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Deriving bar instability mode- formal definition of instability?

  1. Mar 15, 2012 #1
    I am doing an undergraduate project on bars and I am trying to derive the bar instability mode given by Mo et al. It says "whether or not a disk is globally stable depends on the global properties of the disk... it is not possible to write down a universal dispersion relation or stability criterion."

    I am wondering what the formal, physical definition of an instability is. I know it has something to do with potential energies. Could someone provide a general definition of an instability? Links to sources would be appreciate, as I might want to cite a definition.
  2. jcsd
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