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Versione delle 10:30, 18 giu 2009

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'''[[:en:CMB cold spot]]'''

[[Image:ColdSpot.jpg|thumb|right|Circled 200px|L'area iscerchiata è thela coldmacchia spot.fredda]]

TheLa '''WMAPmacchia Coldfredda Spotnella radiazione cosmica di fondo''' oro '''CMBmacchia Coldfredda Spotdel [[WMAP]]''', isè auna regionporzione ofdella the[[Sfera skyceleste|volta seenceleste]] inche, se vista nelle [[microwavesmicroonde]], whichappare ispiù unusuallylarga largee andfredda coldrispetto relativealle toproprietà themedie expected properties of thedella [[cosmicradiazione microwavecosmica backgrounddi radiationfondo]] ('''CMB'''). ItMediamente, shouldla thoughfluttuazione betipica remembered that the typical fractionaldelle temperature fluctuations of thedella CMB areè ofnell'ordine orderdi 10^-5, andmentre thela "coldmacchia spot"fredda isè approximatelydi 70  [[Kelvin|µK]] colderpiù thanfredda thedella averagetemperatura CMBmedia temperaturedella CMB (approximatelyapprossimativamente di 2.,7 [[Kelvin|K]]).

TheIl radiusraggio ofdella themacchia "coldè spot" is aboutdi 5° circa; itil iscentro centeredsi attrova thealle [[GalacticSistema di coordinate systemgalattiche|galactic coordinate galattiche]]: l_''II'' = 207.8°, b_''II'' = −56.3° ([[Equatorial coordinate systemCoordinate_celesti#Coordinate_equatoriali|equatorialequatoriale]]: ''[[RightAscensione ascensionretta|''α'']]'': = 03^h15^m05^s, ''[[DeclinationDeclinazione (astronomia)|''δ'']]'' = −19^d35^m02^s). ThusQuesta itsi is in thetrova nell'[[SouthernEmisfero hemisphereaustrale|emisfero sud]] of thedella [[CelestialSfera sphereceleste|volta celeste]], innella the direction of the constellationcostellazione dell'[[EridanusEridano (costellazione)|Eridano]].

The radius of the "cold spot" is about 5°; it is centered at the [[Galactic coordinate system|galactic coordinate]] l_''II'' = 207.8°, b_''II'' = −56.3° ([[Equatorial coordinate system|equatorial]]: [[Right ascension|''α'']] = 03^h15^m05^s, [[Declination|''δ'']] = −19^d35^m02^s). Thus it is in the [[Southern hemisphere]] of the [[Celestial sphere]], in the direction of the constellation [[Eridanus]].

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'''. This would be an extremely large region of the universe, roughly 150 [[megaparsec|Mpc]] or 500 million [[light years]] across, at redshift <math>z\simeq 1</math>, containing a density of matter much smaller than the average density at that redshift. Such a void would affect the observed CMB via the [[Sachs-Wolfe effect|integrated Sachs-Wolfe effect]]. If a comparable [[supervoid]] did exist, it would be one of the [[large scale structure|largest structures]] in the observable Universe.

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*[http://news.bbc.co.uk/1/hi/sci/tech/6962185.stm BBC News: Great 'cosmic nothingness' found]. [[BBC News]], [[2007-08-24]]

{{Sky|03|15|05|-|19|35|02|1}}

<nowiki>[[Category:Voids]]

[[Category:Eridanus constellation]]