  Satellite galaxies are tidally disrupted as they orbit the Milky Way. If dark
matter (DM) experiences a stronger self-attraction than baryons, stars will
preferentially gain rather than lose energy during tidal disruption leading to
an enhancement in the trailing compared to the leading tidal stream. The Sgr
dwarf galaxy is seen to have roughly equal streams, challenging models in which
DM and baryons accelerate differently by more than 10%. Future observations and
a better understanding of DM distribution should allow detection of equivalence
violation at the percent level.
