Centaurus A is the nearest giant elliptical and one of the most informative: NGC 5128 wears its history openly, wrapped in stellar streams and shells from past accretion events (Malin et al. 1983), and ringed by a system of satellite dwarfs that turned out to be organized. Most of CenA's satellites lie in a narrow spatial plane, and line-of-sight velocities show the majority sharing one sense of motion, a coherently rotating satellite plane around a third host after the Milky Way and Andromeda (Muller et al. 2018).
The configuration doubles the standard model's satellite-plane problem. Dispersion-supported, mildly anisotropic satellite distributions are the ΛCDM expectation, and kinematically coherent planes like CenA's appear in well under one percent of comparable simulated halos (Libeskind et al. 2015; Pawlowski 2018). CenA adds its own aggravation: the satellite plane aligns with the larger-scale tidal debris structure, so the model needs two independent rare accidents, an improbable plane and an improbably aligned stream system, in the same host. And as the third confirmed co-rotating plane, CenA is the system that broke the Milky-Way-specific defenses: explanations invoking our Galaxy's unusual history cannot reach a giant elliptical thirteen million light-years away.
The standing made CenA pivotal in the satellite-plane debate, converting two local curiosities into an apparent rule. Ongoing distance and velocity measurements of the fainter CenA dwarfs keep refining the plane's membership and kinematic coherence.