Editing M81 Group (section)

==Interactions within the group==

Messier 81, Messier 82, and NGC 3077 are all strongly [[interacting galaxy|interacting]] with each other.<ref name="yunetal1994">{{cite journal
  | author=M. S. Yun
  | author2=P. T. P. Ho
  | author3=K. Y. Lo
  | title=A high-resolution image of atomic hydrogen in the M81 group of galaxies
  | journal=Nature
  | date=1994
  | volume=372
  | pages=530–532
  | bibcode=1994Natur.372..530Y | doi = 10.1038/372530a0
  | pmid=7990925
  | issue=6506
| s2cid=4369085
 }}</ref>  Observations of the 21-centimeter [[hydrogen line]] indicate how the galaxies are connected.<ref name="chynowethetal2008">{{cite journal 
|last1=Chynoweth 
|first1=Katie M. 
 |display-authors=etal 
|title=Neutral Hydrogen Clouds in the M81/M82 Group 
|journal=The Astronomical Journal 
|date=2008 
|volume=135 
|issue=2008 June 
|pages=1983–1992 
|doi=10.1088/0004-6256/135/6/1983|arxiv=0803.3631 
|bibcode=2008AJ....135.1983C 
 |s2cid=4490764 
 }}</ref> 
The gravitational interactions have stripped some [[hydrogen]] gas away from all three galaxies, leading to the formation of filamentary gas structures within the group.<ref name="yunetal1994" />  Bridges of neutral hydrogen have been shown to connect M81 with M82 and NGC 3077.<ref name="chynowethetal2008" /><ref name="hulst1978">{{cite journal |last1=Hulst 
|first1=J. M. van der 
|title=The Structure and Kinematics of the Neutral Hydrogen Bridge Between M 81 and NGC 3077 
|journal=Astronomy and Astrophysics 
|date=1978 
|volume=75 
|issue=1–2 
|pages=97–111}}</ref> Moreover, the interactions have also caused some [[interstellar medium|interstellar gas]] to fall into the centers of Messier 82 and NGC 3077, which has led to strong [[starburst galaxy|starburst activity]] (or the formation of many stars) within the centers of these two galaxies.<ref name="yunetal1994" /> Computer simulations of [[tidal forces|tidal interactions]] have been used to show how the current structure of the group could have been created.<ref name="yun1999">{{cite book 
|last1=Yun |first1=M. S. 
|chapter=Tidal Interactions in M81 Group 
|title=Galaxy Interactions at Low and High Redshift 
|date=1999 
|volume=186 
|page=81 
|doi=10.1007/978-94-011-4665-4_18 
|bibcode=1999IAUS..186...81Y 
|isbn=978-0-7923-5833-6 
|ref=1999IAUS..186...81Y}}</ref>