This is a list of ring galaxies. A ring galaxy, as the name suggests, is a disc or spiral galaxy with its galactic disc structured or distorted into a ring or torus-like appearance. Hoag's Object, discovered by Art Hoag in 1950, is the prototypical example of a ring galaxy.
Ring galaxies are theorized to be formed through multiple possible situations-
1. Bar instability – a phenomenon where the rotational velocity of the bar in a barred spiral galaxy increases to the point of spiral spin-out. Under typical conditions, gravitational density waves would favor the creation of spiral arms. When bar instability occurs, these density waves are instead migrated out into a ring-structure by the pressure, force, and gravitational influence of the byronic and dark matter furiously orbiting about the bar. This migration forces the stars, gas and dust found within the former arms into a torus-like region, forming a ring, and often igniting star formation.
2. Galactic collisions- another observed way that ring galaxies can form is through the process of two or more galaxies colliding. The cartwheel galaxy, galaxy pair AM 2026-424, and Arp 147 are all examples of ring galaxies believed to be formed from this process. In pass-through galactic collisions, an often smaller galaxy will pass through the disc of an often larger spiral, causing an outward push of the arms, as if dropping a rock into a pond of still water. In side-swipe and head-on collisions, the appearance of a perfect ring are less likely, with chaotic and warped appearances dominating.
3. Intergalactic medium accretion- this method has been inferred through the existence of Hoags object, along with UV observations of several other large and ultra-large super spiral galaxies and current formation theories of spiral galaxies. UV-light observations show several cases of faint, ring-like and spiral structures of hot young stars that have formed along the network of cooled inflowing gas, extending far from the visible luminous galactic disc. If conditions are favorable, a ring can form in the place of a spiral structure. Since some spiral galaxies are theorized to have formed from massive clouds of intergalactic gas collapsing and then rotationally forming into a disc structure, one could assume that a ring disc could form in place of a spiral disc if, as mentioned before, conditions are favorable. This holds true for protogalaxies, or galaxies just throughout to be forming, and old galaxies that has migrated into a section of space with a higher gas content than its previous locations.
|Cartwheel Galaxy||ESO 350-40, PGC 2248||500 Mly||lenticular galaxy|
|NGC 6028||NGC 6028, NGC 6046, PGC 56716||203 Mly||barred lenticular galaxy|
|Hoag's Object||PGC 54559, PRC D-51||600 Mly|
|SDSS J151713.93+213516.8||This galaxy can be seen behind Hoag's Object|
|AM 0644-741||AM 0644-741||300 Mly|
|NGC 1291||NGC 1291, NGC 1269, PGC 012209||33 Mly|
|NGC 1512||PGC 14391||38 Mly||Galaxy exhibits a double-ring structure|
|NGC 1433||PGC 13586||49 Mly||barred spiral galaxy with ring|
|NGC 1533||NGC 1533, PGC 14582||62 ± 4 Mly||lenticular galaxy with ring structure|
|NGC 2859||UGC 5001, PGC 26649||82.8 Mly||lenticular galaxy with ring structure|
|NGC 1350||PGC 013059||87.4 Mly||spiral galaxy with ring structure|
|NGC 1386||PGC 13333||53 Mly||spiral galaxy with ring structure|
|NGC 1387||PGC 13344||53 Mly||lenticular galaxy with nuclear ring|
|NGC 4622||PGC 42701||200 Mly||unbarred spiral galaxy with ring|
|NGC 4777||NGC 4777, PGC 43852||180 Mly|
|NGC 7217||UGC 11914, PGC 68096||50 Mly||unbarred spiral galaxy with ring|
|II Zw 28||Zw II 28, 2MASX J05014205+0334278|
|Mayall's Object||Arp 148, VV 032, MCG+07-23-019, APG 148||450 Mly||collisional ring galaxy|
|I Zw 045||I Zw 045, NGC 4774||collisional ring galaxy|
|VII Zw 466||VII Zw 466, UGC 07683||collisional ring galaxy|
|Arp 10||Arp 10, UGC 01775, 2MASX J02182639+0539139||collisional ring galaxy|
