Vacuum has friction from an effect similar to the casimir effect

The phenomenon of vacuum friction for spinning objects is somewhat different than for the static parallel plates: the accelerating charges in a spinning conductive object interact with the vacuum fluctuations and can emit photons.

A quick scan of the paper (pdf) indicates that the thermally radiated photons have a different net angular momentum than the ones absorbed from the reservoir, i.e. the effect is that the emitted light has a net polarization which carries off the angular momentum as the particle slows down.