Volume 631, November 2019
|Number of page(s)||6|
|Section||Letters to the Editor|
|Published online||20 November 2019|
Letter to the Editor
Evidence for anisotropy of cosmic acceleration⋆
CNRS, UPMC, Institut d’Astrophysique de Paris, 98 bis Bld Arago, Paris, France
2 Niels Bohr Institute, University of Copenhagen, Blegdamsvej 17, 2100 Copenhagen, Denmark
3 Rudolf Peierls Centre for Theoretical Physics, University of Oxford, Parks Road, Oxford OX1 3PU, UK
Accepted: 18 October 2019
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.
Key words: cosmology: observations / dark energy / large-scale structure of Universe
The code used here is available at: https://github.com/rameez3333/Dipole_JLA
© ESO 2019
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