Editing Observable universe (section)

=== Cosmic Web: walls, filaments, nodes, and voids ===
[[File:Map of the Cosmic Web Generated from Slime Mould Algorithm.jpg|thumb|upright=1.8|Map of the cosmic web generated from a slime mould-inspired algorithm<ref>{{Cite web|url=https://www.spacetelescope.org/images/heic2003a/|title=Map of the Cosmic Web Generated from Slime Mould Algorithm|website=www.spacetelescope.org}}</ref>]]
The organization of structure arguably begins at the stellar level, though most cosmologists rarely address [[astrophysics]] on that scale. [[Star]]s are organized into [[galaxy|galaxies]], which in turn form [[galaxy group]]s, [[galaxy cluster]]s, [[supercluster]]s, sheets, [[galaxy filament|walls and filaments]], which are separated by immense [[void (astronomy)|voids]], creating a vast foam-like structure<ref>{{Cite book|url=https://books.google.com/books?id=RLwangEACAAJ|title=An Introduction to Modern Astrophysics|last1=Carroll|first1=Bradley W.|last2=Ostlie|first2=Dale A.|year=2013|publisher=Pearson|isbn=978-1292022932|edition=International|pages=1173–1174|language=en}}</ref> sometimes called the "cosmic web". Prior to 1989, it was commonly assumed that [[virial theorem|virialized]] galaxy clusters were the largest structures in existence, and that they were distributed more or less uniformly throughout the universe in every direction. However, since the early 1980s, more and more structures have been discovered. In 1983, Adrian Webster identified the [[Webster LQG]], a [[large quasar group]] consisting of 5 quasars. The discovery was the first identification of a large-scale structure, and has expanded the information about the known grouping of matter in the universe.

In 1987, [[R. Brent Tully|Robert Brent Tully]] identified the [[Pisces–Cetus Supercluster Complex]], the galaxy filament in which the [[Milky Way]] resides. It is about 1 billion light-years across. That same year, an unusually large region with a much lower than average distribution of galaxies was discovered, the [[Giant Void]], which measures 1.3 billion light-years across. Based on [[redshift survey]] data, in 1989 [[Margaret Geller]] and [[John Huchra]] discovered the "[[CfA2 Great Wall|Great Wall]]",<ref name="redshift">{{cite journal |author=Geller |first1=M. J. |last2=Huchra |first2=J. P. |date=1989 |title=Mapping the universe. |journal=Science |volume=246 |issue=4932 |pages=897–903 |bibcode=1989Sci...246..897G |doi=10.1126/science.246.4932.897 |pmid=17812575 |s2cid=31328798}}</ref> a sheet of galaxies more than 500 million [[light-year]]s long and 200 million light-years wide, but only 15 million light-years thick. The existence of this structure escaped notice for so long because it requires locating the position of galaxies in three dimensions, which involves combining location information about the galaxies with distance information from [[redshift]]s.

Two years later, astronomers Roger G. Clowes and Luis E. Campusano discovered the [[Clowes–Campusano LQG]], a [[large quasar group]] measuring two billion light-years at its widest point, which was the largest known structure in the universe at the time of its announcement. In April 2003, another large-scale structure was discovered, the [[Sloan Great Wall]]. In August 2007, a possible supervoid was detected in the constellation [[Eridanus (constellation)|Eridanus]].<ref>{{Cite web |title=Biggest void in space is 1 billion light years across |url=https://www.newscientist.com/article/dn12546-biggest-void-in-space-is-1-billion-light-years-across/ |access-date=2023-09-15 |website=New Scientist |language=en-US}}</ref> It coincides with the '[[CMB cold spot]]', a cold region in the microwave sky that is highly improbable under the currently favored cosmological model. This supervoid could cause the cold spot, but to do so it would have to be improbably big, possibly a billion light-years across, almost as big as the Giant Void mentioned above.

{{unsolved|physics|The largest structures in the universe are larger than expected. Are these actual structures or random density fluctuations?}}

[[File:Large-scale structure of light distribution in the universe.jpg|thumb|upright=2|Computer simulated image of an area of space more than 50 million light-years across, presenting a possible large-scale distribution of light sources in the universe—precise relative contributions of galaxies and [[quasar]]s are unclear.]]
Another large-scale structure is the [[SSA22 Protocluster]], a collection of galaxies and enormous gas bubbles that measures about 200 million light-years across.

In 2011, a large quasar group was discovered, [[U1.11]], measuring about 2.5 billion light-years across. On January 11, 2013, another large quasar group, the [[Huge-LQG]], was discovered, which was measured to be four billion light-years across, the largest known structure in the universe at that time.<ref>{{cite web | last = Wall | first = Mike | url = https://www.foxnews.com/science/largest-structure-in-universe-discovered/ | title = Largest structure in universe discovered | date = 2013-01-11 | publisher = [[Fox News]]}}</ref> In November 2013, astronomers discovered the [[Hercules–Corona Borealis Great Wall]],<ref name="2014paper">{{cite journal |last1=Horváth |first1=I. |last2=Hakkila |first2=Jon |last3=Bagoly |first3=Z. |date=2014 |title=Possible structure in the GRB sky distribution at redshift two |journal=Astronomy & Astrophysics |volume=561 |pages=L12 |arxiv=1401.0533 |bibcode=2014A&A...561L..12H |doi=10.1051/0004-6361/201323020 |s2cid=24224684}}</ref><ref name=original>{{cite arXiv |last1 = Horvath |first1 = I. |last2= Hakkila |first2=J. |last3=Bagoly |first3=Z. |title = The largest structure of the Universe, defined by Gamma-Ray Bursts |date = 2013 |eprint=1311.1104 |class=astro-ph.CO}}</ref> an even bigger structure twice as large as the former. It was defined by the mapping of [[gamma-ray burst]]s.<ref name=2014paper/><ref>{{cite web | last = Klotz | first = Irene | url = http://news.discovery.com/space/galaxies/universes-largest-structure-is-a-cosmic-conundrum-131119.htm | title = Universe's Largest Structure is a Cosmic Conundrum | date = 2013-11-19 | work = Discovery | access-date = 2013-11-20 | archive-date = 2016-05-16 | archive-url = https://web.archive.org/web/20160516172545/http://news.discovery.com/space/galaxies/universes-largest-structure-is-a-cosmic-conundrum-131119.htm | url-status = dead }}</ref>

In 2021, the [[American Astronomical Society]] announced the detection of the [[The Giant Arc|Giant Arc]]; a crescent-shaped string of galaxies that span 3.3 billion light years in length, located 9.2 billion light years from Earth in the constellation [[Boötes]] from observations captured by the [[Sloan Digital Sky Survey]].<ref>{{cite web | last = Ferreira | first = Becky | url = https://www.vice.com/en/article/a-structure-in-deep-space-is-so-giant-its-challenging-standard-physics/ | title = A Structure In Deep Space Is So Giant It's Challenging Standard Physics | date = 2021-06-23 | work = Vice}}</ref>