%0 Journal Article %T Core-halo instability in dynamical systems %A Seth Lloyd %J Physics %D 2013 %I arXiv %X This paper proves an instability theorem for dynamical systems. As one adds interactions between subystems in a complex system, structured or random, a threshold of connectivity is reached beyond which the overall dynamics inevitably goes unstable. The threshold occurs at the point at which flows and interactions between subsystems (`surface' effects) overwhelm internal stabilizing dynamics (`volume' effects). The theorem is used to identify instability thresholds in systems that possess a core-halo or core-periphery structure, including the gravo-thermal catastrophe -- i.e., star collapse and explosion -- and the interbank payment network. In the core-halo model, the same dynamical instability underlies both gravitational and financial collapse. %U http://arxiv.org/abs/1302.3199v2