Information about Elliptical Galaxy
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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.
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]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.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.It was once thought that the shape of ellipticals varied from spherical to highly elongated. 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:
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).
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.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.
Examples
See also
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.
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.
External links
- Elliptical Galaxies, SEDS Messier pages
- Elliptical Galaxies
A galaxy (from the Greek root γαλαξίας, meaning "milky", a reference to our own Milky Way) is a massive, gravitationally bound system consisting of stars, an interstellar medium of gas and dust, and dark matter.
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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,
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Edwin Hubble
Born November 20 1889
Marshfield, Missouri, U.S.
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Born November 20 1889
Marshfield, Missouri, U.S.
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19th century - 20th century - 21st century
1900s 1910s 1920s - 1930s - 1940s 1950s 1960s
1933 1934 1935 - 1936 - 1937 1938 1939
Year 1936 (MCMXXXVI
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1900s 1910s 1920s - 1930s - 1940s 1950s 1960s
1933 1934 1935 - 1936 - 1937 1938 1939
Year 1936 (MCMXXXVI
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The Hubble sequence is a morphological classification scheme for galaxies invented by Edwin Hubble in 1936.[1] It is often know colloquially as the Hubble tuning-fork because of the shape in which it is traditionally represented.
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STAR is an acronym for:
Organizations:
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Organizations:
- Society for Telescopy, Astronomy, and Radio, a non-profit astronomy club in New Jersey
- Special Tasks and Rescue or Special Tactics and Response, synonyms for SWAT
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globular cluster is a spherical collection of stars that orbits a galactic core as a satellite. Globular clusters are very tightly bound by gravity, which gives them their spherical shapes and relatively high stellar densities toward their centers.
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In astronomy, stellar evolution is the process by which a star undergoes a sequence of radical changes during its lifetime. Depending on the mass of the star, this lifetime ranges from hundreds of thousands to billions of years.
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interstellar medium (or ISM) is the name astronomers give to the gas and dust that pervade interstellar space. While the interstellar medium refers to the matter that exists between the stars within a galaxy, the energy, in the form of electromagnetic radiation, that
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Star formation is the process by which dense parts of molecular clouds collapse into a ball of plasma to form a star. As a branch of astronomy star formation includes the study of the interstellar medium and giant molecular clouds as precursors to the star formation process
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Galaxy groups and clusters are the largest gravitationally-bound objects. They form the densest part of the large scale structure of the Universe. In models for the gravitational formation of structure with cold dark matter, the smallest structures collapse first and eventually
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This article is about rotation as a movement of a physical body. For other uses, see Rotation (disambiguation).
A rotation is a movement of an object in a circular motion...... Click the link for more information.
interstellar medium (or ISM) is the name astronomers give to the gas and dust that pervade interstellar space. While the interstellar medium refers to the matter that exists between the stars within a galaxy, the energy, in the form of electromagnetic radiation, that
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Star formation is the process by which dense parts of molecular clouds collapse into a ball of plasma to form a star. As a branch of astronomy star formation includes the study of the interstellar medium and giant molecular clouds as precursors to the star formation process
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open cluster is a group of up to a few thousand stars that were formed from the same giant molecular cloud, and are still loosely gravitationally bound to each other. In contrast, globular clusters are very tightly bound by gravity.
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metallicity of an object is the proportion of its matter made up of chemical elements other than hydrogen and helium. (This terminology is used differently to the usual meaning of the word 'metal', since on the grandest of scales the universe is overwhelmingly composed of hydrogen
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globular cluster is a spherical collection of stars that orbits a galactic core as a satellite. Globular clusters are very tightly bound by gravity, which gives them their spherical shapes and relatively high stellar densities toward their centers.
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Galaxy groups and clusters are the largest gravitationally-bound objects. They form the densest part of the large scale structure of the Universe. In models for the gravitational formation of structure with cold dark matter, the smallest structures collapse first and eventually
..... Click the link for more information.
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Star formation is the process by which dense parts of molecular clouds collapse into a ball of plasma to form a star. As a branch of astronomy star formation includes the study of the interstellar medium and giant molecular clouds as precursors to the star formation process
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Star formation is the process by which dense parts of molecular clouds collapse into a ball of plasma to form a star. As a branch of astronomy star formation includes the study of the interstellar medium and giant molecular clouds as precursors to the star formation process
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spiral 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.
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parsec (symbol pc) is a unit of length used in astronomy. The length of the parsec is based on the method of trigonometric parallax, one of the oldest methods for measuring the distances to stars.
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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. There are at least two dE dwarf ellipticals in orbit around the Andromeda galaxy.
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globular cluster is a spherical collection of stars that orbits a galactic core as a satellite. Globular clusters are very tightly bound by gravity, which gives them their spherical shapes and relatively high stellar densities toward their centers.
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In astrophysics and cosmology, dark matter is 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.
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Messier object>Messier 87
Observation data: J2000 epoch
Constellation: Virgo
Right ascension: 12h 30m 49.
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Observation data: J2000 epoch
Constellation: Virgo
Right ascension: 12h 30m 49.
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New General Catalogue (NGC)
Spiral Galaxy NGC 3982 displays numerous spiral arms filled with bright stars, blue star clusters, and dark dust lanes. It spans about 30,000 light years, lies about 68 million light years from Earth and can be seen with a small telescope
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Spiral Galaxy NGC 3982 displays numerous spiral arms filled with bright stars, blue star clusters, and dark dust lanes. It spans about 30,000 light years, lies about 68 million light years from Earth and can be seen with a small telescope
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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,
..... Click the link for more information.
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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. There are at least two dE dwarf ellipticals in orbit around the Andromeda galaxy.
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Star clusters are groups of stars which are gravitationally bound. Two distinct types of star cluster can be distinguished: globular clusters are tight groups of hundreds of thousands of very old stars, while open clusters generally contain less than a few hundred members, and are
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