Orbital evidences for dark-matter-free Milky Way dwarf spheroidal
  galaxies
  The nature of Milky Way dwarf spheroidals (MW dSphs) has been questioned, in
particular whether they are dominated by dark matter (DM). Here we investigate
an alternative scenario, for which tidal shocks are exerted by the MW to
DM-free dSphs after a first infall of their gas-rich progenitors, and for which
theoretical calculations have been verified by pure N-body simulations. Whether
or not the dSphs are on their first infall cannot be resolved on the sole basis
of their star formation history. In fact, gas removal may cause complex
gravitational instabilities and near-pericenter passages can give rise to tidal
disruptive processes. Advanced precision with the Gaia satellite in determining
both their past orbital motions and the MW velocity curve is, however,
providing crucial results.
  First, tidal shocks explain why DM-free dSphs are found preferentially near
their pericenter, where they are in a destructive process, while their chance
to be long-lived satellites is associated with a very low probability P~ 2
10^-7, which is at odds with the current DM-dominated dSph scenario. Second,
most dSph binding energies are consistent with a first infall. Third, the MW
tidal shocks that predict the observed dSph velocity dispersions are themselves
predicted in amplitude by the most accurate MW velocity curve. Fourth, tidal
shocks accurately predict the forces or accelerations exerted at half-light
radius of dSphs, including the MW and the Magellanic System gravitational
attractions.
  The above is suggestive of dSphs that are DM-free and tidally shocked near
their pericenters, which may provoke a significant quake in our understanding
of near-field cosmology.
