View source for Astronomy:CMB cold spot

{{Short description|Region in space}}

[[File:Eridanus supervoid in celestial sphere.png|thumb|400px|The circled area is the cold spot. Black lines in the Planck's CMB map indicates each constellation, cold spot is in Eridanus constellation. The blue circle is the equatorial line in the celestial sphere. Image generated with Celestia.]]
[[File:ColdSpot.jpg|thumb|The circled area is the cold spot in the WMAP.]]

The '''CMB Cold Spot''' or '''WMAP Cold Spot''' is a region of the sky seen in [[Physics:Microwave|microwave]]s that has been found to be unusually large and cold relative to the expected properties of the [[Astronomy:Cosmic microwave background|cosmic microwave background radiation]] (CMBR). The "Cold Spot" is approximately 70&nbsp;µK (0.00007&nbsp;[[Kelvin|K]]) colder than the average CMB temperature (approximately 2.7&nbsp;K), whereas the [[Root mean square|root mean square]] of typical temperature variations is only 18&nbsp;µK.<ref>{{cite book |last=Wright |first=E.L. |year=2004 |chapter=Theoretical Overview of Cosmic Microwave Background Anisotropy |editor=W. L. Freedman |title=Measuring and Modeling the Universe |series=Carnegie Observatories Astrophysics Series |publisher={{wipe|Cambridge University Press}} |page=291 |isbn=978-0-521-75576-4 |arxiv=astro-ph/0305591|bibcode = 2004mmu..symp..291W }}</ref><ref group="note">After the [[Physics:Dipole|dipole]] anisotropy, which is due to the Doppler shift of the microwave background radiation due to our [[Astronomy:Peculiar velocity|peculiar velocity]] relative to the comoving cosmic rest frame, has been subtracted out. This feature is consistent with the Earth moving at some 627&nbsp;km/s towards the constellation [[Astronomy:Virgo (constellation)|Virgo]].</ref> At some points, the "cold spot" is 140&nbsp;µK colder than the average CMB temperature.<ref>{{cite news |last1=Woo |first1=Marcus |title=The largest thing in the universe |url=http://www.bbc.com/earth/story/20150723-the-largest-thing-in-the-universe |accessdate=14 August 2015 |publisher=BBC}}</ref>

The radius of the "cold spot" [[Subtended angle|subtends]] about 5°; it is centered at the [[Galactic coordinate system|galactic coordinate]] {{nowrap|1=''l''<sub>''II''</sub> = 207.8°}}, {{nowrap|1=''b''<sub>''II''</sub> = −56.3°}} ([[Astronomy:Equatorial coordinate system|equatorial]]: [[Right ascension|''α'']] = {{RA|03|15|05}}, [[Declination|''δ'']] = {{Dec|−19|35|02}}). It is, therefore, in the Southern Celestial Hemisphere, in the direction of the constellation [[Astronomy:Eridanus (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''' that may exist between us and the primordial CMB (foreground voids can cause cold spots against the CMB). Such a [[Astronomy:Void|void]] would affect the observed CMB via the integrated Sachs–Wolfe effect, and would be one of the largest structures in the [[Astronomy:Observable universe|observable universe]]. This would be an extremely large region of the universe, roughly 150 to 300 Mpc or 500 million to one billion [[Astronomy:Light-year|light-year]]s across and 6 to 10 billion light years away,<ref name="space.newscientist.com">{{cite journal |url=https://www.newscientist.com/article/mg19626311.400-the-void-imprint-of-another-universe.html |title=The void: Imprint of another universe? |journal=New Scientist |doi=10.1016/s0262-4079(07)62977-7
 |last=Chown |first=Marcus |volume=196 |issue=2631 |pages=34–37 |year=2007}}</ref> at redshift <math>z\simeq 1</math>, containing a density of matter much smaller than the average density at that redshift.{{Citation needed|date=September 2013}}

