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CMB cold spot explanation proposed (looks good)

by marcus
Tags: cmb coldspot, sachs-wolfe, void
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marcus
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Jul9-14, 09:45 PM
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Joe Silk is one of the co-authors. One expects large voids in the distribution of galaxies because of the cobwebby way dark and ordinary matter have condensed.
A large void comparatively close by (within a few billion LY of us) could cool ancient background light passing thru on its way to us. Until now no large void was found, in the direction of the famous CMB cold spot.

Now one has been found! So it offers a possible explanation for the otherwise puzzling cold spot.
http://arxiv.org/abs/1406.3622
The Cold Spot in the Cosmic Microwave Background: the Shadow of a Supervoid
István Szapudi, András Kovács, Benjamin R. Granett, Zsolt Frei, Joseph Silk, Juan Garcia-Bellido, Will Burgett, Shaun Cole, Peter W. Draper, Daniel J. Farrow, Nicholas Kaiser, Eugene A. Magnier, Nigel Metcalfe, Jeffrey S. Morgan, Paul Price, John Tonry, Richard Wainscoat
(Submitted on 15 Jun 2014)
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.
8 pages, 4 figures, to appear in the proceedings of the Moriond Cosmology Conference 2014
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marcus
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Jul9-14, 10:22 PM
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From Wikipedia article on the Integrated Sachs Wolfe (ISW) effect.
==quote http://en.wikipedia.org/wiki/Sachs–Wolfe_effect ==
The full nonlinear (linear + higher-order) late-time ISW effect, especially in the case of individual voids and clusters, is sometimes known as the Rees–Sciama effect, since Martin Rees and Dennis Sciama elucidated the following physical picture.[2]

Accelerated expansion due to dark energy causes even strong large-scale potential wells (superclusters) and hills (voids) to decay over the time it takes a photon to travel through them. A photon gets a kick of energy going into a potential well (a supercluster), and it keeps some of that energy after it exits, after the well has been stretched out and shallowed. Similarly, a photon has to expend energy entering a supervoid, but will not get all of it back upon exiting the slightly squashed potential hill.[/quote]


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