On the thermal description of the BTZ black holes

We investigate the limitations on the thermal description of three-dimensional BTZ black holes. We derive on physical grounds three basic mass scales that are relevant to characterize these limitations. The Planck mass in 2+1 dimensions indicates the limits where the black hole can emit Hawking's radiation. We show that the back reaction is meaningless for spinless BTZ black hole. For stationary BTZ black holes the nearly extreme case is analyzed showing that may occur a breakdown of its description as a thermal object.