==Discovery and significance==
[[File:Eridanus supervoid.jpg|300px|thumb|CMB Cold Spot was also observed by the Planck satellite at similar significance. Image generated with Celestia Program.]]
In the first year of data recorded by the [[Astronomy:Wilkinson Microwave Anisotropy Probe|Wilkinson Microwave Anisotropy Probe]] (WMAP), a region of sky in the constellation [[Astronomy:Eridanus (constellation)|Eridanus]] was found to be cooler than the surrounding area.<ref>{{cite journal |arxiv=astro-ph/0405341 |last1=Cruz |first1=M. |title=Detection of a non-Gaussian Spot in WMAP |journal=Monthly Notices of the Royal Astronomical Society |volume=356 |issue=1 |pages=29–40 |last2=Martinez-Gonzalez |first2=E. |last3=Vielva |first3=P. |last4=Cayon |first4=L. |year=2005 |doi=10.1111/j.1365-2966.2004.08419.x |bibcode=2005MNRAS.356...29C}}</ref> Subsequently, using the data gathered by WMAP over 3 years, the statistical significance of such a large, cool region was estimated. The probability of finding a deviation at least as high in [[Gaussian random field|Gaussian]] simulations was found to be 1.85%.<ref>{{cite journal |arxiv=astro-ph/0603859 |last1=Cruz |first1=M. |title=The non-Gaussian Cold Spot in the 3-year WMAP data |journal=The Astrophysical Journal |volume=655 |issue=1 |pages=11–20 |last2=Cayon |first2=L. |last3=Martinez-Gonzalez |first3=E. |last4=Vielva |first4=P. |last5=Jin |first5=J. |year=2007 |doi=10.1086/509703 |bibcode=2007ApJ...655...11C|s2cid=121935762 }}</ref> Thus it appears unlikely, but not impossible, that the cold spot was generated by the standard mechanism of [[Physics:Quantum fluctuation|quantum fluctuation]]s during cosmological inflation, which in most inflationary models gives rise to Gaussian statistics. The cold spot may also, as suggested in the references above, be a signal of non-Gaussian primordial fluctuations.

Some authors called into question the statistical significance of this cold spot.<ref name="arxiv.org">{{cite journal |arxiv=0908.3988 |last1=Zhang |first1=Ray |title=Disks in the sky: A reassessment of the WMAP "cold spot" |journal=Astroparticle Physics |volume=33 |issue=2 |page=69 |last2=Huterer |first2=Dragan |year=2010 |doi=10.1016/j.astropartphys.2009.11.005 |bibcode=2010APh....33...69Z|citeseerx=10.1.1.249.6944 |s2cid=5552896 }}</ref>

In 2013, the CMB Cold Spot was also observed by the [[Engineering:Planck (spacecraft)|Planck]] satellite<ref>{{cite journal |arxiv=1303.5083 |doi=10.1051/0004-6361/201321534 |last1=Ade |first1=P. A. R. |display-authors=0 |collaboration=Planck Collaboration |title=Planck 2013 results. XXIII. Isotropy and statistics of the CMB |journal=Astronomy & Astrophysics |volume=571 |page=A23 |year=2013 |bibcode=2014A&A...571A..23P|s2cid=13037411 }}</ref> at similar significance, discarding the possibility of being caused by a systematic error of the WMAP satellite.

==Possible causes other than primordial temperature fluctuation==
The large 'cold spot' forms part of what has been called an '[[Astronomy:Axis of evil (cosmology)|axis of evil]]' (so-called because it was unexpected to see a structure like this).<ref>{{cite web |author=Milligan on March 22, 2006 10:31 PM |url=http://blog.lib.umn.edu/mill1974/EGAD/041107.html |title=WMAP: The Cosmic Axis of Evil – EGAD |publisher=Blog.lib.umn.edu |accessdate=2014-05-11 |archive-url=https://web.archive.org/web/20150607015628/http://blog.lib.umn.edu/mill1974/EGAD/041107.html |archive-date=2015-06-07}}</ref>

===Supervoid===
[[File:Mean void imprint.png|thumb|168px|The mean ISW imprint 50 supervoids have on the Cosmic Microwave Background:<ref name="graneypudi">{{cite journal |arxiv=0805.3695 |last1=Granett |first1=Benjamin R. |title=An Imprint of Super-Structures on the Microwave Background due to the Integrated Sachs–Wolfe Effect |journal=The Astrophysical Journal |volume=683 |issue=2 |pages=L99–L102 |last2=Neyrinck |first2=Mark C. |last3=Szapudi |first3=István |year=2008 |doi=10.1086/591670 |bibcode=2008ApJ...683L..99G|s2cid=15976818 }}</ref>{{Clarify |date=December 2013}} color scale from -20 to +20&nbsp;µK.]]

