Constraints on the Local Cosmic Void from the Pantheon Supernovae Data

TL;DR

This study models the local cosmic void using segmented LTB metrics based on Pantheon supernovae data, finding limited anisotropy signals and constraints consistent with the standard cosmological model.

Contribution

It introduces a segmented LTB approach to reconstruct a more realistic, irregular local cosmic void profile using supernova data.

Findings

Weak anisotropy signals detected within void segments

Constraints are consistent with the ΛCDM model at 95% confidence level

Data insufficient to challenge cosmic homogeneity and isotropy

Abstract

In principle, the local cosmic void can be simply modeled by the spherically symmetric Lemaitre-Tolman-Bondi (LTB) metric. In practice, the real local cosmic void is probably not spherically symmetric. In this paper, to reconstruct a more realistic profile of the local cosmic void, we divide it into several segments. Each segment with certain solid angle is modeled by its own LTB metric. Meanwhile, we divide the 1048 type Ia supernovae (SNIa) of the Pantheon Survey into corresponding subsets according to their distribution in the galactic coordinate system. Obviously, each SNIa subset can only be used to reconstruct the profile of one segment. Finally, we can patch together an irregular profile for the local cosmic void with the whole Pantheon sample. Note that, the paucity of each data subset lead us to focus on the inner part of each void segment and assume that the half radii of the void segments are sufficient to constrain the whole segment. We find that, despite $2\sigma$ signals of anisotropy limited to the depth of the void segments, the constraints on every void segment are consistent with $\Lambda$CDM model at $95\%$ CL. Moreover, our constraints are too weak to challenge the cosmic homogeneity and isotropy.