In addition to lines originating in a soft phase at \sim 0.8 keV and to cold molecular clouds , the X-ray spectra from the Galactic center region also exhibit properties similar to those of a diffuse , thin , very hot plasma at 8 keV on a scale of hundreds of parsecs .
This phase is surprising for more than one reason .
First , such a hot plasma should not be bound to the Galactic plane and the power needed to sustain the escaping matter would be higher then any known source .
Second , there is no known mechanism able to heat the plasma to more than a few keV .
Recently we have suggested that , hydrogen having escaped , the hot plasma could be a helium plasma , heavy enough to be gravitationally confined .
In this case , the required power is much more reasonable .
We present here a possible heating mechanism which taps the gravitational energy of the molecular clouds .
We note that the 8 keV plasma is highly viscous and we show how viscous friction of molecular clouds flowing within the hot phase can dissipate energy in the gas and heat it .
We detail the MHD wake of a spherical cloud by considering the different MHD waves the cloud can excite .
We find that most of the energy is dissipated by the damping of Alfvénic perturbations in two possible manners , namely by non-linear effects and by a large scale curvature of the field lines .
We find that the total dissipation rate depends on the field strength .
For fields B \lesssim 200 \mu G both mechanisms produce power comparable to or higher than the radiative losses ; for strong fields B \gtrsim  1 mG , only the curvature damping can balance the X-ray emission and requires a radius of curvature R _ { \mathrm { c } } \lesssim 100 pc ; whereas for intermediate fields , the total dissipation is more than one order of magnitude smaller , requiring a higher accretion rate .
We note that the plasma parameters may be optimal to make the dissipation most efficient , suggesting a self-regulation mechanism .
The loss of kinetic and gravitational energy also causes accretion of the clouds and may have significant action on the gas dynamics in this region between the large scale , bar dominated flow and the central accretion to the massive black hole .