Interacting galaxy
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[[Image:Ssc2005-03b.jpg|thumb|285px|right|An artist's impression of '''interacting galaxies''']]
'''Interacting galaxies''' ('''''Colliding galaxies''''') are the result of one [[galaxy]]'s [[gravity]] disturbing another galaxy. An example of minor interaction is a [[satellite galaxy]] disturbing the primary galaxy's [[spiral arm]]s. An example of major interaction is a galactic collision.
==Satellite interaction==
[[Image:Whirlpool (M51).jpg|thumb|240px|right|The [[Whirlpool Galaxy]] with its [[satellite galaxy|satellite]] [[Irregular Galaxy NGC 5195|NGC 5195]]]]
A giant galaxy interacting with its [[satellite galaxy|satellites]] is common. A satellite's gravity could attract one of the primary's [[spiral arm]]s. Or even the satellite could dive in to the primary (e.g. [[Sagittarius Dwarf Elliptical Galaxy]]). This could trigger a small amount of [[star formation]]. The satellite could be a [[vacuum cleaner]] and suck up some of its primary's stars or [[vice versa]].
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==Galaxy collision==
[[Image:NGC4676.jpg|thumb|265px|right|The [[Mice Galaxies]]]]
Colliding galaxies are common in galaxy evolution. Due to the extremely tenuous distribution of matter in galaxies, these are not collisions in the normal sense of the word, but rather gravitational interaction. Colliding may lead to [[Galaxy merger|merging]]. This occurs when two galaxies collide and do not have enough momentum to continue traveling after the collision. Instead, they fall back into each other and eventually merge after many passes through each other, forming one galaxy. If one of the colliding galaxies is much larger than the other, it will remain largely intact after the merger; that is, the larger galaxy will look much the same while the smaller galaxy will be stripped apart and become part of the larger galaxy. Through-passes are less disruptive of galaxy shapes than mergers in that both galaxies largely retain their material and shape after the pass.
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==Galactic cannibalism==<!-- This section is linked from [[Galaxy]] -->
'''Galactic cannibalism''' refers to the process by which a large [[galaxy]], through [[galactic tide|tidal]] gravitational interactions with a companion, merges with that companion, resulting in a larger, often [[irregular galaxy]].
The most common result of the gravitational merger of two or more galaxies is an irregular galaxy of one form or another, although [[elliptical galaxy|elliptical galaxies]] may also result.
It has been suggested that galactic cannibalism is currently occurring between the [[Milky Way]] and the [[Magellanic clouds|Large and Small Magellanic Clouds]]. Streams of gravitationally-attracted [[hydrogen]] arcing from these dwarf galaxies to the Milky Way is taken as evidence for this theory.
== Notable interacting galaxies==
{| class="wikitable" style="text-align:center;border-collapse:collapse;" cellpadding="2"
|-
! style="background:#efefef;"| Name
! style="background:#efefef;"| [[Galaxy morphological classification|Type]]
! style="background:#efefef;"| Distance<br>(million [[light-years|ly]])
! style="background:#efefef;"| [[Apparent magnitude|Magnitude]]
! style="background:#efefef;"| Notes
|-
| [[Whirlpool Galaxy]] (M51)
| SAc (SB0-a)
| 37
| +8.4
| Satellite interacting<br>with its primary
|-
| [[NGC 2207 and IC 2163]]
| SAc/SAbc
| 114
| +11
| galaxies going through the<br>'''first phase''' in galactic collision
|-
| [[Mice Galaxies]]<br>(IC 819/20)
| S0/SB(s)ab
| 300
| +13.5
| galaxies going through the<br>'''second phase''' in galactic collision
|-
| [[NGC 1097]]
| SB(s)bc (E6)
| 45
| +9.5
| Satellite interacting<br>with its primary
|-
| [[Antennae Galaxies]]<br>(NGC 4038/9)
| SAc/SBm
| 68
| +10.3
| galaxies going through the<br>'''third phase''' in galactic collision
|-
| [[NGC 520]]
| S
| 100
| +11.3
| galaxies going through the<br>'''third phase''' in galactic collision
|}
==Future collision of the Milky Way Galaxy with the Andromeda Galaxy==
{{main|Andromeda-Milky Way collision}}
[[Astronomer]]s have estimated that our galaxy, the [[Milky Way galaxy]], will collide with the [[Andromeda galaxy]] in about three billion years. It is thought that the two [[Spiral galaxy|spiral galaxies]] will merge to become an [[elliptical galaxy]].
== See also ==
*[[Galactic tide]]
*[[Galaxy merger]]
*[[NGC 7318]]
<!--==References==
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*Link: http://en.wikipedia.org/wiki/Whirlpool_Galaxy
==External links==
{{Commonscat|Interacting galaxies}}
*[http://www.public.iastate.edu/~curt/cg/homepage.html Galaxy Collisions]
*[http://www.iac.es/gabinete/noticias/2001/mar08i.htm Galactic cannibalism]
*[http://burro.cwru.edu/JavaLab/GalCrashWeb/ Galactic Collision Simulation]
[[Category:Interacting galaxies| ]]
[[Category:Extragalactic astronomy]]
[[ca:Interacció de galàxies]]
[[de:Wechselwirkende Galaxien]]
[[fr:Interaction de galaxies]]
[[it:Galassie interagenti]]
[[lv:Mijiedarbojošās galaktikas]]
[[lb:Wiesselwierkend Galaxien]]
[[pl:Zderzenie galaktyk]]
[[sk:Interagujúca galaxia]]