Editing Galaxy (section)

=== Dwarfs ===
{{Main|Dwarf galaxy}}

Despite the prominence of large elliptical and spiral galaxies, most galaxies are dwarf galaxies.<ref name=Mateo19989/> They are relatively small when compared with other galactic formations, being about one hundredth the size of the Milky Way, with only a few billion stars. [[Blue compact dwarf]] galaxies contains large clusters of [[OB star|young, hot, massive stars]]. Ultra-compact dwarf galaxies have been discovered that are only 100&nbsp;parsecs across.<ref>{{cite journal
 |last1=Phillipps |first1=S.
 |last2=Drinkwater |first2=M. J.
 |last3=Gregg |first3=M. D.
 |last4=Jones |first4=J. B.
 |s2cid=18297376
 |date=2001
 |title=Ultracompact Dwarf Galaxies in the Fornax Cluster
 |journal=[[The Astrophysical Journal]]
 |volume=560 |issue=1 |pages=201–206
 |bibcode=2001ApJ...560..201P
 |doi=10.1086/322517
|arxiv = astro-ph/0106377 }}</ref>

Many dwarf galaxies may orbit a single larger galaxy; the Milky Way has at least a dozen such satellites, with an estimated 300–500 yet to be discovered.<ref>{{cite magazine
 |last1=Groshong
 |first1=Kimm
 |date=April 24, 2006
 |title=Strange satellite galaxies revealed around Milky Way
 |magazine=[[New Scientist]]
 |url=https://www.newscientist.com/article/dn9043-strange-satellite-galaxies-revealed-around-milky-way.html
 |access-date=January 10, 2007
 |archive-date=July 2, 2015
 |archive-url=https://web.archive.org/web/20150702024442/http://www.newscientist.com/article/dn9043-strange-satellite-galaxies-revealed-around-milky-way.html
 |url-status=live
 }}</ref>
Most of the information we have about dwarf galaxies come from observations of the [[local group]], containing two spiral galaxies, the Milky Way and Andromeda, and many dwarf galaxies. These dwarf galaxies are classified as either [[irregular galaxy|irregular]] or [[dwarf elliptical galaxy|dwarf elliptical]]/[[dwarf spheroidal galaxy|dwarf spheroidal galaxies]].<ref name=Mateo19989>{{Cite journal |last=Mateo |first=Mario |date=1998 |title=Dwarf Galaxies of the Local Group |url=https://www.annualreviews.org/doi/10.1146/annurev.astro.36.1.435 |journal=[[Annual Review of Astronomy and Astrophysics]] |language=en |volume=36 |issue=1 |pages=435–506 |doi=10.1146/annurev.astro.36.1.435 |arxiv=astro-ph/9810070 |bibcode=1998ARA&A..36..435M |s2cid=119333888 |issn=0066-4146}}</ref>

A study of 27 Milky Way neighbors found that in all dwarf galaxies, the central mass is approximately 10 million [[solar mass]]es, regardless of whether it has thousands or millions of stars. This suggests that galaxies are largely formed by [[dark matter]], and that the minimum size may indicate a form of [[warm dark matter]] incapable of gravitational coalescence on a smaller scale.<ref>{{cite web
 |last1=Schirber
 |first1=M.
 |date=August 27, 2008
 |url=https://www.science.org/content/article/no-slimming-down-dwarf-galaxies
 |title=No Slimming Down for Dwarf Galaxies
 |publisher=[[ScienceNOW]]
 |access-date=August 27, 2008
 |archive-date=May 30, 2020
 |archive-url=https://web.archive.org/web/20200530044532/https://www.sciencemag.org/news/2008/08/no-slimming-down-dwarf-galaxies
 |url-status=live
 }}</ref>