A (giant) void is not mandatory to explain away dark energy with a Lemaître-Tolman model

• Published in: Astronomy and astrophysics (Berlin) Vol. 518; no. 2; p. A21
• Main Authors: Célérier, M.-N., Bolejko, K., Krasiński, A.
• Format: Journal Article
• Language: English; French
• Published: Les Ulis EDP Sciences 01.07.2010
• Subjects: Astronomy; Astrophysics; cosmology: dark energy; cosmology: miscellaneous; Earth, ocean, space; Exact sciences and technology; Physics; Red shift; Tolman metric; Mass distribution; Evolution equation; cosmology: miscellaneous; Angular diameter; Space-time; Algorithms; Cosmology; Light cones; Models; Dark energy; Observables; cosmology: dark energy; Time constant; Current density
• ISSN: 0004-6361; 1432-0746; 1432-0756
• DOI: 10.1051/0004-6361/200913581

Context. Lemaître-Tolman (L-T) toy models with a central observer have been used to study the effect of large scale inhomogeneities on the SN Ia dimming. Claims that a giant void is mandatory to explain away dark energy in this framework are currently dominating. Aims. Our aim is to show that L-T models exist that reproduce a few features of the ΛCDM model, but do not contain the giant cosmic void. Methods. We propose to use two sets of data – the angular diameter distance together with the redshift-space mass-density and the angular diameter distance together with the expansion rate – both defined on the past null cone as functions of the redshift. We assume that these functions are of the same form as in the ΛCDM model. Using the Mustapha–Hellaby–Ellis algorithm, we numerically transform these initial data into the usual two L-T arbitrary functions and solve the evolution equation to calculate the mass distribution in spacetime. Results. For both models, we find that the current density profile does not exhibit a giant void, but rather a giant hump. However, this hump is not directly observable, since it is in a spacelike relation to a present observer. Conclusions. The alleged existence of the giant void was a consequence of the L-T models used earlier because their generality was limited a priori by needless simplifying assumptions, like, for example, the bang-time function being constant. Instead, one can feed any mass distribution or expansion rate history on the past light cone as initial data to the L-T evolution equation. When a fully general L-T metric is used, the giant void is not implied.