Standard inflationary hot big bang cosmology predicts small
fluctuations in the Cosmic Microwave Background (CMB) with
isotropic Gaussian statistics. All measurements support the
standard theory, except for a few anomalies discovered in the
Wilkinson Microwave Anisotropy Probe maps and confirmed recently
by the Planck satellite. The Cold Spot is one of the most
significant of such anomalies, and the leading explanation of it
posits a large void that imprints this extremely cold area via
the linear Integrated Sachs-Wolfe (ISW) effect due to the decay
of gravitational potentials over cosmic time, or via the Rees-
Sciama (RS) effect due to late-time non-linear evolution.
Despite several observational campaigns targeting the Cold Spot
region, to date no suitably large void was found at higher
redshifts z>0.3. Here we report the detection of an R=(192±15)h
−1Mpc size supervoid of depth δ=−0.13±0.03, and centred at
redshift z=0.22. This supervoid, possibly the largest ever
found, is large enough to significantly affect the CMB via the
non-linear RS effect, as shown in our Lemaitre-Tolman-Bondi
framework. This discovery presents the first plausible
explanation for any of the physical CMB anomalies, and raises
the possibility that local large-scale structure could be
responsible for other anomalies as well