One possible explanation of the cold spot is a huge [[Astronomy:Void|void]] between us and the primordial CMB. A region cooler than surrounding sightlines can be observed if a large void is present, as such a void would cause an increased cancellation between the "late-time" integrated [[Astronomy:Sachs–Wolfe effect|Sachs–Wolfe effect]] and the "ordinary" Sachs–Wolfe effect.<ref>{{cite journal |arxiv=astro-ph/0602478 |author1=Kaiki Taro Inoue |title=Local Voids as the Origin of Large-angle Cosmic Microwave Background Anomalies I |journal=The Astrophysical Journal |volume=648 |issue=1 |pages=23–30 |last2=Silk |first2=Joseph |year=2006 |doi=10.1086/505636 |bibcode=2006ApJ...648...23I|s2cid=119080005 }}</ref> This effect would be much smaller if [[Astronomy:Dark energy|dark energy]] were not stretching the void as [[Physics:Photon|photon]]s went through it.<ref name="supervoid2015">{{cite journal |title=Detection of a supervoid aligned with the cold spot of the cosmic microwave background |journal=Monthly Notices of the Royal Astronomical Society |volume=450 |issue=1 |pages=288–294 |year=2015 |doi=10.1093/mnras/stv488 |arxiv=1405.1566 |bibcode=2015MNRAS.450..288S |last1=Szapudi |first1=I. |display-authors=0}}
*{{cite web |date=April 20, 2015 |title=Cold cosmic mystery solved: Largest known structure in the universe leaves its imprint on CMB radiation |website=Phys.org |url=http://phys.org/news/2015-04-cold-cosmic-mystery-largest-universe.html}}</ref>

''Rudnick et al''.<ref>{{cite journal |arxiv=0704.0908 |last1=Rudnick |first1=Lawrence |title=Extragalactic Radio Sources and the WMAP Cold Spot |journal=The Astrophysical Journal |volume=671 |issue=1 |pages=40–44 |last2=Brown |first2=Shea |last3=Williams |first3=Liliya R. |year=2007 |doi=10.1086/522222 |bibcode=2007ApJ...671...40R|s2cid=14316362 }}</ref> found a dip in [[Astronomy:NRAO VLA Sky Survey|NVSS]] galaxy number counts in the direction of the Cold Spot, suggesting the presence of a large void. Since then, some additional works have cast doubt on the "supervoid" explanation. The correlation between the NVSS dip and the Cold Spot was found to be marginal using a more conservative statistical analysis.<ref>{{cite journal |arxiv=0805.2751 |last1=Smith |first1=Kendrick M. |title=No evidence for the cold spot in the NVSS radio survey |journal=Monthly Notices of the Royal Astronomical Society |volume=403 |issue=2 |page=2 |last2=Huterer |first2=Dragan |year=2010 |doi=10.1111/j.1365-2966.2009.15732.x |bibcode=2010MNRAS.403....2S|s2cid=16043676 }}</ref> Also, a direct survey for galaxies in several one-degree-square fields within the Cold Spot found no evidence for a supervoid.<ref>{{cite journal |arxiv=0911.2223 |last1=Granett |first1=Benjamin R. |title=Galaxy Counts on the CMB Cold Spot |journal=The Astrophysical Journal |volume=714 |issue=825 |pages=825–833 |last2=Szapudi |first2=István |last3=Neyrinck |first3=Mark C. |year=2010 |doi=10.1088/0004-637X/714/1/825 |bibcode=2010ApJ...714..825G|s2cid=118614796 }}</ref> However, the supervoid explanation has not been ruled out entirely; it remains intriguing, since supervoids do seem capable of affecting the CMB measurably.<ref name="graneypudi" /><ref>[http://www.ifa.hawaii.edu/cosmowave/supervoids Dark Energy and the Imprint of Super-Structures on the Microwave Background]</ref><ref>{{Cite journal |arxiv=1405.1555 |title=A Supervoid Imprinting the Cold Spot in the Cosmic Microwave Background |journal=Monthly Notices of the Royal Astronomical Society |volume=455 |issue=2 |pages=1246 |year=2014 |last1=Finelli |first1=Fabio |last2=Garcia-Bellido |first2=Juan |last3=Kovacs |first3=Andras |last4=Paci |first4=Francesco |last5=Szapudi |first5=Istvan |doi=10.1093/mnras/stv2388 |bibcode=2016MNRAS.455.1246F}}</ref>

