  Assuming spherical symmetry and weak field, it is shown that if one solves
the Poisson equation or the Einstein field equations sourced by a topological
defect, \ie~a singularity of a very specific form, the result is a localised
gravitational field capable of driving flat rotation (\ie~Keplerian circular
orbits at a constant speed for all radii) of test masses on a thin spherical
shell without any underlying mass. Moreover, a large-scale structure which
exploits this solution by assembling concentrically a number of such
topological defects can establish a flat stellar or galactic rotation curve,
and can also deflect light in the same manner as an equipotential (isothermal)
sphere. Thus the need for dark matter or modified gravity theory is mitigated,
at least in part.
