Dwarf satellite galaxies undergo strong tidal forces produced by the main galaxy potential .
These forces disturb the satellite , producing asymmetries in its stellar distribution , tidal tail formation , and modifications of the velocity dispersions profiles .
Most of these features are observed in the Ursa Minor ( UMi ) dwarf spheroidal galaxy , which is one of the closest satellites of the Milky Way .
These features show that UMi is been tidally disrupted and probably not in virial equilibrium .
The high velocity dispersion of UMi could also be a reflection of this tidal disruption and not the signature of the large dark matter content that would be deduced if virial equilibrium is assumed .
In order to avoid the uncertainty produced when virial equilibrium is assumed in systems in strong tidal fields , we present a new method of calculating the mass-to-luminosity ratio of disrupted dwarf galaxies .
This method is based on numerical simulations and only takes into account the shape of the dwarf density profile and the tidal tail brightness , but does not depend on the kinematics of the dwarf .
Applying this method to UMi , we obtain a mass-to-luminosity relation of 12 , which is lower than the value obtained assuming virial equilibrium ( M / L = 60 ) .
In addition , if UMi has a large dark-matter content , it will be impossible to reproduce a tidal tail as luminous as the one observed .