  A ring system consisting of two dense narrow rings has been discovered around
Centaur Chariklo. The existence of these rings around a small object poses
various questions, such as their origin, stability, and lifetime. In order to
understand the nature of Chariklo's rings, we perform global $N$-body
simulations of the self-gravitating collisional particle rings for the first
time. We find that Chariklo should be denser than the ring material to avoid
the rapid diffusion of the rings. If Chariklo is denser than the ring material,
fine spiral structures called self-gravity wakes occur in the inner ring. These
wakes accelerate the viscous spreading of the ring significantly and they
typically occur on timescales of about $100\,\mathrm{years}$ for m-sized ring
particles, which is considerably shorter than the timescales suggested in
previous studies. The existence of these narrow rings implies smaller ring
particles or the existence of shepherding satellites.
