Editing Galaxy (section)

=== Interacting ===
{{Main|Interacting galaxy}}
[[File:Antennae galaxies xl.jpg|thumb|right|200px|The [[Antennae Galaxies]] are undergoing a collision that will result in their eventual merger.]]

Interactions between galaxies are relatively frequent, and they can play an important role in [[galaxy formation and evolution|galactic evolution]]. Near misses between galaxies result in warping distortions due to [[galactic tide|tidal interactions]], and may cause some exchange of gas and dust.<ref name="umda">{{cite web
 |url=http://www.astro.umd.edu/education/astro/gal/interact.html
 |title=Galaxy Interactions
 |publisher=[[University of Maryland]] Department of Astronomy
 |access-date=December 19, 2006
 |archive-url=https://web.archive.org/web/20060509074300/http://www.astro.umd.edu/education/astro/gal/interact.html
 |archive-date=May 9, 2006
}}</ref><ref name="suia">{{cite web
 |title=Interacting Galaxies
|url=http://cosmos.swin.edu.au/entries/interactinggalaxies/interactinggalaxies.html?e=1
 |publisher=[[Swinburne University]]
 |access-date=December 19, 2006
 |archive-date=April 18, 2023
 |archive-url=https://web.archive.org/web/20230418184032/https://astronomy.swin.edu.au/cosmos/I/Interacting+Galaxies
 |url-status=live
 }}</ref>
Collisions occur when two galaxies pass directly through each other and have sufficient relative momentum not to merge. The stars of interacting galaxies usually do not collide, but the gas and dust within the two forms interacts, sometimes triggering star formation. A collision can severely distort the galaxies' shapes, forming bars, rings or tail-like structures.<ref name="umda" /><ref name="suia" />

At the extreme of interactions are galactic mergers, where the galaxies' relative momentums are insufficient to allow them to pass through each other. Instead, they gradually merge to form a single, larger galaxy. Mergers can result in significant changes to the galaxies' original morphology. If one of the galaxies is much more massive than the other, the result is known as [[Interacting galaxy#Galactic cannibalism|cannibalism]], where the more massive larger galaxy remains relatively undisturbed, and the smaller one is torn apart. The Milky Way galaxy is currently in the process of cannibalizing the [[Sagittarius Dwarf Elliptical Galaxy]] and the [[Canis Major Dwarf Galaxy]].<ref name="umda" /><ref name="suia" />