A 2015 study shows the presence of a supervoid that has a diameter of 1.8 billion [[Light year|light year]]s and is centered at 3 billion light-years from our [[Astronomy:Milky Way|galaxy]] in the direction of the Cold Spot, likely being associated with it.<ref name="supervoid2015" /> This would make it the largest void detected, and one of the largest structures known.<ref name=Discovery>{{cite web
 |work=Discovery News
 |title=Mysterious 'Cold Spot': Fingerprint of Largest Structure in the Universe?
 |url=http://news.discovery.com/space/galaxies/mysterious-cold-spot-fingerprint-of-largest-structure-in-the-universe-150420.htm
 |date=2017-05-10
 |access-date=2015-05-28
 |archive-date=2015-10-31
 |archive-url=https://web.archive.org/web/20151031140959/http://news.discovery.com/space/galaxies/mysterious-cold-spot-fingerprint-of-largest-structure-in-the-universe-150420.htm
 |url-status=dead
 }}</ref><ref group=note name="note 1 group=note">A claim by Szapudi ''et al'' states that the newly found void is the "largest structure ever identified by humanity". However, another source reports that the largest structure is the [[Astronomy:Supercluster|supercluster]] corresponding to the NQ2-NQ4 GRB overdensity at 10 billion light years.</ref> Later measurements of the [[Astronomy:Sachs–Wolfe effect|Sachs–Wolfe effect]] show too its likely existence.<ref>{{Cite journal |arxiv=1608.08638 |title=A detection of the integrated Sachs-Wolfe imprint of cosmic superstructures using a matched-filter approach |journal=The Astrophysical Journal |volume=830 |issue=2016 |pages=L19 |year=2016 |last1=Seshadri |first1=Nadatur |last2=Crittenden |first2=Robert |doi=10.3847/2041-8205/830/1/L19 |bibcode=2016ApJ...830L..19N|s2cid=55896975 |doi-access=free }}</ref>

Although large voids are known in the universe, a void would have to be exceptionally vast to explain the cold spot, perhaps 1,000 times larger in volume than expected typical voids. It would be 6 billion–10 billion [[Astronomy:Light-year|light-year]]s away and nearly one billion light-years across, and would be perhaps even more improbable to occur in the large-scale structure than the WMAP cold spot would be in the primordial CMB.

A 2017 study<ref name=Mackenzie>{{cite journal |last1=Mackenzie |first1=Ruari |display-authors=0 |arxiv=1704.03814|year=2017 |title=Evidence against a supervoid causing the CMB Cold Spot |quote=Another explanation could be that the Cold Spot is the remnant of a collision between our Universe and another ‘bubble’ universe during an early inflationary phase (Chang et al. 2009, Larjo & Levi 2010). |doi=10.1093/mnras/stx931 |volume=470 |issue=2 |journal=Monthly Notices of the Royal Astronomical Society |pages=2328–2338|bibcode = 2017MNRAS.470.2328M }}</ref> reported surveys showing no evidence that associated voids in the line of sight could have caused the CMB Cold Spot and concluded that it may instead have a primordial origin.

One important thing to confirm or rule out the late time integrated Sachs–Wolfe effect is the mass profile of galaxies in the area as ISW effect is affected by the galaxy bias which depends on the mass profiles and types of galaxies.<ref name="Rahman2020">{{cite journal |last1=Rahman |first1=Syed Faisal ur |journal=Physics World |date=2020 |volume=33 |issue=2 |page=36 |url=https://physicsworld.com/a/the-enduring-enigma-of-the-cosmic-cold-spot/|title=The enduring enigma of the cosmic cold spot
|doi=10.1088/2058-7058/33/2/35 |bibcode=2020PhyW...33b..36R |s2cid=216440967 }}</ref><ref name="Dupe2011">{{cite journal |last1=Dupe |first1=F.X. |journal=Astronomy & Astrophysics |date=2011 |volume=534 |page=A51|title=Measuring the integrated Sachs–Wolfe effect|doi=10.1051/0004-6361/201015893 |arxiv=1010.2192 |bibcode=2011A&A...534A..51D |s2cid=14737577 }}</ref>

In December 2021, the [[Astronomy:Dark Energy Survey|Dark Energy Survey]] (DES), analyzing their data, put forward more evidence for the correlation between the Eridanus supervoid and the CMB cold spot.<ref>{{Cite journal|last1=Kovács|first1=A|last2=Jeffrey|first2=N|last3=Gatti|first3=M|last4=Chang|first4=C|last5=Whiteway|first5=L|last6=Hamaus|first6=N|last7=Lahav|first7=O|last8=Pollina|first8=G|last9=Bacon|first9=D|last10=Kacprzak|first10=T|last11=Mawdsley|first11=B|date=2021-12-17|title=The DES view of the Eridanus supervoid and the CMB cold spot|url=https://academic.oup.com/mnras/article/510/1/216/6468992|journal=Monthly Notices of the Royal Astronomical Society|language=en|volume=510|issue=1|pages=216–229|doi=10.1093/mnras/stab3309|issn=0035-8711|arxiv=2112.07699}}</ref><ref>{{Cite web|title=Our Universe is normal! Its biggest anomaly, the CMB cold spot, is now explained|url=https://bigthink.com/starts-with-a-bang/cmb-cold-spot/|access-date=2022-02-09|website=Big Think|date=February 2022 |language=en-US}}</ref>

