Editing Galaxy groups and clusters (section)

== Groups of galaxies ==
{{main|Galaxy group}}
[[File:Map of the positions of thousands of galaxies in the VIPERS survey.jpg|thumb|Map of the positions of thousands of galaxies in the VIPERS survey<ref>{{cite news|title=Huge Map of the Distant Universe Reaches Halfway Point|url=http://www.eso.org/public/announcements/ann13022/|access-date=2 April 2013|newspaper=ESO}}</ref>]]

Groups of [[Galaxy|galaxies]] are the smallest aggregates of galaxies. They typically contain no more than 50 galaxies in a diameter of 1 to 2 [[Parsec#Megaparsecs and gigaparsecs|megaparsecs]] (Mpc)(see [[1 E22 m|10<sup>22</sup> m]] for distance comparisons). Their mass is approximately 10<sup>13</sup> [[solar mass]]es. The spread of velocities for the individual galaxies is about 150&nbsp;km/s. However, this definition should be used as a guide only, as larger and more massive galaxy systems are sometimes classified as galaxy groups.<ref>{{cite web|url=http://csep10.phys.utk.edu/astr162/lect/gclusters/groups.html|title=Groups of Galaxies|publisher=University of Tennessee, Knoville|author=UTK Physics Dept|access-date=September 27, 2012}}</ref> Groups are the most common structures of galaxies in the universe, comprising at least 50% of the galaxies in the local universe. Groups have a mass range between those of the very large [[Elliptical galaxy|elliptical galaxies]] and clusters of galaxies.<ref name=2013A&A...552A..80M>{{cite journal |title= Dynamical analysis of strong-lensing galaxy groups at intermediate redshift |author= Muñoz, R. P. |display-authors= etal |date= 11 December 2012 |publication-date= April 2013 |journal= Astronomy & Astrophysics |volume= 552 |id= A80 |page= 18 |arxiv= 1212.2624 |doi= 10.1051/0004-6361/201118513 |bibcode= 2013A&A...552A..80M |s2cid= 17865754 }}</ref>

Our own galaxy, the [[Milky Way]], is contained in the [[Local Group]] of more than 54 galaxies.<ref>{{cite web|title=The Local Group|url=http://www.ast.cam.ac.uk/~mike/local_more.html|author=Mike Irwin|access-date=2009-11-07|archive-date=2019-06-19|archive-url=https://web.archive.org/web/20190619131606/https://www.ast.cam.ac.uk/~mike/local_more.html|url-status=dead}}</ref>

In July 2017 S. Paul, R. S. John et al. defined clear distinguishing parameters for classifying galaxy aggregations as ‘galaxy groups’ and ‘clusters’ on the basis of scaling laws that they followed.<ref>{{cite journal|title=Understanding 'galaxy groups' as a unique structure in the universe|journal = Monthly Notices of the Royal Astronomical Society|volume = 471|issue = 1|pages = 2–11|author=S. Paul|author2=R. S. John|author3=P. Gupta|author4= H. Kumar|doi = 10.1093/mnras/stx1488|year = 2017| doi-access=free |bibcode = 2017MNRAS.471....2P|arxiv = 1706.01916}}</ref> According to this paper, galaxy aggregations less massive than 8 × 10<sup>13</sup> [[solar mass]]es are classified as galaxy groups.