Evidence for anisotropy of cosmic acceleration

Journal article

Observations reveal a “bulk flow” in the local Universe which is faster and extends to much larger scales than are expected around a typical observer in the standard ΛCDM cosmology. This is expected to result in a scale-dependent dipolar modulation of the acceleration of the expansion rate inferred from observations of objects within the bulk flow. From a maximum-likelihood analysis of the Joint Light-curve Analysis catalogue of Type Ia supernovae, we find that the deceleration parameter, in addition to a small monopole, indeed has a much bigger dipole component aligned with the cosmic microwave background dipole, which falls exponentially with redshift z: q0 = qm + qd.n̂ exp(-z/S). The best fit to data yields qd = −8.03 and S = 0.0262 (⇒d ∼ 100 Mpc), rejecting isotropy (qd = 0) with 3.9σ statistical significance, while qm = −0.157 and consistent with no acceleration (qm = 0) at 1.4σ. Thus the cosmic acceleration deduced from supernovae may be an artefact of our being non-Copernican observers, rather than evidence for a dominant component of “dark energy” in the Universe.

Authors: Colin, J; Mohayaee, R; Rameez, M; Sarkar, S

• Publication status: Published
• Peer review status: Peer reviewed
• Publisher: EDP Sciences
• Journal: Astronomy and Astrophysics
• Volume: 631
• Pages: L13-L13
• Publication date: 2019-11-20
• Acceptance date: 2019-10-18
• DOI: 10.1051/0004-6361/201936373
• EISSN: 1432-0746
• ISSN: 0004-6361
• Language: English
• Keywords: dark energy; large-scale structure of Universe; cosmology: observations