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I know this is a very dumb question, but, to maintain a galaxy as a bounded system, the total energy and the total angular momentum of every particle component of the galaxy (suppose made of gas and dust) should be bounded from above? How could one determine this bound?

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  • $\begingroup$ what do you mean by bounded from above? Are you asking about conservation of momentum, or how the galaxy maintains its rotation? $\endgroup$ – Miniucnchew Aug 21 '16 at 16:24
  • $\begingroup$ I mean that if the energy of a particle exceeds some characteristic energy or angular momentum, it could scape from the well created by the gravitational field. $\endgroup$ – user115376 Aug 21 '16 at 16:46
  • $\begingroup$ What have you done to look for an answer already? Have you studied the wikipedia article on Orbital Mechanics? $\endgroup$ – sammy gerbil Aug 23 '16 at 10:20
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According to what I interpret The problem is galaxies are "finite" systems, there should be a cutoff radial edge or optical radius above which there are no more stars and there's a gas depletion. This radius depend of course of the form of the potential and the energy and angular momentum of the particles, otherwise they can scape from the gravitational field and the galaxy vanishes.

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