Double-Kasner Spacetime: Peculiar Velocities and Cosmic Jets

TL;DR

This paper investigates how peculiar velocities and cosmic jet formations occur in dynamic, collapsing spacetimes, especially in Kasner and double-Kasner models, highlighting the effects of inhomogeneities on these phenomena.

Contribution

It demonstrates the formation of double-jet structures in collapsing spacetimes and analyzes the impact of spatial inhomogeneities on their persistence.

Findings

Double-jet configurations form in Kasner spacetime.

Spatial inhomogeneities can alter jet structures.

Jets can persist temporarily despite inhomogeneities.

Abstract

In dynamic spacetimes in which asymmetric gravitational collapse/expansion is taking place, the timelike geodesic equation appears to exhibit an interesting property: Relative to the collapsing configuration, free test particles undergo gravitational "acceleration" and form a double-jet configuration parallel to the axis of collapse. We illustrate this aspect of peculiar motion in simple spatially homogeneous cosmological models such as the Kasner spacetime. To estimate the effect of spatial inhomogeneities on cosmic jets, timelike geodesics in the Ricci-flat double-Kasner spacetime are studied in detail. While spatial inhomogeneities can significantly modify the structure of cosmic jets, we find that under favorable conditions the double-jet pattern can initially persist over a finite period of time for sufficiently small inhomogeneities.