Interacting galaxy
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- See also: Galactic tide
- See also: Galaxy merger
Interacting galaxies (Colliding galaxies) is the result of one galaxy's gravity disturbing another galaxy. An example of minor interaction would be a satellite galaxy disturbing the primary galaxy's spiral arms. An example of major interaction would be a galactic collision.
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[edit] Satellite interaction
A giant galaxy interacting with its satellites is common. A satellite's gravity could attract one of the primary's spiral arms. 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.
[edit] Galaxy collision
Colliding galaxies are common in galaxy evolution. Colliding may lead to merging. Merging is the most violent of all galaxy interactions. 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 together, 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. Collisions are less violent than mergers in that both galaxies remain separate after the collisions.
[edit] Galactic cannibalism
Galactic cannibalism refers to the process by which a large galaxy, through 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 galaxies may also result.
It has been suggested that galactic cannibalism is currently occurring between the Milky Way and the 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.
[edit] Notable interacting galaxies
| Name | Type | Distance (million ly) |
Magnitude | Notes |
|---|---|---|---|---|
| Whirlpool Galaxy (M51) | SAc (SB0-a) | 37 | +8.4 | Satellite interacting with its primary |
| NGC 2207 and IC 2163 | SAc/SAbc | 114 | +11 | galaxies going through the first phase in galactic collision |
| Mice Galaxies (IC 819/20) |
S0/SB(s)ab | 300 | +13.5 | galaxies going through the second phase in galactic collision |
| NGC 1097 | SB(s)bc (E6) | 45 | +9.5 | Satellite interacting with its primary |
| Antennae Galaxies (NGC 4038/9) |
SAc/SBm | 68 | +10.3 | galaxies going through the third phase in galactic collision |
| NGC 520 | S | 100 | +11.3 | galaxies going through the third phase in galactic collision |
