The binding of cosmological structures by massless topological defects

TL;DR

This paper demonstrates that certain topological defects can produce localized gravitational fields capable of explaining flat galactic rotation curves and light deflection without dark matter or modified gravity theories.

Contribution

It introduces a novel gravitational effect of topological defects that can mimic dark matter phenomena in galactic dynamics.

Findings

Topological defects can generate flat rotation curves.

Defects can cause light deflection similar to dark matter halos.

Multiple defects can produce large-scale galactic structures.

Abstract

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.