  We study a coupled dynamics of a network and a particle system. Particles of
density $\rho$ diffuse freely along edges, each of which is rewired at a rate
given by a decreasing function of particle flux. We find that the coupled
dynamics leads to an instability toward the formation of hubs and that there is
a dynamic phase transition at a threshold particle density $\rho_c$. In the low
density phase, the network evolves into a star-shaped one with the maximum
degree growing linearly in time. In the high density phase, the network
exhibits a fat-tailed degree distribution and an interesting dynamic scaling
behavior. We present an analytic theory explaining mechanism for the
instability and a scaling theory for the dynamic scaling behavior.
