Metrically Stationary, Axially Symmetric, Isolated Systems in Quasi-Metric Gravity

TL;DR

This paper investigates axially symmetric, isolated spinning systems in quasi-metric gravity, finding that true stationarity is generally impossible except in weak-field, slow rotation cases, with implications for gravitational field modeling.

Contribution

It introduces an approximate solution for the exterior gravitational field of rotating sources in quasi-metric gravity, highlighting the non-existence of fully stationary solutions beyond certain orders.

Findings

Weak, slowly rotating sources can be approximated as stationary.

The gravito-magnetic metric resembles Kerr in the approximation.

A tidal quadrupole term appears, absent in Kerr.

Abstract

The gravitational field exterior respectively interior to an axially symmetric, metrically stationary, isolated spinning source made of perfect fluid is examined within the quasi-metric framework. (A metrically stationary system is defined as a system which is stationary except for the direct effects of the global cosmic expansion on the space-time geometry.) Field equations are set up and an attempt is made to find an approximate series solution for the exterior part. However, the result is that no stationary solution corresponding to a spinning source can exist when considering terms beyond a certain order in small quantities. That is, except for metrically static systems, axially symmetric systems must necessarily be non-stationary in quasi-metric gravity. However, sufficiently weak, axially symmetric gravitational fields associated with slowly rotating sources, may still be considered as stationary as an excellent approximation. Thus a truncated, approximately stationary solution is found for the exterior field. To lowest order in small quantities, the gravito-magnetic part of the found metric family corresponds with the Kerr metric in the metric approximation. On the other hand, the gravito-electric part of the found metric family also includes a tidal term characterized by the free quadrupole-moment parameter $J_2$ describing the effect of source deformation due to the rotation. This term has no counterpart in the Kerr metric. Finally, the geodetic effect for a gyroscope in orbit is calculated. There is a correction term, unfortunately barely too small to be detectable by Gravity Probe B, to the standard expression.