Geodesics in a quasispherical spacetime: A case of gravitational repulsion

TL;DR

This paper investigates geodesic behavior in a specific Weyl spacetime, revealing how deviations from spherical symmetry, especially quadrupole moments, can lead to phenomena like gravitational repulsion near the $r=2M$ surface.

Contribution

It introduces the M--Q solution as a suitable model for strong quasi-spherical gravitational fields and analyzes how geodesics differ from the spherical case, highlighting effects like gravitational repulsion.

Findings

Geodesics are sensitive to deviations from spherical symmetry.

Radial acceleration can change sign near the $r=2M$ surface.

Quadrupole moments influence the gravitational behavior significantly.

Abstract

Geodesics are studied in one of the Weyl metrics, referred to as the M--Q solution. First, arguments are provided, supporting our belief that this space--time is the more suitable (among the known solutions of the Weyl family) for discussing the properties of strong quasi--spherical gravitational fields. Then, the behaviour of geodesics is compared with the spherically symmetric situation, bringing out the sensitivity of the trajectories to deviations from spherical symmetry. Particular attention deserves the change of sign in proper radial acceleration of test particles moving radially along symmetry axis, close to the $r=2M$ surface, and related to the quadrupole moment of the source.