  We present SDSSJ092712.65+294344.0 as the best candidate to date for a
recoiling supermassive black hole (SMBH). SDSSJ0927+2943 shows an exceptional
optical emission-line spectrum with two sets of emission lines: one set of very
narrow emission lines, and a second set of broad Balmer and broad
high-ionization forbidden lines which are blueshifted by 2650 km\s relative to
the set of narrow emission lines. This observation is most naturally explained
if the SMBH was ejected from the core of the galaxy, carrying with it the
broad-line gas while leaving behind the bulk of the narrow-line gas. We show
that the observed properties of SDSSJ0927+2943 are consistent with predictions
and expectations from recent numerical relativity simulations which demonstrate
that SMBHs can receive kicks up to several thousand km\s due to anisotropic
emission of gravitational waves during the coalescence of a binary. Our
detection of a strong candidate for a rapidly recoiling SMBH implies that kicks
large enough to remove SMBHs completely from their host galaxies do occur, with
important implications for models of black hole and galaxy assembly at the
epoch of structure formation, and for recoil models.
