currently I am curious about proto-planetary nebulae. At first I was curious about how planets spin but I read in a couple of articles that they got their spin from when they were in a proto-planetary nebula and the momentum stayed because of conservation of momentum. But now a new question arises, where exactly do proto-planetary nebula's get their momentum from? I've searched this up on the internet but I haven't really gotten a clear response.

  • $\begingroup$ Planets formed in protoplanetary disks, not planetary nebulae (which form after a star dies). $\endgroup$ – HDE 226868 Oct 2 '15 at 22:02
  • $\begingroup$ Protplanetary nebulae should really be called proto-planetary nebulae (note the hyphen) because they form just before planetary nebulae (not planets) - which have nothing to do with planets! $\endgroup$ – HDE 226868 Oct 4 '15 at 23:49

The angular momentum comes from the chaotic/turbulent collapse of the parent molecular cloud. The collapse is turbulent because the initial conditions in the parent cloud are not spherically symmetric. This leave the proto-stellar clumps with non-zero angular momentum even if the parent cloud started with zero angular momentum. The sum of the angular momenta of all the material of the original cloud after fragmentation is still that of the cloud before fragmentation.

Some other/external triggering events for molecular cloud collapse can impart non-zero angular momentum to the cloud as a whole, but this is not necessary for the the individual fragments to end up with angular momentum.


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