Interacting galaxy

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 disturbing the primary galaxy's spiral arms. An example of a major interaction is a galactic collision, which may lead to a galaxy merger.

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

Satellite interaction

A giant galaxy interacting with its satellites is common. A satellite's gravity could attract one of the primary's spiral arms. Alternatively, the secondary satellite can dive into the primary galaxy, as in the Sagittarius Dwarf Elliptical Galaxy diving into the Milky Way. That can possibly trigger a small amount of star formation. Such orphaned clusters of stars were sometimes referred to as "blue blobs" before they were recognized as stars.^[1]

Animation of Galaxy Collision

Galaxy collision

Gravitationally lensed galactic merger H-ATLAS J142935.3-002836.^[2]

Colliding galaxies are common during galaxy 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.

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.^[4] 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 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.^[5]

Gallery

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  UGC 2369 taken by HST.^[6]
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  Close encounter at IRAS 06076-2139.^[7]
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  Interacting galaxies NGC 4302 and NGC 4298 both located 55 million light-years away.^[8]
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  Galaxy NGC 6052 merging into a single structure.^[9]
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  Galaxy pair Zw I 136.^[10]
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  ESO 576-69 is believed to be the nucleus of a former spiral galaxy.^[11]
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  The Whirlpool Galaxy with its satellite NGC 5195.
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  The Mice Galaxies.
• This simulation follows the collision of two spiral galaxies that harbour giant black holes.
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  NGC 3447 comprises a couple of interacting galaxies.^[12]
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  Barred spiral galaxy NGC 1512 in the process of a lengthy merger with NGC 1510, a dwarf elliptical galaxy.
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  ESO 593-8 is an impressive pair of interacting galaxies with a feather-like galaxy crossing a companion galaxy.
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  Antennae Galaxies NGC 4038 & NGC 4039 are a pair of interacting galaxies in the constellation Corvus.
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  2MASX J09133888-1019196, an interacting galaxy in the constellation of Hydra located 700 million light-years away. Both galaxies are beginning to merge, with a separation gap of only 130,000 light-years.^[13]
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  Interacting galaxy pair, ESO 77-14 located in the constellation Indus. These galaxies are currently in a gravitational tug of war with each other, distorting their appendences.^[14]

Galactic cannibalism

2MASX J16270254+4328340 galaxy has merged with another galaxy leaving a fine mist, made of millions of stars, spewing from it in long trails.^[15]

Galactic cannibalism is a common phenomenon.^[16] It refers to the process in which a large galaxy, through tidal gravitational interactions with a companion, merges with that companion. The most common result of the gravitational merger between two or more galaxies is a larger irregular galaxy, but 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 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 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.

According to computer simulations, 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 and heating of their gas. The result would be the conversion of (late type) low-luminosity spiral galaxies into dwarf spheroidals and dwarf ellipticals.^[17]

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.^[18] The existence of similar structures in isolated early-type dwarf galaxies, such as LEDA 2108986, has undermined this hypothesis.^[19][20]

Notable examples

Montage of some well known 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
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 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
NGC 2936	Irr	352	+12.9	?

Andromeda–Milky Way collision

Main article: Andromeda–Milky Way collision

Astronomers have estimated the Milky Way Galaxy will collide with the Andromeda Galaxy in about 4.5 billion years. Some think the two spiral galaxies will eventually merge to become an elliptical galaxy whose gravitational interactions will fling various celestial bodies outward, evicting them from the resulting elliptical galaxy.^[21][22] or perhaps a large disc galaxy.^[23]

