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Encyclopedia > Elliptical galaxy
The giant elliptical galaxy ESO 325-G004.
The giant elliptical galaxy ESO 325-G004.

An elliptical galaxy is a galaxy belonging to one of the three main classes of galaxy originally described by Edwin Hubble in his 1936 work “The Realm of the Nebulae”[1] and, as such, forms part of the Hubble sequence. Elliptical galaxies have smooth, featureless light-profiles and range in shape from nearly spherical to highly flattened, and in size from hundreds of millions to over one trillion stars. In the outer regions, many stars are grouped into globular clusters. Most elliptical galaxies are composed of older, low-mass stars, with a sparse interstellar medium and minimal star formation activity. Elliptical galaxies are believed to make up approximately 10-15% of galaxies in the local Universe.[2] They are preferentially found close to the centers of galaxy clusters[3] and are less common in the early Universe. Image File history File links Metadata Size of this preview: 560 × 600 pixelsFull resolution (2759 × 2956 pixel, file size: 1. ... Image File history File links Metadata Size of this preview: 560 × 600 pixelsFull resolution (2759 × 2956 pixel, file size: 1. ... For other uses, see Galaxy (disambiguation). ... Astronomers classify galaxies based on their overall shape (elliptical, spiral or barred spiral) and further by the specific properties of the individual galaxy (for example degree of ellipse, number of spirals or definition of bar). ... Edwin Powell Hubble (November 20, 1889 – September 28, 1953) was an American astronomer. ... 1936 (MCMXXXVI) was a leap year starting on Wednesday (link will take you to calendar). ... It has been suggested that this article or section be merged with Galaxy classification. ... STAR is an acronym for: Organizations Society of Ticket Agents and Retailers], the self-regulatory body for the entertainment ticket industry in the UK. Society for Telescopy, Astronomy, and Radio, a non-profit New Jersey astronomy club. ... The Globular Cluster M80 in the constellation Scorpius is located about 28,000 light years from the Sun and contains hundreds of thousands of stars. ... In astronomy, stellar evolution is the sequence of radical changes that a star undergoes during its lifetime (the time in which it emits light and heat). ... The interstellar medium (or ISM) is the name astronomers give to the tenuous gas and dust that pervade interstellar space. ... Media:Example. ... Galaxy groups and clusters are super-structures in the spread of galaxies of the cosmos. ...

Contents

General characteristics

Elliptical galaxies are characterized by several properties that make them distinct from other classes of galaxy. The motion of stars in elliptical galaxies is predominantly radial, unlike the disks of spiral galaxies, which are dominated by rotation. Furthermore, there is very little interstellar matter (neither gas nor dust), which results in low rates of star formation, few open star clusters, and few young stars; rather, elliptical galaxies are dominated by old stellar populations, giving them red colours. Large elliptical galaxies typically have an extensive system of globular clusters.[4] A sphere rotating around its axis. ... The interstellar medium (or ISM) is a term used in astronomy to describe the rarefied gas and dust that exists between the stars (or their immediate circumstellar environment) within a galaxy. ... Media:Example. ... The Pleiades is one of the most famous open clusters. ... Stars can be grouped into two general types called Population I and Population II. The criteria for classification include space velocity, location in the galaxy, age, chemical composition, and differences in distribution on the Hertzsprung-Russell diagram. ... The Globular Cluster M80 in the constellation Scorpius is located about 28,000 light years from the Sun and contains hundreds of thousands of stars. ...


The properties of elliptical galaxies and the bulges of disk galaxies are similar, suggesting that they are formed same physical processes, although this remains controversial. Elliptical galaxies are preferentially found in the cores of galaxy clusters and in compact groups of galaxies. ...


Star formation

This traditional portrait of elliptical galaxies paints them as galaxies where star formation has finished after the initial burst, leaving them to shine with only their aging stars. Very little star formation is thought to occur. In general, they appear yellow-red, which is in contrast to the distinct blue tinge of a typical spiral galaxy, a colour emanating largely from the young, hot stars in its spiral arms. Media:Example. ... Media:Example. ... It has been suggested that spiral nebula be merged into this article or section. ...


