Hubble Diagram Dispersion From Large-Scale Structure

TL;DR

This paper investigates how large-scale structures like voids in the universe affect the Hubble diagram, showing they cause small magnitude changes and introduce dispersion that can bias cosmological measurements.

Contribution

It provides a non-linear analysis of large-scale structure effects on luminosity distances using a Swiss Cheese model, highlighting potential biases in cosmological observations.

Findings

Void-induced magnitude changes are less than 0.012 for intervening voids.

Sources inside voids can be significantly affected at z<0.5.

Inhomogeneities cause dispersion and potential bias in cosmological measurements.

Abstract

We consider the effects of large structures in the Universe on the Hubble diagram. This problem is treated non-linearly by considering a Swiss Cheese model of the Universe in which under-dense voids are represented as negatively curved regions of space-time. Exact expressions for luminosity distances and redshifts are used to investigate the non-linear effects of structure on the magnitudes of astrophysical sources. It is found that the intervening voids we consider, between the observer and source, produce changes in apparent magnitude of less than 0.012. Sources inside voids, however, can be affected considerably at redshifts below z~0.5. By averaging observable quantities over many randomly generated distributions of voids we find that the presence of these structures has the effect of introducing a dispersion around the mean, which itself can be displaced the background value. Observers in an inhomogeneous universe, who take averages of observables along many different lines of sight, may then introduce systematic biases, and under-estimate errors, if these effects are not taken into account. Estimates of the potential size of these effects are made using data from simulated large-scale structure.