroup$
    – ProfRob
    Dec 29, 2016 at 13:35
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    $\begingroup$ @Warrick Please convert to an answer. $\endgroup$
    – called2voyage
    Feb 21, 2018 at 16:52


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