  Analogue gravity studies the physics of curved spacetime in laboratory
experiments, where the propagation of elementary excitations in inhomogeneous
flows is mapped to those of scalar fields in a curved spacetime metric. While
most analogue gravity experiments are performed in 1+1 dimensions (one spatial
plus time) and thus can only mimic only 1+1D spacetime, we present a 2+1D
photon (room temperature) superfluid where the geometry of a rotating acoustic
black hole can be realized in 2+1D dimensions. By measuring the local flow
velocity and speed of waves in the superfluid, we identify a 2D region
surrounded by an ergo sphere and a spatially separated event horizon. This
provides the first direct experimental evidence of an ergosphere and horizon in
any system, and the possibility in the future to study the analogue of Penrose
superradiance from rotating black holes with quantised angular momentum and
modified dispersion relations.
