  One of the most extraordinary manifestations of the coupling of the optical
field and matter is the emission of light by charged particles passing through
a dielectric medium: the Vavilov-Cherenkov effect. In this article, it is
theoretically predicted that a related phenomenon may be observed when neutral
fast polarizable particles travel near a metal surface supporting surface
plasmon polaritons. Rather dramatically, it is found that at some critical
velocity, even if the initial optical field is vanishingly small, the system
may become unstable and may start spontaneously emitting light such that in
some initial time window the optical field grows exponentially with time.
