KBC Void

The KBC Void (or Local Hole) is an immense, comparatively empty region of space, named after astronomers Ryan Keenan, Amy Barger, and Lennox Cowie, who studied it in 2013.[1] The existence of a local under-density has been the subject of many pieces of literature and research articles, the kind of which were penned starting in the early 90s.[2][3]

Artist's conception of the KBC Void and the filaments and walls that surround it.

The under-density is proposed to be roughly spherical, approximately 2 billion light-years (600 megaparsecs, Mpc) in diameter. As other voids, it is not completely empty but contains the Milky Way, the Local Group, and a larger part of the Laniakea Supercluster. The Milky Way is within a few hundred million light-years of the void's centre.[4]

The existence of supervoids have been shown to be consistent with the standard cosmological model.[5] Galaxies inside a void experience a gravitational pull from outside the void and this yields a larger local value for the Hubble constant, a cosmological measure of how fast the universe expands. Some authors have proposed the structure as the cause of the discrepancy between measurements of the Hubble constant using galactic supernovae and Cepheid variables (72–75 km/s/Mpc) and from the cosmic microwave background and baryon acoustic oscillation data (67–68 km/s/Mpc).[6] However, other work has found no evidence for this in observations, finding the scale of the claimed under-density to be incompatible with observations which extend beyond its radius.[7]