The Galactic Centre star S2 as a dynamical probe for intermediate-mass
  black holes
  We study the short-term effects of an intermediate mass black hole (IBH) on
the orbit of star S2 (S02), the shortest-period star known to orbit the
supermassive black hole (MBH) in the centre of the Milky Way. Near-infrared
imaging and spectroscopic observations allow an accurate determination of the
orbit of the star. Given S2's short orbital period and large eccentricity,
general relativity (GR) needs to be taken into account, and its effects are
potentially measurable with current technology. We show that perturbations due
to an IBH in orbit around the MBH can produce a shift in the apoapsis of S2
that is as large or even larger than the GR shift. An IBH will also induce
changes in the plane of S2's orbit at a level as large as one degree per
period. We apply observational orbital fitting techniques to simulations of the
S-cluster in the presence of an IBH and find that an IBH more massive than
about 1000 solar masses at the distance of the S-stars will be detectable at
the next periapse passage of S2, which will occur in 2018.
