Geodesic Structure of the Accelerated Stephani Universe

TL;DR

This paper analyzes the geodesic structure of an accelerated Stephani universe, revealing how test particles and photons move, including radial velocity behavior and spiral trajectories, in a spherically symmetric cosmological model.

Contribution

It provides a detailed investigation of test particle and photon motion in an accelerated Stephani universe, highlighting observable effects and motion patterns.

Findings

Radial velocity decreases slightly over time for purely radial motion.

Particles and photons spiral outward when radial coordinate is constant.

Observable radial distance can increase with negative radial velocity.

Abstract

For the spherically symmetric Stephani cosmological model with an accelerated expansion, we investigate the main scenarios of the test particle and photon motion. We show that a comoving observer sees an appropriate picture. In the case of purely radial motion, the radial velocity decreases slightly with time due to the universe expansion. Both particles and photons spiral out of the center when the radial coordinate is constant. In the case of the motion with arbitrary initial velocity, the observable radial distance to the test particle can increase under negative observable radial velocity.