  Dense enough compact objects were recently shown to lead to an exponentially
fast increase of the vacuum energy density for some free scalar fields properly
coupled to the spacetime curvature as a consequence of a tachyonic-like
instability. Once the effect is triggered, the star energy density would be
overwhelmed by the vacuum energy density in a few milliseconds. This demands
that eventually geometry and field evolve to a new configuration to bring the
vacuum back to a stationary regime. Here, we show that the vacuum fluctuations
built up during the unstable epoch lead to particle creation in the final
stationary state when the tachyonic instability ceases. The amount of created
particles depends mostly on the duration of the unstable epoch and final
stationary configuration, which are open issues at this point. We emphasize
that the particle creation coming from the tachyonic instability will occur
even in the adiabatic limit, where the spacetime geometry changes arbitrarily
slowly, and therefore is quite distinct from the usual particle creation due to
the change in the background geometry.
