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Spiral galaxy UGC 12591 is classified as an S0/Sa galaxy. [1]The Hubble sequence is a morphological classification scheme for galaxies invented by Edwin Hubble in 1926. [2] [3] It is often known colloquially as the “Hubble tuning-fork” because of the shape in which it is traditionally represented.
The giant elliptical galaxy ESO 325-4. 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, [1] along with spiral and lenticular galaxies.
The cD-type is a classification in the Yerkes galaxy classification scheme, one of two Yerkes classifications still in common use, along with D-type. [8] The "c" in "cD" refers to the fact that the galaxies are very large, hence the adjective supergiant, while the "D" refers to the fact that the galaxies appear diffuse. [9]
Elliptical and lenticular galaxies are commonly referred to together as "early-type" galaxies, while spirals and irregular galaxies are referred to as "late types". This nomenclature is the source of the common, [ 18 ] but erroneous, belief that the Hubble sequence was intended to reflect a supposed evolutionary sequence, from elliptical ...
Galaxies range in size from dwarfs with just a few billion (109) 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 and irregular. Many galaxies are thought to have black holes at their active centers.
Types of galaxies according to the Hubble classification scheme : an E indicates a type of elliptical galaxy; an S is a spiral; and SB is a barred spiral galaxy. Galaxies come in three main types: ellipticals, spirals, and irregulars. A slightly more extensive description of galaxy types based on their appearance is given by the Hubble sequence.
The first consists of elliptical galaxies that seem to be roughly as old as the universe. The second subpopulation contains red-sequence lenticular (lens shaped) galaxies whose ages are directly tied to their mass. The third and final subpopulation is of galaxies where star formation is still taking place, and are morphologically distributed. [9]
Massive elliptical galaxies have high Sérsic indices and a high degree of central concentration. This galaxy, M87, has a Sérsic index n~ 4. [4] Discs of spiral galaxies, such as the Triangulum Galaxy, have low Sérsic indices and a low degree of central concentration. Most galaxies are fit by Sérsic profiles with indices in the range 1/2 < n ...