CMB cold spot

<a href="/facts/Celestial_coordinate_system/23HhqvHj">Coordinates</a>: <a href="http://www.wikisky.org/?ra=3.2513888888889&de=-19.583888888889&zoom=1&show_grid=1&show_constellation_lines=1&show_constellation_boundaries=1&show_const_names=1&show_galaxies=1&img_source=IMG_all">03h 15m 05s, −19° 35′ 02″</a>

The CMB Cold Spot or WMAP Cold Spot is a region of the sky seen in <a href="/facts/Microwave/HmVSN31Y">microwaves</a> that has been found to be unusually large and cold relative to the expected properties of the <a href="/facts/Cosmic_microwave_background/ThB2HkLS">cosmic microwave background radiation</a> (CMBR). The "Cold Spot" is approximately 70 μK (0.00007 <a href="/facts/Kelvin/E3trzC4C">K</a>) colder than the average CMB temperature (approximately 2.7 K), whereas the <a href="/facts/Root_mean_square/Cfmg7dws">root mean square</a> of typical temperature variations is only 18 μK. At some points, the "cold spot" is 140 μK colder than the average CMB temperature.
The radius of the "cold spot" <a href="/facts/Subtended_angle/GQxln7lP">subtends</a> about 5°; it is centered at the <a href="/facts/Galactic_coordinate_system/Un6BambN">galactic coordinate</a> lII = 207.8°, bII = −56.3° (<a href="/facts/Equatorial_coordinate_system/dn5W4Eoo">equatorial</a>: <a href="/facts/Right_ascension/z4CEsTFu">α</a> = 03h 15m 05s, <a href="/facts/Declination/5X4S4k9u">δ</a> = −19° 35′ 02″). It is, therefore, in the <a href="/facts/Southern_Celestial_Hemisphere/PP2aeueF">Southern Celestial Hemisphere</a>, in the direction of the constellation <a href="/facts/Eridanus_(constellation)/cvtlSUun">Eridanus</a>.
Typically, the largest fluctuations of the primordial CMB temperature occur on angular scales of about 1°. Thus a cold region as large as the "cold spot" appears very unlikely, given generally accepted theoretical models. Various alternative explanations exist, including a so-called Eridanus Supervoid or Great Void that may exist between us and the primordial CMB (foreground voids can cause cold spots against the CMB). Such a <a href="/facts/Void_(astronomy)/Ue7kyYf0">void</a> would affect the observed CMB via the <a href="/facts/Integrated_Sachs%25E2%2580%2593Wolfe_effect/ydR1IqB8">integrated Sachs–Wolfe effect</a>, and would be one of the <a href="/facts/List_of_largest_known_cosmic_structures/amD8w2ID">largest structures</a> in the <a href="/facts/Observable_universe/CdTGMdsp">observable universe</a>. This would be an extremely large region of the universe, roughly 150 to 300 <a href="/facts/Megaparsec/SwSsk57J">Mpc</a> or 500 million to one billion <a href="/facts/Light-year/IGc5NdQb">light-years</a> across and 6 to 10 billion light years away, at redshift 
 
 
 
 z
 ≃
 1
 
 
 {\displaystyle z\simeq 1}
 
, containing a density of matter much smaller than the average density at that redshift.

CMB cold spot open-in-new

CMB cold spot