Barred spiral galaxy

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NGC 1300, viewed nearly face-on; Hubble Space Telescope image Hubble2005-01-barred-spiral-galaxy-NGC1300.jpg
NGC 1300, viewed nearly face-on; Hubble Space Telescope image

A barred spiral galaxy is a spiral galaxy with a central bar-shaped structure composed of stars. [1] Bars are found in about half of all spiral galaxies. [2] [3] Bars generally affect both the motions of stars and interstellar gas within spiral galaxies and can affect spiral arms as well. [2] The Milky Way Galaxy, where the Solar System is located, is classified as a barred spiral galaxy. [4]

Contents

Edwin Hubble classified spiral galaxies of this type as "SB" (spiral, barred) in his Hubble sequence and arranged them into sub-categories based on how open the arms of the spiral are. SBa types feature tightly bound arms, while SBc types are at the other extreme and have loosely bound arms. SBb-type galaxies lie in between the two. SB0 is a barred lenticular galaxy. A new type, SBm, was subsequently created to describe somewhat irregular barred spirals, such as the Magellanic Clouds, which were once classified as irregular galaxies, but have since been found to contain barred spiral structures. Among other types in Hubble's classifications for the galaxies are the spiral galaxy, elliptical galaxy and irregular galaxy.

Bars

Barred spiral galaxy IC 5201, located more than 40 million light-years from Earth. It was discovered by Joseph Lunt. A closer look at IC 5201.jpg
Barred spiral galaxy IC 5201, located more than 40 million light-years from Earth. It was discovered by Joseph Lunt.

Barred galaxies are apparently predominant, with surveys showing that up to two-thirds of all spiral galaxies contain a bar. [6] The current hypothesis is that the bar structure acts as a type of stellar nursery, fueling star birth at their centers. The bar is thought to act as a mechanism that channels gas inwards from the spiral arms through orbital resonance, in effect funneling the flow to create new stars. [7] This process is also thought to explain why many barred spiral galaxies have active galactic nuclei, such as that seen in the Southern Pinwheel Galaxy.

The creation of the bar is generally thought to be the result of a density wave radiating from the center of the galaxy whose effects reshape the orbits of the inner stars. This effect builds over time to stars orbiting further out, which creates a self-perpetuating bar structure. [8]

Bars are thought to be temporary phenomena in the lives of spiral galaxies; the bar structures decay over time, transforming galaxies from barred spirals to more "regular" spiral patterns. Past a certain size the accumulated mass of the bar compromises the stability of the overall bar structure. Barred spiral galaxies with high mass accumulated in their center tend to have short, stubby bars. [9] Since so many spiral galaxies have bar structures, it is likely that they are recurring phenomena in spiral galaxy development. The oscillating evolutionary cycle from spiral galaxy to barred spiral galaxy is thought to take on the average about two billion years. [10]

Recent studies have confirmed the idea that bars are a sign of galaxies reaching full maturity as the "formative years" end. A 2008 investigation found that only 20 percent of the spiral galaxies in the distant past possessed bars, compared with about 65 percent of their local counterparts. [11]

Milky Way Galaxy spiral arms - based on WISE data. PIA19341-MilkyWayGalaxy-SpiralArmsData-WISE-20150603.jpg
Milky Way Galaxy spiral arms - based on WISE data.

Grades

NGC 7640 is a barred spiral galaxy in the Andromeda constellation. NGC 7640 a spiral in Andromeda.jpg
NGC 7640 is a barred spiral galaxy in the Andromeda constellation.

The general classification is "SB" (spiral barred). The sub-categories are based on how open or tight the arms of the spiral are. SBa types feature tightly bound arms. SBc types are at the other extreme and have loosely bound arms. SBb galaxies lie in between. SBm describes somewhat irregular barred spirals. SB0 is a barred lenticular galaxy.

Examples

Example Type ImageInformation
NGC 2787 SB0 NGC 2787.jpg SB0 is a type of lenticular galaxy
NGC 4314 SBa NGC 4314HST1998-21-b-full.jpg
NGC 4921 SBab NGC 4921 by HST.jpg
Messier 95 SBb Messier95 spitzer.jpg
NGC 3953 SBbc NGC3953HunterWIlson.jpg
NGC 1073 SBc Barred spiral galaxy NGC 1073 (captured by the Hubble Space Telescope).tif
Messier 108 SBcd Messier108.jpg
NGC 2903 SBd NGC 2903 GALEX.jpg
NGC 5398 SBdm NGC 5398SST.jpg SBdm can also be considered a type

of barred Magellanic spiral

NGC 55 SBm Phot-14a-09-fullres.jpg SBm is a type of Magellanic spiral (Sm)

