Interacting galaxy
Encyclopedia
Interacting 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.
is common. A satellite's gravity could attract one of the primary's spiral arms. Or the satellite could dive in to the primary (e.g. Sagittarius Dwarf Elliptical Galaxy
). This could trigger a small amount of star formation
.
. 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.
Galaxy collisions are now frequently simulated on computers, with all
the realistic physics, including gravity forces, gas dissipation, star formation and feedback. Dynamical friction slows down galaxy pairs, which may or may not merge at some point, according to the initial relative energy of the orbits. A simulated library of galaxy collisions can be found at the Paris Observatory website: GALMER
, 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.
in about 4.5 billion years. It is thought that the two spiral galaxies
will merge to become an elliptical galaxy
.
Galaxy
A galaxy is a massive, gravitationally bound system that consists of stars and stellar remnants, an interstellar medium of gas and dust, and an important but poorly understood component tentatively dubbed dark matter. The word galaxy is derived from the Greek galaxias , literally "milky", a...
whose gravitational fields result in a disturbance of one another. An example of a minor interaction is a satellite galaxy
Satellite galaxy
A satellite galaxy orbits a larger galaxy due to gravitational attraction. Although a galaxy is made of a large number of objects which are not connected to each other, it has a center of mass, which represents a weighted average of the positions of each component object...
's disturbing the primary galaxy's spiral arms. An example of a major interaction is a galactic collision.
Satellite interaction
A giant galaxy interacting with its satellitesSatellite galaxy
A satellite galaxy orbits a larger galaxy due to gravitational attraction. Although a galaxy is made of a large number of objects which are not connected to each other, it has a center of mass, which represents a weighted average of the positions of each component object...
is common. A satellite's gravity could attract one of the primary's spiral arms. Or the satellite could dive in to the primary (e.g. Sagittarius Dwarf Elliptical Galaxy
Sagittarius Dwarf Elliptical Galaxy
The Sagittarius Dwarf Elliptical Galaxy is an elliptical loop-shaped satellite galaxy of the Milky Way Galaxy. It consists of four globular clusters, the main cluster being discovered in 1994...
). This could trigger a small amount of star formation
Star formation
Star formation is the process by which dense parts of molecular clouds collapse into a ball of plasma to form a star. As a branch of astronomy star formation includes the study of the interstellar medium and giant molecular clouds as precursors to the star formation process and the study of young...
.
Galaxy collision
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 mergingGalaxy merger
Galaxy mergers can occur when two galaxies collide. They are the most violent type of galaxy interaction. Although galaxy mergers do not involve stars or star systems actually colliding, due to the vast distances between stars in most circumstances, the gravitational interactions between galaxies...
. 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.
Galaxy collisions are now frequently simulated on computers, with all
the realistic physics, including gravity forces, gas dissipation, star formation and feedback. Dynamical friction slows down galaxy pairs, which may or may not merge at some point, according to the initial relative energy of the orbits. A simulated library of galaxy collisions can be found at the Paris Observatory website: GALMER
Galactic cannibalism
Galactic cannibalism refers to the process by which a large galaxyGalaxy
A galaxy is a massive, gravitationally bound system that consists of stars and stellar remnants, an interstellar medium of gas and dust, and an important but poorly understood component tentatively dubbed dark matter. The word galaxy is derived from the Greek galaxias , literally "milky", a...
, through tidal
Galactic tide
A galactic tide is a tidal force experienced by objects subject to the gravitational field of a galaxy such as the Milky Way. Particular areas of interest concerning galactic tides include galactic collisions, the disruption of dwarf or satellite galaxies, and the Milky Way's tidal effect on the...
gravitational interactions with a companion, merges with that companion, resulting in a larger, often irregular galaxy
Irregular galaxy
An irregular galaxy is a galaxy that does not have a distinct regular shape, like a spiral or an elliptical galaxy. The shape of an irregular galaxy is uncommon – they do not fall into any of the regular classes of the Hubble sequence, and they are often chaotic in appearance, with neither a...
.
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
Elliptical galaxy
An elliptical galaxy is a galaxy having an approximately ellipsoidal shape and a smooth, nearly featureless brightness profile. They range in shape from nearly spherical to highly flat and in size from hundreds of millions to over one trillion stars...
may also result.
It has been suggested that galactic cannibalism is currently occurring between the Milky Way
Milky Way
The Milky Way is the galaxy that contains the Solar System. This name derives from its appearance as a dim un-resolved "milky" glowing band arching across the night sky...
and the Large and Small Magellanic Clouds
Magellanic Clouds
The two Magellanic Clouds are irregular dwarf galaxies visible in the southern hemisphere, which are members of our Local Group and are orbiting our Milky Way galaxy...
