A Star Harbouring a Wormhole at its Core
  We consider a configuration consisting of a wormhole filled by a perfect
fluid. Such a model can be applied to describe stars as well as neutron stars
with a nontrivial topology. The presence of a tunnel allows for motion of the
fluid, including oscillations near the core of the system. Choosing the
polytropic equation of state for the perfect fluid, we obtain static regular
solutions. Based on these solutions, we consider small radial oscillations of
the configuration and show that the solutions are stable with respect to linear
perturbations in the external region.
