Interacting galaxy
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Interacting galaxies (''colliding galaxies'') are
galaxies A galaxy is a system of stars, stellar remnants, interstellar gas, dust, and 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 Sys ...
whose gravitational fields result in a disturbance of one another. Major mergers occur between galaxies with similar amounts of mass, whereas minor mergers involve galaxies with masses that vary significantly. An example of a minor interaction is a
satellite galaxy A satellite galaxy is a smaller companion galaxy that travels on bound orbits within the gravitational potential of a more massive and Luminosity, luminous host galaxy (also known as the primary galaxy). Satellite galaxies and their constituents ...
disturbing the primary galaxy's
spiral arm Spiral arms are a defining feature of spiral galaxies. They manifest as spiral-shaped regions of enhanced brightness within the galactic disc. Typically, spiral galaxies exhibit two or more spiral arms. The collective configuration of these arms i ...
s. An example of a major interaction is a galactic collision, which may lead to a
galaxy merger Galaxy mergers can occur when two (or more) Galaxy, galaxies collide. They are the most violent type of Interacting galaxy, galaxy interaction. The Gravitation, gravitational interactions between galaxies and the friction between the gas and Cosmi ...
.


Satellite interaction

A giant galaxy interacting with its
satellites A satellite or an artificial satellite is an object, typically a spacecraft, placed into orbit around a celestial body. They have a variety of uses, including communication relay, weather forecasting, navigation ( GPS), broadcasting, scientif ...
is common. A satellite's gravity could attract one of the primary's
spiral arm Spiral arms are a defining feature of spiral galaxies. They manifest as spiral-shaped regions of enhanced brightness within the galactic disc. Typically, spiral galaxies exhibit two or more spiral arms. The collective configuration of these arms i ...
s. Alternatively, the secondary satellite can dive into the primary galaxy, as in the Sagittarius Dwarf Elliptical Galaxy diving into the
Milky Way The Milky Way or Milky Way Galaxy is the galaxy that includes the Solar System, with the name describing the #Appearance, galaxy's appearance from Earth: a hazy band of light seen in the night sky formed from stars in other arms of the galax ...
. That can possibly trigger a small amount of
star formation Star formation is the process by which dense regions within molecular clouds in interstellar space—sometimes referred to as "stellar nurseries" or "star-forming regions"—Jeans instability, collapse and form stars. As a branch of astronomy, sta ...
. 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. As a result, some galaxy features such as star formation, shape, and size are impacted by interactions with other galaxies. 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 A starburst region is a region of space that is undergoing a large amount of star formation. A starburst is an astrophysical process that involves star formation occurring at a rate that is large compared to the rate that is typically observed. Th ...
of new stars. This starburst is an example of an increased star formation rate within the merged galaxies. A study conducted in 2024 shows that a key component in determining this change in star formation rate is the masses of the two galaxies involved. It suggests that if the two galaxies are of similar mass to begin with, this increase in star formation rate will be greater. When a starburst region is created, the galaxies 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 of 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.


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. Clusters consist of galax ...
s, such as
Virgo Virgo may refer to: Arts and entertainment * Virgo (film), a 1970 Egyptian film * Virgo (character), several Marvel Comics characters * Virgo Asmita, a character in the manga ''Saint Seiya: The Lost Canvas'' * ''Virgo'' (album), by Virgo Four, ...
and
Coma A coma is a deep state of prolonged unconsciousness in which a person cannot be awakened, fails to Nociception, respond normally to Pain, painful stimuli, light, or sound, lacks a normal Circadian rhythm, sleep-wake cycle and does not initiate ...
, where galaxies are moving at high
relative speed The relative velocity of an object ''B'' relative to an observer ''A'', denoted \mathbf v_ (also \mathbf v_ or \mathbf v_), is the velocity vector (physics), vector of ''B'' measured in the rest frame of ''A''. The relative speed v_ = \, \mathb ...
s and suffering frequent encounters with other systems of the cluster due to the high galactic density. According to
computer simulation Computer simulation is the running of a mathematical model on a computer, the model being designed to represent the behaviour of, or the outcome of, a real-world or physical system. The reliability of some mathematical models can be determin ...
s, the interactions convert the affected galaxy disks into disturbed barred spiral galaxies and produces starbursts followed by, if more encounters occur, loss of
angular momentum Angular momentum (sometimes called moment of momentum or rotational momentum) is the rotational analog of Momentum, linear momentum. It is an important physical quantity because it is a Conservation law, conserved quantity – the total ang ...
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 disc systems transformed by the above-mentioned interactions. 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 examples


Andromeda–Milky Way collision

Astronomers have estimated the
Milky Way The Milky Way or Milky Way Galaxy is the galaxy that includes the Solar System, with the name describing the #Appearance, galaxy's appearance from Earth: a hazy band of light seen in the night sky formed from stars in other arms of the galax ...
Galaxy will collide with the
Andromeda Galaxy The Andromeda Galaxy is a barred spiral galaxy and is the nearest major galaxy to the Milky Way. It was originally named the Andromeda Nebula and is cataloged as Messier 31, M31, and NGC 224. Andromeda has a Galaxy#Isophotal diameter, D25 isop ...
in about 4.5 billion years. Thanks to the Hubble Space Telescope, astronomers were able to more accurately track Andromeda's movement, leading to the conclusion that the two galaxies will temporarily touch before eventually undergoing an ultimate merging. Some think the two spiral galaxies will eventually merge to become an
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 three main galaxy morphological classification, classes of galaxy described by Edwin Hubble in his Hub ...
whose gravitational interactions will fling various celestial bodies outward, evicting them from the resulting elliptical galaxy. or perhaps a large
disc galaxy A disc galaxy (or disk galaxy) is a galaxy characterized by a galactic disc. This is a flattened circular volume of stars that are mainly orbiting the galactic core in the same plane. These galaxies may or may not include a central non-disc-like ...
.


See also

* NGC 7318


References


External links


Galaxy CollisionsGALMER: Galaxy Merger Simulations
{{DEFAULTSORT:Interacting Galaxy Extragalactic astronomy Articles containing video clips