  Long, cylindrical metal nanowires have recently been observed to form and be
stable for seconds at a time at room temperature. Their stability and
structural dynamics is well described by a continuum model, the nanoscale
free-electron model, which predicts cylinders in certain intervals of radius to
be linearly unstable. In this paper, I study how a small, localized
perturbation of such an unstable wire grows exponentially and propagates along
the wire with a well-defined front. The front is found to be pulled, and forms
a coherent pattern behind it. It is well described by a linear marginal
stability analysis of front propagation into an unstable state. In some cases,
nonlinearities of the wire dynamics are found to trigger an invasive mode that
pushes the front. Experimental procedures that could lead to the observation of
this phenomenon are suggested.
