A moving dielectric medium acts as an effective gravitational field on ligh
t. One can use media with extremely low group velocities [Lene Vestergaard
Hau ct al., Nature (London) 397, 593(1999)] to create dielectric analogs of
astronomical effects on Earth. In particular, a vortex flow imprints a lon
g-ranging topological effect on incident light and can behave like an optic
al black hole.