  The Milky Way and Andromeda galaxy are each surrounded by a thin plane of
satellite galaxies that may be corotating. Cosmological simulations predict
that most satellite galaxy systems are close to isotropic with random motions,
so those two well-studied systems are often interpreted as rare statistical
outliers. We test this assumption using the kinematics of satellite galaxies
around the Centaurus A galaxy. Our statistical analysis reveals evidence for
corotation in a narrow plane: of the 16 Centaurus A's satellites with kinematic
data, 14 follow a coherent velocity pattern aligned with the long axis of their
spatial distribution. In standard cosmology simulations, < 0.5% of Centaurus
A-like systems show such behavior. Corotating satellite systems may be common
in the Universe, challenging small-scale structure formation in the prevailing
cosmological paradigm.
