Cosmic Parallax as a probe of late time anisotropic expansion

TL;DR

Cosmic parallax, caused by anisotropic expansion, can be observed or constrained by Gaia, providing a new way to test models like voids or anisotropic dark energy at low redshifts.

Contribution

This paper demonstrates that Gaia and future astrometric missions can constrain anisotropic cosmological models through measurements of cosmic parallax.

Findings

Gaia can detect or limit anisotropic expansion effects.

Anisotropic dark energy models could produce observable cosmic parallax.

Future missions could improve constraints on anisotropic cosmologies.

Abstract

Cosmic parallax is the change of angular separation between pair of sources at cosmological distances induced by an anisotropic expansion. An accurate astrometric experiment like Gaia could observe or put constraints on cosmic parallax. Examples of anisotropic cosmological models are Lemaitre-Tolman-Bondi void models for off-center observers (introduced to explain the observed acceleration without the need for dark energy) and Bianchi metrics. If dark energy has an anisotropic equation of state, as suggested recently, then a substantial anisotropy could arise at $z \lesssim 1$ and escape the stringent constraints from the cosmic microwave background. In this paper we show that such models could be constrained by the Gaia satellite or by an upgraded future mission.