Other examples

NameImage Type Constellation
M58 M58s.jpg SBc Virgo
M91 Messier91.jpg SBb Coma Berenices
M95 Messier 95.jpg SBb Leo
M109 Messier object 109.jpg SBb Ursa Major
NGC 1300 Hubble2005-01-barred-spiral-galaxy-NGC1300.jpg SBbc Eridanus
NGC 7541 Bars and Baby Stars - potw2004a.jpg SB(rs)bcpec Pisces
NGC 1365 Phot-08a-99-hires.jpg SBc Fornax
NGC 2217 NGC 2217 ESO.jpg SBa Canis Major
Magellanic Clouds Magellanic Clouds -- Irregular Dwarf Galaxies.jpg SBm Dorado, Tucana
UGC 12158 UGC 12158.jpg SB Pegasus
NGC 1512 [13] NGC 1512.jpg SB(r)ab Horologium

See also

Related Research Articles

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Galaxy Gravitationally bound astronomical 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.

Large Magellanic Cloud Magellanic spiral galaxy that is a satellite of the Milky Way in the constellation Dorado

The Large Magellanic Cloud (LMC) is a satellite galaxy of the Milky Way. At a distance of around 50 kiloparsecs (≈160,000 light-years), the LMC is the second or third closest galaxy to the Milky Way, after the Sagittarius Dwarf Spheroidal (~16 kpc) and the possible dwarf irregular galaxy known as the Canis Major Overdensity. Based on readily visible stars and a mass of approximately 10 billion solar masses, the diameter of the LMC is about 14,000 light-years (4.3 kpc). It is roughly a hundredth as massive as the Milky Way and is the fourth largest galaxy in the Local Group, after the Andromeda Galaxy (M31), the Milky Way, and the Triangulum Galaxy (M33).

Hubble sequence Galaxy morphological classification scheme invented by Edwin Hubble

The Hubble sequence is a morphological classification scheme for galaxies invented by Edwin Hubble in 1926. It is often colloquially known as the Hubble tuning fork diagram because the shape in which it is traditionally represented resembles a tuning fork.

Elliptical galaxy Galaxy having an approximately ellipsoidal shape and a smooth, nearly featureless brightness profile

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 classes of galaxy described by Edwin Hubble in his Hubble sequence and 1936 work The Realm of the Nebulae, along with spiral and lenticular galaxies. Elliptical (E) galaxies are, together with lenticular galaxies (S0) with their large-scale disks, and ES galaxies with their intermediate scale disks, a subset of the "early-type" galaxy population.

Spiral galaxy Galaxy having a number of arms of younger stars

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.

Irregular galaxy Galaxy not having a distinct regular shape

An irregular galaxy is a galaxy that does not have a distinct regular shape, unlike a spiral or an elliptical galaxy. Irregular galaxies do not fall into any of the regular classes of the Hubble sequence, and they are often chaotic in appearance, with neither a nuclear bulge nor any trace of spiral arm structure.

Lenticular galaxy Type of galaxy intermediate between an elliptical and a spiral galaxy

A lenticular galaxy is a type of galaxy intermediate between an elliptical and a spiral galaxy in galaxy morphological classification schemes. It contains a large-scale disc but does not have large-scale spiral arms. Lenticular galaxies are disc galaxies that have used up or lost most of their interstellar matter and therefore have very little ongoing star formation. They may, however, retain significant dust in their disks. As a result, they consist mainly of aging stars. Despite the morphological differences, lenticular and elliptical galaxies share common properties like spectral features and scaling relations. Both can be considered early-type galaxies that are passively evolving, at least in the local part of the Universe. Connecting the E galaxies with the S0 galaxies are the ES galaxies with intermediate-scale discs.

Galactic bulge Tightly packed group of stars within a larger formation

In astronomy, a galactic bulge is a tightly packed group of stars within a larger star formation. The term almost exclusively refers to the central group of stars found in most spiral galaxies. Bulges were historically thought to be elliptical galaxies that happened to have a disk of stars around them, but high-resolution images using the Hubble Space Telescope have revealed that many bulges lie at the heart of a spiral galaxy. It is now thought that there are at least two types of bulges: bulges that are like ellipticals and bulges that are like spiral galaxies.