Sizes and shapes

There is a wide range in size and mass for elliptical galaxies: as small as a tenth of a kiloparsec to over 100 kiloparsecs, and from 107 to nearly 1013 solar masses. This range is much broader for this galaxy type than for any other. The smallest, the Dwarf elliptical galaxies, may be no larger than a typical globular cluster, but contain a considerable amount of dark matter not present in clusters. Most of these small galaxies may not be related to other ellipticals. The single largest known galaxy, M87 (which also goes by the NGC number 4486), is an elliptical. This article is about the unit of length. ... Dwarf elliptical galaxies are elliptical galaxies that are much smaller than others, classified as dE. They are quite common, and are usually companions to other galaxies. ... The Globular Cluster M80 in the constellation Scorpius is located about 28,000 light years from the Sun and contains hundreds of thousands of stars. ... In astrophysics and cosmology, dark matter refers to hypothetical matter of unknown composition that does not emit or reflect enough electromagnetic radiation to be observed directly, but whose presence can be inferred from gravitational effects on visible matter. ... The jet emitted by M87 in this image is thought to be caused by a supermassive black hole at the galaxys center. ... The New General Catalogue (NGC) is the most well-known catalogue of deep sky objects in amateur astronomy. ...


It was once thought that the shape of ellipticals varied from spherical to highly elongated.[citation needed] The Hubble classification of elliptical galaxies ranges from E0 for those that are most spherical, to E7, which are long and thin in profile. It is now recognized that the vast majority of ellipticals are of middling thinness, and that the Hubble classifications are a result of the angle with which the galaxy is observed. The classification is typically determined by the ratio of the major (a) to the minor (b) axes of the galaxy's elliptical profile as follows: Astronomers classify galaxies based on their overall shape (elliptical, spiral or barred spiral) and further by the specific properties of the individual galaxy (for example degree of ellipse, number of spirals or definition of bar). ...

10 times (1 - frac{b}{a})

Thus for a spherical galaxy with a equal to b, the number is 0. The limit is about 7, which may indicate a physical process that prevents further flattening.[5]


There are two physical types of ellipticals; the "boxy" giant ellipticals, whose shapes result from random motion which is greater in some directions than in others (anisotropic random motion), and the "disky" normal and low luminosity ellipticals, which have nearly isotropic random velocities but are flattened due to rotation.


Dwarf elliptical galaxies are probably not true ellipticals at all; they have properties that are similar to those of irregulars and late spiral-type galaxies. Many astronomers now refer to them as "dwarf spheroidals" in recognition of this (note that this is still a topic of some controversy). Dwarf elliptical galaxies are elliptical galaxies that are much smaller than others, classified as dE. They are quite common, and are usually companions to other galaxies. ...


Role in galactic evolution

Some recent observations have found young, blue star clusters inside a few elliptical galaxies along with other structures that can be explained by galactic collisions. Current thinking is that an elliptical galaxy is the result of a long process where two galaxies of comparable mass, of any type, collide and merge. This article or section does not cite its references or sources. ... In astrophysics, the questions of galaxy formation and evolution are: How, from a homogeneous universe, did we obtain the very heterogeneous one we live in? How did galaxies form? How do galaxies change over time? A spectacular head-on collision between two galaxies is seen in this NASA Hubble Space...


Such major galactic mergers are thought to have been common at early times, but may carry on more infrequently today. Minor galactic mergers involve two galaxies of very different masses, and are not limited to giant ellipticals. For example, our own Milky Way galaxy is known to be "digesting" a couple of small galaxies right now. For other uses, see Milky Way (disambiguation). ...


