Interacting galaxies (''colliding galaxies'') are

galaxies A galaxy is a system of stars, stellar remnants, interstellar gas, dust, dark matter, bound together by gravity. The word is derived from the Greek ' (), literally 'milky', a reference to the Milky Way galaxy that contains the Solar System ...

whose gravitational fields result in a disturbance of one another. An example of a minor interaction is a satellite galaxy disturbing the primary galaxy's

spiral arm Spiral galaxies form a class of galaxy originally described by Edwin Hubble in his 1936 work ''The Realm of the Nebulae''galaxy merger Galaxy mergers can occur when two (or more) galaxies collide. They are the most violent type of galaxy interaction. The gravitational interactions between galaxies and the friction between the gas and dust have major effects on the galaxies ...

Satellite interaction

A giant galaxy interacting with its

satellites A satellite or artificial satellite is an object intentionally placed into orbit in outer space. Except for passive satellites, most satellites have an electricity generation system for equipment on board, such as solar panels or radioisotop ...

is common. A satellite's gravity could attract one of the primary's

spiral arm Spiral galaxies form a class of galaxy originally described by Edwin Hubble in his 1936 work ''The Realm of the Nebulae''Sagittarius Dwarf Elliptical Galaxy diving into the

Milky Way The Milky Way is the galaxy that includes our Solar System, with the name describing the galaxy's appearance from Earth: a hazy band of light seen in the night sky formed from stars that cannot be individually distinguished by the naked eye. ...

. That can possibly trigger a small amount of

star formation Star formation is the process by which dense regions within molecular clouds in The "medium" is present further soon.-->interstellar space

. Such orphaned clusters of stars were sometimes referred to as "blue blobs" before they were recognized as stars.

Galaxy collision

Colliding galaxies are common during galaxy evolution. The extremely tenuous distribution of matter in galaxies means these are not collisions in the traditional sense of the word, but rather gravitational interactions. Colliding may lead to merging if two galaxies collide and do not have enough momentum to continue traveling after the collision. As with other galaxy collisions, the merging of two galaxies may create a starburst region of new stars. In that case, they fall back into each other and eventually merge into one galaxy after many passes through each other. If one of the colliding galaxies is much larger than the other, it will remain largely intact after the merger. The larger galaxy will look much the same, while the smaller galaxy will be stripped apart and become part of the larger galaxy. When galaxies pass through each other, unlike during mergers, they largely retain their material and shape after the pass. Galactic collisions are now frequently simulated on computers, which use 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 GALME
27 March 2010
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Gallery

File:Galactic Creatures at Play.jpg, UGC 2369 taken by HST. File:Close encounter IRAS 06076-2139.jpg, Close encounter at IRAS 06076-2139. File:NGC 4298 and NGC 4302 - Heic1709a.jpg, Interacting galaxies NGC 4302 and NGC 4298 both located 55 million light-years away. File:NGC 6052.jpg, Galaxy NGC 6052 merging into a single structure. File:Galactic soup.jpg, Galaxy pair Zw I 136. File:The messy result of a galactic collision.jpg,

ESO 576-69 The European Organisation for Astronomical Research in the Southern Hemisphere, commonly referred to as the European Southern Observatory (ESO), is an intergovernmental research organisation made up of 16 member states for ground-based ast ...

is believed to be the nucleus of a former spiral galaxy. File:Whirlpool (M51).jpg, The Whirlpool Galaxy with its

satellite A satellite or artificial satellite is an object intentionally placed into orbit in outer space. Except for passive satellites, most satellites have an electricity generation system for equipment on board, such as solar panels or radioiso ...

NGC 5195. File:NGC4676.jpg, The Mice Galaxies. File:Colliding Galaxies Create Active Galactic Nuclei.OGG, This simulation follows the collision of two spiral galaxies that harbour giant black holes. File:Defying cosmic convention.jpg, NGC 3447 comprises a couple of interacting galaxies. File:NGC 1510 and NGC 1512 in UV Light.jpg,

Barred spiral galaxy A barred spiral galaxy is a spiral galaxy with a central bar-shaped structure composed of stars. Bars are found in about two thirds of all spiral galaxies, and generally affect both the motions of stars and interstellar gas within spiral galaxies ...

NGC 1512 NGC 1512 is a barred spiral galaxy approximately 38 million light-years away from Earth in the constellation Horologium. The galaxy displays a double ring structure, with a (nuclear) ring around the galactic nucleus and an (inner) further out ...

in the process of a lengthy merger with

dwarf Dwarf or dwarves may refer to: Common uses *Dwarf (folklore), a being from Germanic mythology and folklore * Dwarf, a person or animal with dwarfism Arts, entertainment, and media Fictional entities * Dwarf (''Dungeons & Dragons''), a humanoid ...

elliptical galaxy An elliptical galaxy is a type of galaxy with an approximately ellipsoidal shape and a smooth, nearly featureless image. They are one of the four main classes of galaxy described by Edwin Hubble in his Hubble sequence and 1936 work ''The Real ...

