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Interacting galaxy

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Subject: Galaxy merger, Polar-ring galaxy, Galactic tide, Mayall's Object, NGC 428
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Interacting galaxy

NGC 3169 (left) and NGC 3166 (right) display some curious features, demonstrating that each member of the duo is close enough to feel the distorting gravitational influence of the other. Iimage from the Wide Field Imager on the MPG/ESO 2.2-metre telescope at the La Silla Observatory.

Interacting galaxies (colliding galaxies) are galaxies whose gravitational fields result in a disturbance of one another. An example of a minor interaction is a satellite galaxy's disturbing the primary galaxy's spiral arms. An example of a major interaction is a galactic collision.


  • Satellite interaction 1
  • Galaxy collision 2
  • Galactic cannibalism 3
  • Galaxy harassment 4
  • Notable interacting galaxies 5
  • Future collision of the Milky Way with Andromeda 6
  • See also 7
  • References 8
  • External links 9

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 the secondary satellite's path could coincide with the position of the primary satellite's and thus, would it 'dive' into the primary galaxy (the Sagittarius Dwarf Elliptical Galaxy into the Milky Way being an example of the latter ). This can possibly trigger a small amount of star formation.

Galaxy collision

Merging galaxies in the distant Universe through a gravitational magnifying glass.[1]

Colliding galaxies are common in galaxy evolution. [2] 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 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.

Galactic collisions are now frequently simulated on computers, which take into account realistic physics principles including the simulation of gravitational forces, gas dissipation phenomena, star formation and feedback. Dynamical friction slows the relative motion galaxy pairs, which may possibly merge at some point, according to the initial relative energy of the orbits. A library of simulated galaxy collisions can be found at the Paris Observatory website: GALMER [3]

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 between two or more galaxies is an irregular galaxy, 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.

Galaxy harassment

Galaxy harassment is a type of interaction between a low-luminosity galaxy and a brighter one that takes place within rich galaxy clusters such as Virgo and Coma, where galaxies are moving at high relative speeds and suffering frequent encounters with other systems of the cluster due to the high galactic density of the latter. According to computer simulations, these interactions convert the affected systems into disturbed barred spiral galaxies and produces starbursts on them followed, if more encounters occur, by loss of angular momentum and heating of their gas. Their result would be the conversion of (late type) low-luminosity spiral galaxies into dwarf spheroidals and dwarf ellipticals.[6]

Evidence for this hypothesis has been found studying early-type dwarf galaxies of the Virgo Cluster and finding on them structures such as disks and spiral arms suggesting they are former disk systems transformed by the mentioned interactions.[7]

Notable interacting galaxies

Name Type Distance
(million ly)
Magnitude Notes
Milky Way Galaxy, LMC and SMC SBc/SB(s)m/SB(s)m pec 0 Satellites interacting with their primary
Whirlpool Galaxy (M51) SAc (SB0-a) 37 +8.4 Satellite interacting with its primary
NGC 1097 SB(s)bc (E6) 45 +9.5 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 (NGC 4676A and NGC 4676B) S0/SB(s)ab 300 +13.5 galaxies going through the second phase in galactic collision
Antennae Galaxies (NGC 4038/9) SAc/SBm 45 +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

Future collision of the Milky Way with Andromeda

Astronomers have estimated that our galaxy, the Milky Way galaxy, will collide with the Andromeda galaxy in about 4.5 billion years. It is thought that the two spiral galaxies will eventually merge to become an elliptical galaxy[8][9] or perhaps a large disk galaxy.[10]

See also


  1. ^ "Best View Yet of Merging Galaxies in Distant Universe". ESO Press Release. Retrieved 26 August 2014. 
  2. ^ 2015-04-21 How the Hubble Space Telescope Changed Our View of the Cosmos-Galactic Collisions Photographs
  3. ^ GALMER 27 March 2010
  4. ^ "Galactic soup". ESA/Hubble Picture of the Week. Retrieved 18 August 2014. 
  5. ^ "The messy result of a galactic collision". ESA/Hubble Picture of the Week. Retrieved 29 May 2013. 
  6. ^ Galaxy Harassment
  7. ^ More evidence for hidden spiral and bar features in bright early-type dwarf galaxies
  8. ^ whose gravitational interactions will fling various celestial bodies outward; 'evicting' them from the resulting elliptical galaxy.
  9. ^ Astronomy, June 2008, page 28, by Abraham Loeb and T.J.Cox
  10. ^ Junko Ueda; et al. "Cold molecular gas in merger remnants. I. Formation of molecular gas disks". The Astrophysical Journal Supplement Series 214 (1).  

External links

  • Galaxy Collisions
  • Galactic cannibalism
  • Galactic Collision Simulation
  • GALMER: Galaxy Merger Simulations
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