Citizendia
Your Ad Here

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. A galaxy is a massive gravitationally bound system consisting of Stars an Interstellar medium of gas and dust, and Dark matter Galaxy morphological classification is a system used by Astronomers to divide galaxies into groups based on their visual appearance Edwin Powell Hubble ( November 20, 1889 – September 28, 1953) was an American astronomer. Year 1936 ( MCMXXXVI) was a Leap year starting on Wednesday (link will display the full calendar of the Gregorian calendar. The Hubble sequence is a morphological classification scheme for Galaxies invented by Edwin Hubble in 1936 Elliptical galaxies have smooth, featureless light-profiles. They range in shape from nearly spherical to highly flattened ellipsoids and in size from hundreds of millions to over one trillion stars. An ellipsoid is a type of quadric surface that is a higher dimensional analogue of an Ellipse. A star is a massive luminous ball of plasma. The nearest star to Earth is the Sun, which is the source of most of the Energy on Earth In the outer regions, many stars are grouped into globular clusters. A globular cluster is a spherical collection of Stars that orbits a galactic core as a Satellite. Most elliptical galaxies are composed of older, low-mass stars, with a sparse interstellar medium and minimal star formation activity. Stellar evolution is the process by which a Star undergoes a sequence of radical changes during its lifetime Star Formation is the process by which dense parts of Molecular clouds collapse into a ball of plasma to form a Star. Elliptical galaxies are believed to make up approximately 10-15% of galaxies in the local Universe. The Universe is defined as everything that Physically Exists: the entirety of Space and Time, all forms of Matter, Energy [2] They are preferentially found close to the centers of galaxy clusters[3] and are less common in the early Universe. Galaxy groups and clusters are the largest Gravitationally bound objects to have arisen thus far in the process of cosmic structure formation

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. A rotation is a movement of an object in a circular motion A two- Dimensional object rotates around a center (or point) of 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. Star Formation is the process by which dense parts of Molecular clouds collapse into a ball of plasma to form a Star. An 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 In Astronomy and Physical cosmology, the metallicity of an object is the proportion of its matter made up of Chemical elements other than Hydrogen Large elliptical galaxies typically have an extensive system of globular clusters. A globular cluster is a spherical collection of Stars that orbits a galactic core as a Satellite. [4]

The properties of elliptical galaxies and the bulges of disk galaxies are similar, suggesting that they are formed by the same physical processes, although this remains controversial. Elliptical galaxies are preferentially found in the cores of galaxy clusters and in compact groups of galaxies. Galaxy groups and clusters are the largest Gravitationally bound objects to have arisen thus far in the process of cosmic structure formation

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. Star Formation is the process by which dense parts of Molecular clouds collapse into a ball of plasma to form a Star. Very little star formation is thought to occur. Star Formation is the process by which dense parts of Molecular clouds collapse into a ball of plasma to form a Star. 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. A 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

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. History The first direct measurements of an object at interstellar distances were undertaken by German Astronomer Friedrich Wilhelm Bessel in 1838 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. Dwarf elliptical galaxies, or dE's are elliptical galaxies that are much smaller than others classified as dE. A globular cluster is a spherical collection of Stars that orbits a galactic core as a Satellite. In Physics and cosmology, dark matter is hypothetical Matter that does not interact with the electromagnetic force but whose presence can be inferred from 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. Messier 87 (also known as M87, Virgo A or NGC 4486) is a giant Elliptical galaxy. The New General Catalogue ( NGC) is the best-known catalogue of Deep sky objects in Amateur astronomy.

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. Galaxy morphological classification is a system used by Astronomers to divide galaxies into groups based on their visual appearance 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:

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. Dwarf elliptical galaxies, or dE's are elliptical galaxies that are much smaller than others classified as dE. 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. Star clusters are groups of Stars which are gravitationally bound 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 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. Galaxy mergers can occur when two (or more galaxies collide They are the most violent type of galaxy interaction.

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. The Milky Way (a translation of the Latin Via Lactea, in turn derived from the Greek Γαλαξίας (Galaxias sometimes referred to simply

Examples

See also

References

  1. ^ Hubble, E. P. (1936). The Hubble sequence is a morphological classification scheme for Galaxies invented by Edwin Hubble in 1936 The Galaxy color-magnitude diagram shows the relationship between Absolute magnitude, Luminosity, and Mass of Galaxies. Galaxy morphological classification is a system used by Astronomers to divide galaxies into groups based on their visual appearance A lenticular galaxy is a type of Galaxy which is intermediate between an Elliptical galaxy and a Spiral galaxy in Galaxy morphological classification Edwin Powell Hubble ( November 20, 1889 – September 28, 1953) was an American astronomer. 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.  
  3. ^ Dressler, A. (March 1980). "Galaxy morphology in rich clusters - Implications for the formation and evolution of galaxies.". The Astrophysical Journal 236: 351-365. doi:10.1086/157753. A digital object identifier ( DOI) is a permanent identifier given to an Electronic document.  
  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. Year 2007 ( MMVII) was a Common year starting on Monday of the Gregorian calendar in the 21st century. Events 618 - Coronation of the Chinese governor Li Yuan as Emperor Gaozu of Tang, the new Emperor of China, initiating three centuries

External links

Dictionary

elliptical galaxy

-noun

  1. A galaxy having a smooth, featureless light-profile. It is one of the three main classes of galaxies originally described by Edwin Hubble in his 1936 work “The Realm of the Nebulae”.
© 2009 citizendia.org; parts available under the terms of GNU Free Documentation License, from http://en.wikipedia.org
 Dapyx Software network: MP3 Explorer | Ebook Manager | Zenithic