  A moving dielectric medium acts as an effective gravitational field on light.
One can use media with extremely low group velocities [Lene Vestergaard Hau et
al., Nature 397, 594 (1999)] to create dielectric analogs of astronomical
effects on Earth. In particular, a vortex flow imprints a long-ranging
topological effect on incident light and can behave like an optical black hole.
