Flocculent spiral galaxy

A flocculent spiral galaxy is a type of spiral galaxy. Unlike the well-defined spiral architecture of a grand design spiral galaxy, flocculent (meaning "fluffy") galaxies are patchy, with discontinuous spiral arms.[1][2] Self-propagating star formation is the apparent explanation for the structure of flocculent spirals.[3] Approximately 30% of spirals are flocculent, 10% are grand design, and the rest are referred to as "multi-armed".[4] The multiple-arm type is sometimes grouped into the flocculent category.[5]

The prototypical flocculent spiral is NGC 2841.[6]

NGC 2841 Hubble WikiSky
NGC 2841, the prototypical flocculent spiral galaxy

Examples

Example Class Image Constellation Notes
NGC 4414 SA(rs)c NGC 4414 (NASA-med) Coma Berenices [7]
NGC 2841 SA(r)b NGC 2841 Hubble WikiSky Ursa Major [6]
NGC 3521 SAB(rs)bc NGC3521-eso1129a Leo [6]
NGC 7793 SA(s)d Phot-14b-09-fullres 2 Sculptor [6]
Sunflower Galaxy
(Messier 63)
SAB(rs)cd M63 (NGC 5055) Canes Venatici [8]

References

  1. ^ COSMOS - SAO Encyclopedia of Astronomy, "Grand Design Spiral" (accessed 23 April 2010)
  2. ^ COSMOS - SAO Encyclopedia of Astronomy, "Flocculent Spiral" (accessed 23 April 2010)
  3. ^ Masters, Karen (September 2002), What is the Origin of Spiral Structure in Galaxies, archived from the original on 2007-06-09, retrieved 2007-05-30
  4. ^ Case Western Reserve University, Chris Mihos, ASTR222 - Spring 2008, "Spiral Structure" (accessed 23 April 2010)
  5. ^ University of Virginia, Mark Whittle, ASTR 553/554 : Extragalactic Astronomy (2007), "Lecture 5: Spiral Galaxies" (accessed 23 April 2010)
  6. ^ a b c d "A Near-Infrared Atlas of Spiral Galaxies", Debra Meloy Elmegreen, "CH3. Discussion" (accessed 23 April 2010)
  7. ^ Nemiroff, R.; Bonnell, J., eds. (3 April 2002). "NGC 4414: A Flocculent Spiral Galaxy". Astronomy Picture of the Day. NASA. Retrieved 23 April 2010.
  8. ^ NASA (2015). [1]. Retrieved Mar. 2, 2017

Sources

External links

Coma Berenices

Coma Berenices is an ancient asterism in the northern sky which has been defined as one of the 88 modern constellations. It is located in the fourth galactic quadrant, between Leo and Boötes, and is visible in both hemispheres. Its name means "Berenice's Hair" in Latin and refers to Queen Berenice II of Egypt, who sacrificed her long hair as a votive offering. It was introduced to Western astronomy during the third century BC by Conon of Samos and was further corroborated as a constellation by Gerardus Mercator and Tycho Brahe. Coma Berenices is the only modern constellation named for a historic person.

The constellation's major stars are Alpha Comae Berenices, Beta Comae Berenices and Gamma Comae Berenices. They form a 45-degree triangle, from which Berenice's imaginary tresses, formed by the Coma Star Cluster, hang. The constellation's brightest star is Beta Comae Berenices, a 4.2-magnitude main sequence star similar to the Sun. Coma Berenices contains the North Galactic Pole and one of the richest known galaxy clusters, the Coma Cluster, part of the Coma Supercluster. Galaxy Malin 1, in the constellation, is the first-known giant low-surface-brightness galaxy. Supernova SN 2005ap discovered in Coma Berenices is the second-brightest known, and SN 1940B was the first observed example of a type II supernova. The star FK Comae Berenices is the prototype of an eponymous class of variable stars. The constellation is the radiant of one meteor shower, Coma Berenicids, which has one of the fastest meteor speeds, up to 65 kilometres per second (40 mi/s).

Coma I

The Coma I Group is a group of galaxies located about 14.5 Mpc (47.3 Mly) away in the constellation Coma Berenices. The brightest member of the group is NGC 4725. The Coma I Group is rich in spiral galaxies while containing few elliptical and lenticular galaxies. Coma I lies in the foreground of the more distant Coma and Leo clusters and is located within the Virgo Supercluster.The Coma I Group is currently infalling into the Virgo Cluster and will eventually merge with it.