===Cosmic texture===
In late 2007, (''Cruz et al.'')<ref>{{cite journal |journal=Science |doi=10.1126/science.1148694 |title=A Cosmic Microwave Background Feature Consistent with a Cosmic Texture |first=M. |last=Cruz |pmid=17962521 |author2=N. Turok |author3=P. Vielva |author4=E. Martínez-González |author5=M. Hobson |year=2007 |volume=318 |issue=5856 |pages=1612–4 |bibcode=2007Sci...318.1612C |arxiv=0710.5737|citeseerx=10.1.1.246.8138 |s2cid=12735226 }}</ref> argued that the Cold Spot could be due to a [[Astronomy:Texture (cosmology)|cosmic texture]], a remnant of a [[Physics:Phase transition|phase transition]] in the early Universe.

===Parallel universe===
A controversial claim by [[Biography:Laura Mersini-Houghton|Laura Mersini-Houghton]] is that it could be the imprint of [[Physics:Multiverse|another universe]] beyond our own, caused by [[Quantum entanglement|quantum entanglement]] between universes before they were separated by [[Astronomy:Cosmic inflation|cosmic inflation]].<ref name="space.newscientist.com" /> Laura Mersini-Houghton said, "Standard cosmology cannot explain such a giant cosmic hole" and made the hypothesis that the WMAP cold spot is "… the unmistakable imprint of another universe beyond the edge of our own." If true, this provides the first [[Empirical evidence|empirical evidence]] for a parallel universe (though theoretical models of parallel universes existed previously). It would also support [[Physics:String theory|string theory]].{{Citation needed|date=January 2013}} The team claims that there are [[Philosophy:Testability|testable]] consequences for its theory. If the parallel-universe theory is true, there will be a similar void in the [[Celestial sphere]]'s opposite hemisphere<ref>{{cite journal |arxiv=hep-th/0611223 |last1=Holman |first1=R. |title=Cosmological Avatars of the Landscape I: Bracketing the SUSY Breaking Scale |journal=Physical Review D |volume=77 |issue=6 |page=063510 |last2=Mersini-Houghton |first2=L. |last3=Takahashi |first3=Tomo |year=2008 |doi=10.1103/PhysRevD.77.063510 |bibcode=2008PhRvD..77f3510H|s2cid=118887165 }}</ref><ref>{{cite journal |arxiv=hep-th/0612142 |last1=Holman |first1=R. |title=Cosmological Avatars of the Landscape II: CMB and LSS Signatures |journal=Physical Review D |volume=77 |issue=6 |page=063511 |last2=Mersini-Houghton |first2=Laura |last3=Takahashi |first3=Tomo |year=2008 |doi=10.1103/PhysRevD.77.063511 |bibcode=2008PhRvD..77f3511H|s2cid=41377003 }}</ref> (which ''New Scientist'' reported to be in the Southern celestial hemisphere; the results of the New Mexico array study reported it as being in the Northern).<ref name="space.newscientist.com" />

Other researchers have modeled the cold spot as potentially the result of cosmological bubble collisions, again before inflation.<ref>{{Cite journal |arxiv=0810.5128 |last1=Chang |first1=Spencer |title=Watching Worlds Collide: Effects on the CMB from Cosmological Bubble Collisions |journal=Journal of Cosmology and Astroparticle Physics |volume=2009 |issue=4 |pages=025 |last2=Kleban |first2=Matthew |last3=Levi |first3=Thomas S. |year=2009 |doi=10.1088/1475-7516/2009/04/025|bibcode = 2009JCAP...04..025C |s2cid=15683857 }}</ref><ref>{{cite journal |doi=10.1088/1475-7516/2010/12/023 |title=Polarizing bubble collisions |journal=Journal of Cosmology and Astroparticle Physics |volume=2010 |issue=12 |pages=023 |year=2010 |last1=Czech |first1=Bartłomiej |last2=Kleban |first2=Matthew |last3=Larjo |first3=Klaus |last4=Levi |first4=Thomas S |last5=Sigurdson |first5=Kris |bibcode=2010JCAP...12..023C|arxiv = 1006.0832 |s2cid=250776263 }}</ref><ref name=Mackenzie/>