|Arp 147||IC 298||interacting pair|
|NGC 4650A||PGC 42951||polar ring galaxy|
|NGC 660||polar ring galaxy|
|NGC 922||ESO 478-28, ISG 10||150 Mly||collisional ring galaxy|
|ESO 198-13||PGC 9463||240 Mly||three ring structures|
|LEDA 1000714||PGC 1000714, 6dFGS gJ112316.4-084007, 2MASX J11231643-0840067||360 Mly||two nearly round rings, but with different characteristics|
|NGC 985||VV 285, Mrk 1048, MCG -02-07-035, PGC 9817||567 Mly||collisional ring galaxy|
|NGC 1142||NGC 1144, UGC 2389, Arp 118, VV 331a, Mrk 1504, CGCG 389-046, MCG +00-08-048, PGC 11012||375 Mly||Seyfert galaxy|
|NGC 3081||IC 2529, ESO 499-G31, AM 0957-223, MCG -04-24-012, PGC 28876||83 Mly||barred lenticular galaxy|
|NGC 3821||CGCG 127-32, MCG 4-28-30, PGC 36314, UGC 6663||271 Mly||low surface brightness galaxy|
|NGC 4513||CGCG 315-42, MCG 11-15-59, PGC 41527, UGC 7683||110 Mly||lenticular galaxy|
|NGC 7020||NGC 7021, ESO 107-13, PGC 66291||138 Mly||barred lenticular galaxy|
|NGC 7098||ESO 48-5, IRAS 21393-7520, PGC 67266||95 Mly||double barred spiral galaxy|
|NGC 7552||IC 5294, ESO 291- G 012, VV 440, PGC 70884||56 Mly||barred spiral galaxy|
|NGC 7742||UGC 12760, MCG +02-60-010, UZC J234415.8+104601, 2MASX J23441571+1046015||72 Mly||Unbarred spiral galaxy with ring, Seyfert galaxy|
The study of galaxy formation and evolution is concerned with the processes that formed a heterogeneous universe from a homogeneous beginning, the formation of the first galaxies, the way galaxies change over time, and the processes that have generated the variety of structures observed in nearby galaxies. Galaxy formation is hypothesized to occur from structure formation theories, as a result of tiny quantum fluctuations in the aftermath of the Big Bang. The simplest model in general agreement with observed phenomena is the Lambda-CDM model—that is, that clustering and merging allows galaxies to accumulate mass, determining both their shape and structure.
A galaxy is a gravitationally bound system of stars, stellar remnants, interstellar gas, dust, and dark matter. The word galaxy is derived from the Greek galaxias (γαλαξίας), literally "milky", a reference to the Milky Way. Galaxies range in size from dwarfs with just a few hundred million stars to giants with one hundred trillion stars, each orbiting its galaxy's center of mass.
Hoag's Object is a non-typical galaxy of the type known as a ring galaxy. The galaxy is named after Arthur Hoag who discovered it in 1950 and identified it as either a planetary nebula or a peculiar galaxy with eight billion stars, spanning roughly 100,000 light years.
Spiral galaxies form a class of galaxy originally described by Edwin Hubble in his 1936 work The Realm of the Nebulae and, as such, form part of the Hubble sequence. Most spiral galaxies consist of a flat, rotating disk containing stars, gas and dust, and a central concentration of stars known as the bulge. These are often surrounded by a much fainter halo of stars, many of which reside in globular clusters.
A ring galaxy is a galaxy with a circle-like appearance. Hoag's Object, discovered by Art Hoag in 1950, is an example of a ring galaxy. The ring contains many massive, relatively young blue stars, which are extremely bright. The central region contains relatively little luminous matter. Some astronomers believe that ring galaxies are formed when a smaller galaxy passes through the center of a larger galaxy. Because most of a galaxy consists of empty space, this "collision" rarely results in any actual collisions between stars. However, the gravitational disruptions caused by such an event could cause a wave of star formation to move through the larger galaxy. Other astronomers think that rings are formed around some galaxies when external accretion takes place. Star formation would then take place in the accreted material because of the shocks and compressions of the accreted material.