NGC 1510 NGC 1510 is a dwarf lenticular galaxy approximately 38 million light-years away from Earth in the constellation of Horologium. It was discovered by John Herschel on December 4, 1836. Gravitational interaction with NGC 1512 NGC 1510 is under ...

. File:Hubble Interacting Galaxy ESO 593-8 (2008-04-24).jpg, ESO 593-8 is an impressive pair of interacting galaxies with a feather-like galaxy crossing a companion galaxy.

Galactic cannibalism

Galactic cannibalism is a common phenomenon that occurs in the universe, which refers to the process in which a large

galaxy A galaxy is a system of stars, stellar remnants, interstellar gas, dust, dark matter, bound together by gravity. The word is derived from the Greek ' (), literally 'milky', a reference to the Milky Way galaxy that contains the Solar System ...

, through tidal gravitational interactions with a companion, merges with that companion; that results in a larger, often irregular galaxy. The most common result of the gravitational merger between two or more galaxies is an irregular galaxy, but elliptical galaxies may also result. It has been suggested that galactic cannibalism is currently occurring between the

and the Large and Small Magellanic Clouds. Streams of gravitationally-attracted

hydrogen Hydrogen is the chemical element with the symbol H and atomic number 1. Hydrogen is the lightest element. At standard conditions hydrogen is a gas of diatomic molecules having the formula . It is colorless, odorless, tasteless, non-to ...

arcing from these dwarf galaxies to the Milky Way is taken as evidence for the 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 cluster A galaxy cluster, or a cluster of galaxies, is a structure that consists of anywhere from hundreds to thousands of galaxies that are bound together by gravity, with typical masses ranging from 1014 to 1015 solar masses. They are the second-lar ...

s, such as

Virgo Virgo may refer to: *Virgo (astrology), the sixth astrological sign of the zodiac * Virgo (constellation), a constellation *Virgo Cluster, a cluster of galaxies in the constellation Virgo *Virgo Stellar Stream, remains of a dwarf galaxy * Virgo Su ...

and

Coma A coma is a deep state of prolonged unconsciousness in which a person cannot be awakened, fails to respond normally to painful stimuli, light, or sound, lacks a normal wake-sleep cycle and does not initiate voluntary actions. Coma patients exhi ...

, where galaxies are moving at high relative speeds and suffering frequent encounters with other systems of the cluster by the high galactic density of the latter. According to

computer simulation Computer simulation is the process of mathematical modelling, performed on a computer, which is designed to predict the behaviour of, or the outcome of, a real-world or physical system. The reliability of some mathematical models can be deter ...

s, the interactions convert the affected galaxy disks into disturbed

barred spiral galaxies A barred spiral galaxy is a spiral galaxy with a central bar-shaped structure composed of stars. Bars are found in about two thirds of all spiral galaxies, and generally affect both the motions of stars and interstellar gas within spiral galaxie ...

and produces starbursts followed by, if more encounters occur, loss of

angular momentum In physics, angular momentum (rarely, moment of momentum or rotational momentum) is the rotational analog of linear momentum. It is an important physical quantity because it is a conserved quantity—the total angular momentum of a closed syst ...

and heating of their gas. The result would be the conversion of (late type) low-luminosity spiral galaxies into dwarf spheroidals and dwarf ellipticals. Evidence for the hypothesis had been claimed by studying early-type dwarf galaxies in the Virgo Cluster and finding structures, such as disks and spiral arms, which suggest they are former disk systems transformed by the above-mentioned interactions. However, the existence of similar structures in isolated early-type dwarf galaxies, such as

LEDA 2108986 LEDA 2108986, also known by its Case Western Reserve University designation "Case Galaxy 611" (CG 611), is an extremely isolated, early-type dwarf galaxy with an embedded spiral structure residing in what is likely an intermediate-scale disk. T ...

, has undermined this hypothesis

Notable interacting galaxies

Future collision of the Milky Way with Andromeda

Astronomers have estimated the

Milky Way Galaxy The Milky Way is the galaxy that includes our Solar System, with the name describing the galaxy's appearance from Earth: a hazy band of light seen in the night sky formed from stars that cannot be individually distinguished by the naked eye. ...

will collide with the

Andromeda Galaxy The Andromeda Galaxy (IPA: ), also known as Messier 31, M31, or NGC 224 and originally the Andromeda Nebula, is a barred spiral galaxy with the diameter of about approximately from Earth and the nearest large galaxy to the Milky Way. The gal ...

in about 4.5 billion years. It is thought that the two spiral galaxies will eventually merge to become an

whose gravitational interactions will fling various celestial bodies outward, evicting them from the resulting elliptical galaxy.

Astronomy Astronomy () is a natural science that studies celestial objects and phenomena. It uses mathematics, physics, and chemistry in order to explain their origin and evolution. Objects of interest include planets, moons, stars, nebulae, g ...

, June 2008, page 28, by Abraham Loeb and T.J.Cox or perhaps a large disk galaxy.

References

External links

Galaxy CollisionsGalactic Collision SimulationGALMER: Galaxy Merger Simulations
{{DEFAULTSORT:Interacting Galaxy Extragalactic astronomy Articles containing video clips