Testing the Isotropy of the Universe with Type Ia Supernovae

TL;DR

This study uses Type Ia supernova data to test the universe's isotropy, constraining anisotropy parameters and finding compatibility with isotropy but allowing for significant anisotropic deviations.

Contribution

It introduces an analysis of supernova data within an anisotropic Bianchi type I cosmological model considering anisotropic dark energy, providing new constraints on anisotropy parameters.

Findings

Constraints on anisotropy parameters: -0.16 < δ < 0.12 and -0.012 < Σ_0 < 0.012.

Supernova data compatible with an isotropic universe.

Large anisotropy levels are still permissible within current data.

Abstract

We analyze the magnitude-redshift data of type Ia supernovae included in the Union and Union2 compilations in the framework of an anisotropic Bianchi type I cosmological model and in the presence of a dark energy fluid with anisotropic equation of state. We find that the amount of deviation from isotropy of the equation of state of dark energy, the skewness \delta, and the present level of anisotropy of the large-scale geometry of the Universe, the actual shear \Sigma_0, are constrained in the ranges -0.16 < \delta < 0.12 and -0.012 < \Sigma_0 < 0.012 (1\sigma C.L.) by Union2 data. Supernova data are then compatible with a standard isotropic universe (\delta = \Sigma_0 = 0), but a large level of anisotropy, both in the geometry of the Universe and in the equation of state of dark energy, is allowed.