. Streams of gravitationally-attracted hydrogen
Hydrogen
Hydrogen is the chemical element with atomic number 1. It is represented by the symbol H. With an average atomic weight of , hydrogen is the lightest and most abundant chemical element, constituting roughly 75% of the Universe's chemical elemental mass. Stars in the main sequence are mainly...
arcing from these dwarf galaxies to the Milky Way is taken as evidence for this theory.
Notable interacting galaxies
| Name | Type | Distance (million ly) |
Magnitude Apparent magnitude The apparent magnitude of a celestial body is a measure of its brightness as seen by an observer on Earth, adjusted to the value it would have in the absence of the atmosphere... |
Notes |
|---|---|---|---|---|
| Whirlpool Galaxy Whirlpool Galaxy The Whirlpool Galaxy is an interacting grand-design spiral galaxy that is estimated to be 23 ± 4 million light-years from the Milky Way Galaxy. in the constellation Canes Venatici... (M51) |
SAc (SB0-a) | 37 | +8.4 | Satellite interacting with its primary |
| NGC 2207 and IC 2163 NGC 2207 and IC 2163 NGC 2207 and IC 2163 are a pair of colliding spiral galaxies about 80 million light-years away in the constellation Canis Major. Both galaxies were discovered by John Herschel in 1835. So far three supernovae have been observed in NGC 2207... |
SAc/SAbc | 114 | +11 | galaxies going through the first phase in galactic collision |
| Mice Galaxies Mice Galaxies NGC 4676, or the Mice Galaxies, are two spiral galaxies in the constellation Coma Berenices. About 290 million light-years away, they are presently in the process of colliding and merging... (IC 819/20) |
S0/SB(s)ab | 300 | +13.5 | galaxies going through the second phase in galactic collision |
| NGC 1097 NGC 1097 NGC 1097 is a barred spiral galaxy about 45 million light-years away in the constellation Fornax. As of 2006, three supernovae have been observed in NGC 1097.... |
SB(s)bc (E6) | 45 | +9.5 | Satellite interacting with its primary |
| Antennae Galaxies Antennae Galaxies The Antennae Galaxies are a pair of interacting galaxies in the constellation Corvus. They are currently going through a phase of starburst. They were discovered by William Herschel in 1785... (NGC 4038/9) |
SAc/SBm | 45 | +10.3 | galaxies going through the third phase in galactic collision |
| NGC 520 NGC 520 NGC 520 is a pair of colliding spiral galaxies about 90 million light-years away in the constellation Pisces. It has a H II nucleus.-External links:*... |
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 galaxyAndromeda Galaxy
The Andromeda Galaxy is a spiral galaxy approximately 2.5 million light-years from Earth in the constellation Andromeda. It is also known as Messier 31, M31, or NGC 224, and is often referred to as the Great Andromeda Nebula in older texts. Andromeda is the nearest spiral galaxy to the...
in about 4.5 billion years. It is thought that the two spiral galaxies
Spiral galaxy
A spiral galaxy is a certain kind of galaxy originally described by Edwin Hubble in his 1936 work The Realm of the Nebulae and, as such, forms part of the Hubble sequence. Spiral galaxies consist of a flat, rotating disk containing stars, gas and dust, and a central concentration of stars known as...
will merge to become an elliptical galaxy
Elliptical galaxy
An elliptical galaxy is a galaxy having an approximately ellipsoidal shape and a smooth, nearly featureless brightness profile. They range in shape from nearly spherical to highly flat and in size from hundreds of millions to over one trillion stars...
.
See also
- Galactic tideGalactic tideA galactic tide is a tidal force experienced by objects subject to the gravitational field of a galaxy such as the Milky Way. Particular areas of interest concerning galactic tides include galactic collisions, the disruption of dwarf or satellite galaxies, and the Milky Way's tidal effect on the...
- Galaxy mergerGalaxy mergerGalaxy mergers can occur when two galaxies collide. They are the most violent type of galaxy interaction. Although galaxy mergers do not involve stars or star systems actually colliding, due to the vast distances between stars in most circumstances, the gravitational interactions between galaxies...
- NGC 7318NGC 7318NGC 7318 are a set of galaxies about 300 million light-years away in the Constellation Pegasus...
- Whirlpool GalaxyWhirlpool GalaxyThe Whirlpool Galaxy is an interacting grand-design spiral galaxy that is estimated to be 23 ± 4 million light-years from the Milky Way Galaxy. in the constellation Canes Venatici...