 | This articleneeds additional citations forverification. Please helpimprove this article byadding citations to reliable sources. Unsourced material may be challenged and removed. Find sources: "Interacting galaxy" – news ·newspapers ·books ·scholar ·JSTOR(May 2009) (Learn how and when to remove this message) |
Interacting galaxies (colliding galaxies) aregalaxies whosegravitational 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.[1] An example of a minor interaction is asatellite galaxy disturbing the primary galaxy'sspiral arms. An example of a major interaction is a galactic collision, which may lead to agalaxy merger.
A giant galaxy interacting with itssatellites is common. A satellite's gravity could attract one of the primary'sspiral arms. Alternatively, the secondary satellite can dive into the primary galaxy, as in theSagittarius Dwarf Elliptical Galaxy diving into theMilky Way. That can possibly trigger a small amount ofstar formation. Such orphaned clusters of stars were sometimes referred to as "blue blobs" before they were recognized as stars.[1]
Colliding galaxies are common duringgalaxy evolution.[3] 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.[2]
Colliding may lead tomerging if two galaxies collide and do not have enough momentum to continue traveling after the collision. As with othergalaxy collisions, the merging of two galaxies may create astarburst region of new stars.[4] 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.[5] 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.[6]
Galaxy harassment is a type of interaction between a low-luminosity galaxy and a brighter one that takes place within richgalaxy clusters, such asVirgo andComa, where galaxies are moving at highrelative speeds and suffering frequent encounters with other systems of the cluster due to the high galactic density.
According tocomputer simulations, the interactions convert the affected galaxy disks into disturbedbarred spiral galaxies and producesstarbursts followed by, if more encounters occur, loss ofangular momentum and heating of their gas. The result would be the conversion of (late type) low-luminosity spiral galaxies intodwarf spheroidals anddwarf ellipticals.[7]
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 formerdisc systems transformed by the above-mentioned interactions.[8] The existence of similar structures in isolated early-type dwarf galaxies, such asLEDA 2108986, has undermined this hypothesis.[9][10]
| Name | Type | Distance (millionly) | Magnitude | Notes |
|---|---|---|---|---|
| Milky Way Galaxy,LMC andSMC | 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 |
| Butterfly Galaxies NGC 4567/8 | SA(rs)bc / SA(rs)bc | 60 | +10.9 | Early phase of interaction |
| NGC 2207 and IC 2163 | SAc/SAbc | 114 | +11 | Galaxies going through thefirst phase in galactic collision |
| Mice Galaxies (NGC 4676A and NGC 4676B) | S0/SB(s)ab | 300 | +13.5 | Galaxies going through thesecond phase in galactic collision |
| Antennae Galaxies (NGC 4038/9) | SAc/SBm | 45 | +10.3 | Galaxies going through thethird phase in galactic collision |
| NGC 520 | S | 100 | +11.3 | Galaxies going through thethird phase in galactic collision |
| NGC 2936 | Irr | 352 | +12.9 | ? |
Astronomers have estimated theMilky Way Galaxy will collide with theAndromeda Galaxy 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.[11] Some think the twospiral galaxies will eventually merge to become anelliptical galaxy whose gravitational interactions will fling various celestial bodies outward, evicting them from the resulting elliptical galaxy.[12][13] or perhaps a largedisc galaxy.[14]
