  Spiral waves in active media react to small perturbations as particle-like
objects. Here we apply the asymptotic theory to the interaction of spiral waves
with a localized inhomogeneity, which leads to a novel prediction: drift of the
spiral rotation centre along circular orbits around the inhomogeneity. The
stationary orbits have alternating stability and fixed radii, determined by the
properties of the bulk medium and the type of inhomogeneity, while the drift
speed along an orbit depends on the strength of the inhomogeneity. Direct
simulations confirm the validity and robustness of the theoretical predictions
and show that these unexpected effects should be observable in experiment.
