  We investigate the stability of vortices in two-dimensional Bose--Einstein
condensates. In analogy with rotating spacetimes and with a careful account of
boundary conditions, we show that the dynamical instability of multiply
quantized vortices in trapped condensates persists in untrapped, spatially
homogeneous geometries and has an ergoregion nature with some modification due
to the peculiar dispersion of Bogoliubov sound. Our results open new
perspectives to the physics of vortices in trapped condensates, where multiply
quantized vortices can be stabilized by interference effects and singly charged
vortices can become unstable in suitably designed trap potentials. We show how
superradiant scattering can be observed also in the short-time dynamics of
dynamically unstable systems, providing an alternative point of view on
dynamical (in)stability phenomena in spatially finite systems.