Galaxy morphological classification System for categorizing galaxies based on appearance

Galaxy morphological classification is a system used by astronomers to divide galaxies into groups based on their visual appearance. There are several schemes in use by which galaxies can be classified according to their morphologies, the most famous being the Hubble sequence, devised by Edwin Hubble and later expanded by Gérard de Vaucouleurs and Allan Sandage. However, galaxy classification and morphology are now largely done using computational methods and physical morphology.

Dwarf galaxy Small galaxy composed of up to several billion stars

A dwarf galaxy is a small galaxy composed of about 1000 up to several billion stars, as compared to the Milky Way's 200–400 billion stars. The Large Magellanic Cloud, which closely orbits the Milky Way and contains over 30 billion stars, is sometimes classified as a dwarf galaxy; others consider it a full-fledged galaxy. Dwarf galaxies' formation and activity are thought to be heavily influenced by interactions with larger galaxies. Astronomers identify numerous types of dwarf galaxies, based on their shape and composition.

Milky Way Barred spiral galaxy containing our Solar System

The Milky Way is the galaxy that includes our Solar System, with the name describing the galaxy's appearance from Earth: a hazy band of light seen in the night sky formed from stars that cannot be individually distinguished by the naked eye. The term Milky Way is a translation of the Latin via lactea, from the Greek γαλακτικός κύκλος, meaning "milky circle." From Earth, the Milky Way appears as a band because its disk-shaped structure is viewed from within. Galileo Galilei first resolved the band of light into individual stars with his telescope in 1610. Until the early 1920s, most astronomers thought that the Milky Way contained all the stars in the Universe. Following the 1920 Great Debate between the astronomers Harlow Shapley and Heber Curtis, observations by Edwin Hubble showed that the Milky Way is just one of many galaxies.

Interacting galaxy Galaxies whose gravitational fields result in the disturbance of one another.

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 Barred spiral galaxy in the constellation Horologium

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 2903 Isolated barred spiral galaxy in the constellation Leo

NGC 2903 is an isolated barred spiral galaxy in the equatorial constellation of Leo, positioned about 1.5° due south of Lambda Leonis. It was discovered by German-born astronomer William Herschel, who cataloged it on November 16, 1784. He mistook it as a double nebula, as did subsequent observers, and it wasn't until the nineteenth century that the Third Earl of Rosse resolved into a spiral form. J. L. E. Dreyer assigned it the identifiers 2903 and 2905 in his New General Catalogue; NGC 2905 now designates a luminous knot in the northeastern spiral arm.

NGC 4314 Barred spiral galaxy in the constellation Coma Berenices

NGC 4314 is a barred spiral galaxy approximately 53 million light-years away in the northern constellation of Coma Berenices. It is positioned around 3° to the north and slightly west of the star Gamma Comae Berenices and is visible in a small telescope. The galaxy was discovered by German-born astronomer William Herschel on March 13, 1785. It was labelled as peculiar by Allan Sandage in 1961 because of the unusual structure in the center of the bar. NGC 4314 is a member of the Coma I group of galaxies.

NGC 6782 Barred spiral galaxy in the constellation Pavo

NGC 6782 is a barred spiral galaxy located in the southern constellation of Pavo, at a distance of approximately 173 megalight-years from the Milky Way. It was discovered on July 12, 1834 by English astronomer John Herschel. John L. E. Dreyer described it as, "considerably faint, considerably small, round, a little brighter middle, 9th magnitude star to south". The morphological classification of NGC 6782 is (R1R′2)SB(r)a, indicating a barred spiral galaxy with a multiple ring system and tightly-wound spiral arms. It is seen nearly face-on, being inclined by an angle of 27.2°±0.2° to the line of sight from the Earth.

NGC 7424 Barred spiral galaxy in the constellation Grus

NGC 7424 is a barred spiral galaxy located 37.5 million light-years away in the southern constellation Grus. Its size makes it similar to our own galaxy, the Milky Way. It is called a "grand design" galaxy because of its well defined spiral arms. One supernova and two ultraluminous X-ray sources have been discovered in NGC 7424.

UGC 2885 Spiral galaxy in the constellation Perseus

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 3081 Barred lenticular ring galaxy in the constellation Hydra

NGC 3081 is a barred lenticular ring galaxy in the constellation of Hydra. NGC 3081 is located about 85 million light-years away from Earth, which means, given its apparent dimensions, that NGC 3081 is approximately 60,000 light years across. It is a type II Seyfert galaxy, characterised by its bright nucleus. It was discovered by William Herschel on 21 December 1786.

References

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