Messier 94 is a spiral galaxy in the mid-northern constellation Canes Venatici. It was discovered by Pierre Méchain in 1781, and catalogued by Charles Messier two days later. Although some references describe M94 as a barred spiral galaxy, the "bar" structure appears to be more oval-shaped. The galaxy has two ring structures.
NGC 1365, also known as the Great Barred Spiral Galaxy, is a double-barred spiral galaxy about 56 million light-years away in the constellation Fornax.
The Cartwheel Galaxy (also known as ESO 350-40 or PGC 2248) is a lenticular galaxy and ring galaxy about 500 million light-years away in the constellation Sculptor. It is an estimated 150,000 light-years diameter, and has a mass of about 2.9–4.8 × 109 solar masses; its outer ring has a circular velocity of 217 km/s.
Interacting 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 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 one ring around the galactic nucleus and another further out in the main disk. The galaxy hosts an extended UV disc with at least 200 clusters with recent star formation activity. NGC 1512 is a member of the Dorado Group.
NGC 4625 is a distorted dwarf galaxy in the constellation Canes Venatici. The galaxy is formally classified as a Sm galaxy, which means that its structure vaguely resembles the structure of spiral galaxies. The galaxy is sometimes referred to as a Magellanic spiral because of its resemblance to the Magellanic clouds.
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 Oort cloud of the Solar System.
NGC 1533 is a barred lenticular galaxy with faint spiral structure in the constellation Dorado. The seventh-brightest member of the Dorado Group and 1° off the group's center, it is surrounded by a vast arc or ring of H I which is connected to IC 2038 and IC 2039. The ring orbits around 32 kpc from the center. As is typical of lenticular galaxies, star formation is weak in NGC 1533. Using both the surface brightness fluctuation (SBF) and globular cluster luminosity function (GCLF) methods, its distance was estimated in 2007 to be 19.4 ± 1.1 Mpc and 18.6 ± 2.0 Mpc respectively. Averaging these together gives a distance of around 19 million parsecs or 62 million light-years from earth. In 1970, a supernova was detected in NGC 1533.
Galactic clusters are gravitationally bound large-scale structures of multiple galaxies. The evolution of these aggregates is determined by time and manner of formation and the process of how their structures and constituents have been changing with time. Gamow (1952) and Weizscker (1951) showed that the observed rotations of galaxies are important for cosmology. They postulated that the rotation of galaxies might be a clue of physical conditions under which these systems formed. Thus, understanding the distribution of spatial orientations of the spin vectors of galaxies is critical to understanding the origin of the angular momenta of galaxies.
UGC 2885 is a large barred spiral galaxy of type SA(rs)c in the constellation Perseus. It is 232 million light-years (71 Mpc) from Earth and measures 463,000 ly (142,000 pc) across, making it one of the largest known spiral galaxies. It is also a possible member of the Pisces-Perseus supercluster.
NGC 4138 is the New General Catalogue identifier for a lenticular galaxy in the northern constellation of Canes Venatici. Located around 52 million light years from Earth, it spans some 2.1 × 1.3 arc minutes and has an apparent visual magnitude of 11.3. The morphological classification of NGC 4138 is SA0+(r), indicating it lacks a bar formation and has tightly wound spiral arms with a ring-like structure around the nucleus. It has no nearby companion galaxies.
The following outline is provided as an overview of and topical guide to galaxies:
NGC 7013 is a relatively nearby spiral or lenticular galaxy estimated to be around 37 to 41.4 million light-years away from Earth in the constellation of Cygnus. NGC 7013 was discovered by English astronomer William Herschel on July 17, 1784 and was also observed by his son, astronomer John Herschel on September 15, 1828.
NGC 7469 is an intermediate spiral galaxy in the constellation of Pegasus. NGC 7469 is located about 200 million light years away from Earth, which means, given its apparent dimensions, that NGC 7469 is approximately 90,000 light years across. It was discovered by William Herschel on November 12, 1784.
NGC 6951 is a barred spiral galaxy located in the constellation Cepheus. It is located at a distance of about 75 million light-years from Earth, which, given its apparent dimensions, means that NGC 6951 is about 100,000 light-years across. It was discovered by Jérôme Eugène Coggia in 1877 and independently by Lewis Swift in 1878.