Galaxy

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 (108) stars to giants with one hundred trillion (1014) stars, each orbiting its galaxy's center of mass.

Galaxies are categorized according to their visual morphology as elliptical, spiral, or irregular. Many galaxies are thought to have supermassive black holes at their centers. The Milky Way's central black hole, known as Sagittarius A*, has a mass four million times greater than the Sun. As of March 2016, GN-z11 is the oldest and most distant observed galaxy with a comoving distance of 32 billion light-years from Earth, and observed as it existed just 400 million years after the Big Bang.

Research released in 2016 revised the number of galaxies in the observable universe from a previous estimate of 200 billion (2×1011) to a suggested 2 trillion (2×1012) or more, containing more stars than all the grains of sand on planet Earth. Most of the galaxies are 1,000 to 100,000 parsecs in diameter (approximately 3000 to 300,000 light years) and separated by distances on the order of millions of parsecs (or megaparsecs). For comparison, the Milky Way has a diameter of at least 30,000 parsecs (100,000 LY) and is separated from the Andromeda Galaxy, its nearest large neighbor, by 780,000 parsecs (2.5 million LY).

The space between galaxies is filled with a tenuous gas (the intergalactic medium) having an average density of less than one atom per cubic meter. The majority of galaxies are gravitationally organized into groups, clusters, and superclusters. The Milky Way is part of the Local Group, which is dominated by it and the Andromeda Galaxy and is part of the Virgo Supercluster. At the largest scale, these associations are generally arranged into sheets and filaments surrounded by immense voids. The largest structure of galaxies yet recognised is a cluster of superclusters that has been named Laniakea, which contains the Virgo supercluster.

NGC 2841

NGC 2841 is an inclined unbarred spiral galaxy exhibiting a prominent inner ring structure in the constellation Ursa Major, it was discovered on 9 March 1788 by William Herschel. Initially thought to be about 30 million light years distant, a 2001 Hubble Space Telescope survey of the galaxy's Cepheid variables determined that it was approximately 14.1 megaparsecs or 46 million light years distant.

NGC 4212

NGC 4212 is a flocculent spiral galaxy with LINER activity located about 53 million light-years away in the constellation Coma Berenices. The galaxy was discovered by astronomer William Herschel on April 8, 1784 and was listed in the NGC catalog as NGC 4208. He then observed the same galaxy and listed it as NGC 4212. Astronomer John Louis Emil Dreyer later concluded that NGC 4208 was identical to NGC 4212. NGC 4212 is a member of the Virgo Cluster.

NGC 4237

NGC 4237 is a flocculent spiral galaxy located about 60 million light-years away in the constellation Coma Berenices. The galaxy was discovered by astronomer William Herschel on December 30, 1783 and is a member of the Virgo Cluster. It is also classified as a LINER galaxy and as a Seyfert galaxy.NGC 4237 appears to be deficient in neutral atomic hydrogen (H I). This, combined with its large projected distance from M87 and its radial velocity close to the Virgo Cluster mean suggests that the galaxy may be on a highly radial orbit through the center of the cluster.

NGC 4298

NGC 4298 is a flocculent spiral galaxy located about 53 million light-years away in the constellation Virgo. The galaxy was discovered by astronomer William Herschel on April 8, 1784 and is a member of the Virgo Cluster.

NGC 4414

NGC 4414 is an unbarred spiral galaxy about 62 million light-years away in the constellation Coma Berenices. It is a flocculent spiral galaxy, with short segments of spiral structure but without the dramatic well-defined spiral arms of a grand design spiral. In 1974 a supernova, SN 1974G, was observed and was the only supernova in this galaxy to be recorded until June 7, 2013 when SN 2013df was discovered at Magnitude 14.

It was imaged by the Hubble Space Telescope in 1995, as part of the HST's main mission to determine the distance to galaxies, and again in 1999 as part of the Hubble Heritage project. It has been part of an ongoing effort to study its Cepheid variable stars. The outer arms appear blue due to the continuing formation of young stars and include a possible luminous blue variable with an absolute magnitude of −10.NGC 4414 is also a very isolated galaxy without signs of past interactions with other galaxies and despite not being a starburst galaxy shows a high density and richness of gas - both atomic and molecular, with the former extending far beyond its optical disk.NGC 4414 is a member of the Coma I Group, a group of galaxies lying physically close to the Virgo Cluster.

