Inhomogeneous cosmological models: exact solutions and their applications

Abstract

Recently, inhomogeneous generalisations of the Friedmann -Lemaître -Robertson -Walker cosmological models have gained interest in the astrophysical community and are more often employed to study cosmological phenomena. However, in many papers the inhomogeneous cosmological models are treated as an alternative to the FLRW models. In fact, they are not an alternative, but an exact perturbation of the latter, and are gradually becoming a necessity in modern cosmology. The assumption of homogeneity is just a first approximation introduced to simplify equations. So far this assumption is commonly believed to have worked well, but future and more precise observations will not be properly analysed unless inhomogeneities are taken into account. This paper reviews recent developments in the field and shows the importance of an inhomogeneous framework in the analysis of cosmological observations. § The subclass of isotropic pressure is usually credited to Misner and Sharp [122], and occasionally to Podurets [139].

Probing spatial homogeneity with LTB models: a detailed discussion

“…LTB models have already been covered at length in the literature (see e.g. Plebanski & Krasinski 2006;Enqvist 2008;Bolejko et al 2011, for many details). We therefore only briefly summarise the most important equations here.…”

“…This uncertainty inspired many to study inhomogeneous cosmologies (see Marra & Notari 2011;Bolejko et al 2011, for comprehensive reviews), including non-Copernican models that explain the apparent accelerated expansion of the Universe by means of radial inhomogeneities without requiring any form of dark energy. The basic idea behind these alternative models is quite simple because we know from observations and numerical simulations that the large-scale structure of the Universe consists of filaments and voids (see e.g.…”

Interactive mixture of inhomogeneous dark fluids driven by dark energy: a dynamical system analysis

“…These solutions have been extensively studied (with zero and nonzero cosmological constant) and used in a wide range of astrophysical and cosmological modelling (see extensive reviews in [29][30][31][32]). In particular, a better understanding of their theoretical properties follows by describing their dynamics in terms of "quasi-local scalars" [33][34][35][36] (to be denoted henceforth as "q-scalars"), which are related to averages of standard covariant scalars and satisfy FLRW dynamical equations and scaling laws [35].…”

Asymmetry and dark energy evolution

“…Using this assumption it is possible to fit the SNIa data without invoking DE [7]. Although it is a seductive idea, the initial program testing this against the observations seems to indicate that we need a void of a size never observed (gigaparsec in size) [8]. Research in these areas continues [9].…”