Identification of the Long Stellar Stream of the Prototypical Massive
  Globular Cluster $\omega$ Centauri
  Omega Centauri is the most massive globular cluster of the Milky Way, and
possesses many peculiar properties. In particular, the cluster contains
distinct multiple stellar populations, with a large spread in metallicity and
different kinematics as a function of light elements abundance, implying that
it formed over an extended period of time. This has lead to the suggestion that
$\omega$ Cen is the remnant core of an accreted dwarf galaxy. If this scenario
is correct, $\omega$ Cen should be tidally limited, and one should expect to
find tidal debris spread along its orbit. Here we use N-body simulations to
show that the recently-discovered `Fimbulthul' structure, identified in the
second data release (DR2) of the Gaia mission, is the long sought-for tidal
stream of $\omega$ Cen, extending up to $28\deg$ from the cluster. Follow-up
high-resolution spectroscopy of 5 stars in the stream show that they are
closely-grouped in velocity, and have metallicities consistent with having
originated in that cluster. Guided by our N-body simulations, we devise a
selection filter that we apply to Gaia data to also uncover the portion of the
stream in the highly-contaminated and crowded field within $10\deg$ of $\omega$
Cen. Further modelling of the stream may help to constrain the dynamical
history of the dwarf galaxy progenitor of this disrupting system and guide
future searches for its remnant stars in the Milky Way.