NGC 7083

NGC 7083 is a unbarred spiral galaxy located about 134 million light-years away in the constellation of Indus. It is also classified as a flocculent spiral galaxy. NGC 7083 was discovered by astronomer James Dunlop on August 28, 1826.

NGC 7793

NGC 7793 is a flocculent spiral galaxy about 12.7 million light-years away in the constellation Sculptor. It was discovered in 1826 by James Dunlop.

SSPSF model

The SSPSF (stochastic self-propagating star formation) model of star formation was proposed by Mueller & Arnett in 1976, generalized afterward by Gerola & Seiden in 1978 and Gerola, Seiden, & Schulman in 1980. This model proposes that star formation propagates via the action of shock waves produced by stellar winds and supernovae traversing the gas that composes the interstellar medium.

The Henize 206 nebula provides a clear example. In particular, 24μ infrared emission shows where a new generation of stars heats the remains of the supernova remnant that induced their formation.

In contrast to star formation in density-wave theories, which are limited to disk-shaped galaxies and produce global spiral patterns, SSPSF applies equally well to spirals, to irregular galaxies and to any local concentrations of gas in elliptical galaxies.

The effect may be envisioned as an "SIR infection model" in a differentially rotating disk, the host galaxy. The SIR model (perhaps most popularly familiar in the form of Conway's Game of Life) is applied to star formation propagating through the galaxy: Each generation of stars in a neighborhood includes some massive ones whose stellar winds and, soon, supernovae, produce shock waves in the gas (Susceptible material). These lead to collapsing nearby gas clouds, which produce the next generation of stars (Infection propagation); but in the immediate neighborhood, all initially available gas is used, so no further stars are born there for some period of time despite the shocks (Recovery from infection).

In a non-flattened galaxy, the infection would produce an outward propagating sphere. In a non-rotating flattened (disk) environment, the infection would produce an outward propagating ring. But in a differentially rotating flattened environment, i.e., with mass closer to the galactic center orbiting the center somewhat more quickly, the ring is sheared into an ellipse, the innermost parts moving ahead of the ring's center and the outermost parts lagging. For disk galaxies, virtually all star formation occurs in the disk. In that case, the elongated rings are likewise confined to the disk, and collectively they evolve to appear as (possibly disconnected) segments of spiral arms: See the example, as well as figures in.In 1999, the prevailing density wave model for the generation of spiral arms in galaxies was combined with SSPSF in a doctoral thesis by Auer (an idea first suggested by Gerola and Seiden in 1980). Auer concluded that density waves are in fact less effective in producing star formation, and more effective in simply organizing ongoing SSPSF into large-scale (spiral) patterns, ultimately into the Grand Design spiral form if conditions allow.

In the figure you can see a simulation of a simple model for SSPSF on a circular grid. It is generated by randomly starting star formation in certain boxes of the grid, which propagates to nearby boxes in the grid while time progresses. Star formation dies out with time and a box has a certain regeneration time which prevents it from starting new star formation just after it was active. Adding (differential) rotation to the disk during propagation creates spiral patterns that are of the same nature of those in actual spiral galaxies. Dark spots are areas of active star formation, lighter spots are areas of recent star formation/areas in regeneration.

SSPSF processes were demonstrated in an early prototype ("Gaslight") of the 2008 video game Spore.

Spiral galaxy

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.

Spiral galaxies are named by their spiral structures that extend from the center into the galactic disc. The spiral arms are sites of ongoing star formation and are brighter than the surrounding disc because of the young, hot OB stars that inhabit them.

Roughly two-thirds of all spirals are observed to have an additional component in the form of a bar-like structure, extending from the central bulge, at the ends of which the spiral arms begin. The proportion of barred spirals relative to their barless cousins has likely changed over the history of the Universe, with only about 10% containing bars about 8 billion years ago, to roughly a quarter 2.5 billion years ago, until present, where over two-thirds of the galaxies in the visible universe (Hubble volume) have bars.Our own Milky Way is a barred spiral, although the bar itself is difficult to observe from the Earth's current position within the galactic disc. The most convincing evidence for the stars forming a bar in the galactic center comes from several recent surveys, including the Spitzer Space Telescope.Together with irregular galaxies, spiral galaxies make up approximately 60% of galaxies in today's universe. They are mostly found in low-density regions and are rare in the centers of galaxy clusters.

Morphology
Structure
Active nuclei
Energetic galaxies
Low activity
Interaction
Lists
See also

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