2024ApJ...971...19C

An analysis of the cosmological constant Ω_Λ fitted to subsamples of the Pantheon+ Type Ia supernova sample spanning 2π steradians for a grid of 432 pole positions covering the whole sky reveals two large-scale asymmetries. One of them is closely aligned with the Galactic north-south direction and the other points approximately toward R.A. ∼ 217.°5, decl. ∼ -26.°4, ∼50.°9 from the cosmic microwave background dipole Apex. The signal-to-noise ratio (S/N) of the multiple Ω_Λ measurements in these directions is 3.2 ≲ S/N ≲ 8.4. The first asymmetry is puzzling, and would indicate a systematic effect related with the distribution of Pantheon+ supernovae on the sky and, probably, how the correction for reddening in the Galaxy is calculated. The second one, which entails a 2.8-σ tension between Ω_Λ measured in opposite directions, bears strong implications on our interpretation of Ω_Λ as dark energy: it is consistent with the prediction for tilted observers located in a Friedmann-Robertson-Walker universe who could measure an acceleration or a deceleration with a dipolar asymmetry, irrespective of what the universe as a whole is doing. In this case, Ω_Λ would not be a physical entity, a real dark energy, but an apparent effect associated with the relativistic frame of reference transformation.