See also

• NGC 7318

References

1. "HubbleSite: News - Hubble Finds that "Blue Blobs" in Space Are Orphaned Clusters of Stars". hubblesite.org. Retrieved 2017-05-24.
2. "Best View Yet of Merging Galaxies in Distant Universe". ESO Press Release. Retrieved 26 August 2014.
3. Nola Taylor Tillman (April 21, 2015). "How the Hubble Space Telescope Changed Our View of the Cosmos". Space.com.
4. Gianopoulos, Andrea (2022-02-18). "Galaxy Collision Creates 'Space Triangle' in New Hubble Image". NASA. Retrieved 2022-12-01.
5. "GALMER". Retrieved 27 March 2010.
6. "Galactic Creatures at Play". www.spacetelescope.org. Retrieved 10 August 2019.
7. "Close encounter". www.spacetelescope.org. Retrieved 8 May 2017.
8. "A close galactic pair". www.spacetelescope.org. Archived from the original on 20 April 2017. Retrieved 21 April 2017.
9. "Two become one". Archived from the original on 31 December 2015. Retrieved 28 December 2015.
10. "Galactic soup". ESA/Hubble Picture of the Week. Archived from the original on 10 June 2020. Retrieved 18 August 2014.
11. "The messy result of a galactic collision". ESA/Hubble Picture of the Week. Archived from the original on 24 November 2020. Retrieved 29 May 2013.
12. "Defying cosmic convention". www.spacetelescope.org. Retrieved 20 March 2017.
13. "Hubble Interacting Galaxy 2MASX J09133888-1019196". HubbleSite. Retrieved 2024-08-30.
14. "Hubble Interacting Galaxy ESO 77-14". HubbleSite. Retrieved 2024-08-30.
15. "The last waltz". Retrieved 14 December 2015.
16. "APOD: 2010 July 17 - Galaxies in the River". apod.nasa.gov. Retrieved 2022-12-01.
17. "Galaxy Harassment". supernova.lbl.gov.
18. Barazza, F. D.; Binggeli, B.; Jerjen, H. (September 2002). "More evidence for hidden spiral and bar features in bright early-type dwarf galaxies". Astronomy & Astrophysics. 391 (3): 823–831. arXiv:astro-ph/0206275. Bibcode:2002A&A...391..823B. doi:10.1051/0004-6361:20020875. ISSN 0004-6361. S2CID 844270.
19. Graham, Alister W.; Janz, Joachim; Penny, Samantha J.; Chilingarian, Igor V.; Ciambur, Bogdan C.; Forbes, Duncan A.; Davies, Roger L. (May 2017). "Implications for the Origin of Early-type Dwarf Galaxies: A Detailed Look at the Isolated Rotating Early-type Dwarf Galaxy LEDA 2108986 (CG 611), Ramifications for the Fundamental Plane's {S}_{K}^{2} Kinematic Scaling, and the Spin-Ellipticity Diagram". The Astrophysical Journal. 840 (2): 68. arXiv:1705.03587. Bibcode:2017ApJ...840...68G. doi:10.3847/1538-4357/aa6e56. ISSN 0004-637X.
20. Janz, Joachim; Penny, Samantha J.; Graham, Alister W.; Forbes, Duncan A.; Davies, Roger L. (July 2017). "Implications for the origin of early-type dwarf galaxies – the discovery of rotation in isolated, low-mass early-type galaxies". Monthly Notices of the Royal Astronomical Society. 468 (3): 2850–2864. arXiv:1703.04975. Bibcode:2017MNRAS.468.2850J. doi:10.1093/mnras/stx634. ISSN 0035-8711.
21. Hazel, Muir (14 May 2007). "Galactic merger to 'evict' Sun and Earth". New Scientist. Archived from the original on 20 April 2014. Retrieved 2014-10-07.
22. Loeb, Abraham; Cox, T. J. (June 2008). "Our galaxy's collision with Andromeda". Astronomy. p. 28.
23. Junko Ueda; et al. (2014). "Cold molecular gas in merger remnants. I. Formation of molecular gas disks". The Astrophysical Journal Supplement Series. 214 (1): 1. arXiv:1407.6873. Bibcode:2014ApJS..214....1U. doi:10.1088/0067-0049/214/1/1. S2CID 716993.

External links

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