Stellar streams as gravitational experiments I. The case of Sagittarius
  Tidal streams of disrupting dwarf galaxies orbiting around their host galaxy
offer a unique way to constrain the shape of galactic gravitational potentials.
Such streams can be used as leaning tower gravitational experiments on galactic
scales. The most well motivated modification of gravity proposed as an
alternative to dark matter on galactic scales is Milgromian dynamics (MOND),
and we present here the first ever N-body simulations of the dynamical
evolution of the disrupting Sagittarius dwarf galaxy in this framework. Using a
realistic baryonic mass model for the Milky Way, we attempt to reproduce the
present-day spatial and kinematic structure of the Sagittarius dwarf and its
immense tidal stream that wraps around the Milky Way. With very little freedom
on the original structure of the progenitor, constrained by the total
luminosity of the Sagittarius structure and by the observed stellar mass-size
relation for isolated dwarf galaxies, we find reasonable agreement between our
simulations and observations of this system. The observed stellar velocities in
the leading arm can be reproduced if we include a massive hot gas corona around
the Milky Way that is flattened in the direction of the principal plane of its
satellites. This is the first time that tidal dissolution in MOND has been
tested rigorously at these mass and acceleration scales.