Examples

Elliptical Galaxy M32 (also known as Messier Object 32, Messier 32, M32, or NGC 221) is a dwarf elliptical galaxy in the Andromeda constellation, a satellite of the Andromeda Galaxy, and a member of the Local Group galaxies. ... Elliptical Galaxy M49 (also known as Messier Object 49, Messier 49, M49, or NGC 4472) is an elliptical galaxy in the Virgo constellation. ... M59, courtesy of NOAO. Elliptical Galaxy M59 (also known as Messier Object 59, Messier 59, M59, or NGC 4621) is an elliptical galaxy in the constellation Virgo. ... M60, courtesy of NOAO Elliptical Galaxy M60 (also known as Messier Object 60, Messier 60, M60, or NGC 4649) is an elliptical galaxy in the constellation Virgo. ... The jet emitted by M87 in this image is thought to be caused by a supermassive black hole at the galaxys center. ... Elliptical Galaxy M89 (also known as Messier Object 89, Messier 89, M89, or NGC 4552) is an elliptical galaxy in the Virgo constellation. ... Elliptical Galaxy M105 (also known as Messier Object 105, Messier 105, M105, or NGC 3379) is an elliptical galaxy in the Leo constellation. ... The Elliptical Galaxy M110 (also known as Messier Object 110, Messier 110, M110, or NGC 205) is an elliptical galaxy in the Andromeda constellation, a satellite of the Andromeda Galaxy, and a member of the Local Group galaxies. ...

See also

It has been suggested that this article or section be merged with Galaxy classification. ... Astronomers classify galaxies based on their overall shape (elliptical, spiral or barred spiral) and further by the specific properties of the individual galaxy (for example degree of ellipse, number of spirals or definition of bar). ... The Spindle Galaxy (NGC 5866), a lenticular galaxy in the Draco constellation. ...

References

  1. ^ Hubble, E. P. (1936). The Realm of the Nebulae. New Haven: Yale University Press. ISBN 36018182. 
  2. ^ Loveday, J. (February 1996). "The APM Bright Galaxy Catalogue.". Monthly Notices of the Royal Astronomical Society 278 (4): 1025-1048. Retrieved on 2007-09-15. 
  3. ^ Dressler, A. (March 1980). "Galaxy morphology in rich clusters - Implications for the formation and evolution of galaxies.". The Astrophysical Journal 236: 351-365. Retrieved on 2007-09-15. 
  4. ^ Binney, J.; Merrifield, M. (1998). Galactic Astronomy. Princeton: Princeton University Press. ISBN 9780691025650. 
  5. ^ Keel, Bill (August 2006). Galaxy Classification. The University of Alabama. Retrieved on 2007-06-18.

Edwin Powell Hubble (November 20, 1889 – September 28, 1953) was an American astronomer. ... Year 2007 (MMVII) is the current year, a common year starting on Monday of the Gregorian calendar and the AD/CE era in the 21st Century. ... is the 258th day of the year (259th in leap years) in the Gregorian calendar. ... Year 2007 (MMVII) is the current year, a common year starting on Monday of the Gregorian calendar and the AD/CE era in the 21st Century. ... is the 258th day of the year (259th in leap years) in the Gregorian calendar. ... Year 2007 (MMVII) is the current year, a common year starting on Monday of the Gregorian calendar and the AD/CE era in the 21st Century. ... is the 169th day of the year (170th in leap years) in the Gregorian calendar. ...

External links

Wikimedia Commons has media related to:
Category:Elliptical galaxies

  Results from FactBites:
 
elliptical galaxy (533 words)
Giant ellipticals, such as M87, may contain over 10 trillion solar masses in the form of stars, are among the largest of galaxies, and are often found at the heart of rich clusters of galaxies.
Dwarf ellipticals, on the other hand, such as M32 (a satellite of the Andromeda Galaxy) may have masses as low as 10 million solar masses and lie at the bottom end of the galactic size range.
It used to be thought that ellipticals were the oldest galaxies, but more recent studies, including computer simulations, suggest that they have formed from collisions and mergers between spiral galaxies.
Elliptical galaxy - Wikipedia, the free encyclopedia (610 words)
This traditional portrait of elliptical galaxies paints them as galaxies where the star formation was over after the initial burst, now shining only with their aging stars.
Dwarf elliptical galaxies are probably not true ellipticals at all; they have properties that are similar to those of irregulars and late spiral-type galaxies.
Elliptical galaxies tend to lie in the cores of galaxy clusters and in compact groups of galaxies.
  More results at FactBites »

 
 

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