A sophisticated computational analysis (using [[Kolmogorov complexity]]) has derived evidence for a north and a south cold spot in the satellite data:<ref>{{cite journal |doi=10.1051/0004-6361/200911625 |title=Kolmogorov cosmic microwave background sky |journal=Astronomy and Astrophysics |volume=497 |issue=2 |page=343 |year=2009 |last1=Gurzadyan |first1=V. G. |display-authors=0 |arxiv=0811.2732 |bibcode=2009A&A...497..343G|s2cid=16262725 }}</ref> "...among the high randomness regions is the southern non-Gaussian anomaly, the Cold Spot, with a stratification expected for the voids. Existence of its counterpart, a Northern Cold Spot with almost identical randomness properties among other low-temperature regions is revealed."

These predictions and others were made prior to the measurements (see Laura Mersini).{{Citation needed|date=February 2013}} However, apart from the Southern Cold Spot, the varied statistical methods in general fail to confirm each other regarding a Northern Cold Spot.<ref>{{cite journal |arxiv=0905.2854 |last1=Rossmanith |first1=G. |title=Non-Gaussian Signatures in the five-year WMAP data as identified with isotropic scaling indices |journal=Monthly Notices of the Royal Astronomical Society |volume=399 |issue=4 |pages=1921–1933 |last2=Raeth |first2=C. |last3=Banday |first3=A. J. |last4=Morfill |first4=G. |year=2009 |doi=10.1111/j.1365-2966.2009.15421.x |bibcode=2009MNRAS.399.1921R|s2cid=11586058 }}</ref> The 'K-map' used to detect the Northern Cold Spot was noted to have twice the measure of randomness measured in the standard model. The difference is speculated to be caused by the randomness introduced by voids (unaccounted-for voids were speculated to be the reason for the increased randomness above the standard model).<ref>{{cite journal |arxiv=0810.3289 |last1=Gurzadyan |first1=V. G. |title=Kolmogorov stochasticity parameter measuring the randomness in Cosmic Microwave Background |journal=Astronomy and Astrophysics |volume=492 |issue=2 |pages=L33 |last2=Kocharyan |first2=A. A. |year=2008 |doi=10.1051/0004-6361:200811188 |bibcode=2008A&A...492L..33G}}</ref>

===Sensitivity to finding method===
The cold spot is mainly anomalous because it stands out compared to the relatively hot ring around it; it is not unusual if one only considers the size and coldness of the spot itself.<ref name="arxiv.org" /> More technically, its detection and significance depends on using a compensated filter like a [[Mexican hat wavelet]] to find it.{{citation needed|date=November 2021}}

==See also==
{{div col|colwidth=30em}}
* [[Astronomy:CfA2 Great Wall|CfA2 Great Wall]]
* [[Astronomy:Cosmic microwave background|Cosmic microwave background]]
* [[Astronomy:Dark flow|Dark flow]]
* [[Astronomy:Great Attractor|Great Attractor]]
* [[Astronomy:List of largest cosmic structures#List of largest voids|List of largest voids]]
* Sloan Great Wall
* [[Astronomy:South Pole Wall|South Pole Wall]]
* [[Astronomy:Void|Void]]
* [[Astronomy:Wilkinson Microwave Anisotropy Probe|Wilkinson Microwave Anisotropy Probe]]
{{div col end}}

==Notes==
{{Reflist|group=note}}

==References==
{{Reflist|30em}}

==External links==
* [http://www.solstation.com/x-objects/greatvoi.htm Great Void in Eridanus, (WMAP Cold Spot)]
* [https://web.archive.org/web/20070930032951/http://www.dailytech.com/Gaping+Hole+Found+in+Universe/article8598.htm Gaping Hole Found in Universe], Daily Tech
* [http://www.space.com/scienceastronomy/070823_huge_hole.html Huge Hole Found in the Universe], Space.com, 2007-08-23
* [https://web.archive.org/web/20070830195536/http://news.nationalgeographic.com/news/2007/08/070824-hole-sky.html Gaping "Hole" in the Sky Found, Experts Say], National Geographic News
* [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}}

[[Category:Voids (astronomy)]]
[[Category:Eridanus (constellation)]]
[[Category:Cosmic background radiation]]

{{Sourceattribution|CMB cold spot}}