It should be noted that galaxies are the main structural components of the universe, which contain almost all of its substance that radiates in the visible area of the spectrum. Stars are born and die in galaxies, and planetary systems are formed around them. The purpose of this paper is to discuss the nature of galaxies and determine the frequency of galaxy types and their distribution.
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Nature of Different Galaxies
Experts in the field believe that most of the galaxies of the universe have a spiral structure. The appearance and characteristics of galaxies are very diverse, and sizes vary from a few hundred parsecs to hundreds of kiloparsecs. In general, galaxies can be divided into several groups, which are elliptical, spiral, and irregular (Silva et al. 2). In the first case, the galaxies are smooth, structureless, ellipsoidal systems. In the second case, the galaxies have developed spiral arms, and in the third instance, they have a chaotic, irregular shape and no central bulge.
In addition to stars, galaxies contain a significant amount of both atomic and molecular gas and dust, while space is penetrated by cosmic rays and magnetic fields. At present, it is known that galaxies are more massive than it has been expected (Silva et al. 2). Also, it should be stressed that a detailed study of the rotation and stability of galactic subsystems allowed deriving an idea of the massive invisible (dark) halos surrounding galaxies. By their size, they are much more extended and may contain a significant part of the mass of galaxies immersed in them.
Interestingly, the presence of the bar depends on how the mass is distributed, that is, whether it is concentrated in the center or evenly distributed across the galaxy. Studies of the development of galaxies suggest that their evolution proceeds in the direction from less twisted to more twisted structures (Kuminski and Shamir 1). Moreover, the fibrous structure of the universe serves as the rationale for the fact that galaxies form chains.
Frequency and Distribution of Galaxies
The distribution of galaxies in the universe is extremely uneven, and most of them are gathered in clusters. Although galaxies are randomly spread, standard candles are utilized to determine their frequency and distribution. It is crucial that clusters are diverse in characteristics, but they can be divided into regular and irregular ones. In both instances, galaxies are gravitationally bound by mutual attractions (Silva et al. 2).
Regular clusters of galaxies have a spherical shape, and they are immense (they include thousands of galaxies most of which are elliptical or lenticular in nature). One or two giant elliptical galaxies occupy the center of the cluster. In a regular cluster, galaxies move relative to each other at speeds of about a thousand kilometers per second.
In irregular clusters, galaxies of all types may be found. They have an irregular shape and have separate condensations within the cluster. In 30,000,000 light years of the Milky Way, most frequently observed type is the irregular galaxies (Cava et al. 10). Curiously, most of them are low luminosity (due to their irregular nature). Its local neighborhood consists of 50 galaxies (which is a rather small number), and the major objects are within one megaparsec. The Local Group includes such galaxy types as spirals, irregulars, and dwarf ellipticals.
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Thus, it can be concluded that the nature of galaxies observed in the universe is diverse. As a rule, they are divided into three main categories, which are elliptical, spiral, and irregular galaxies. In addition, the distribution of galaxies does not follow a specific pattern. Nevertheless, most of the systems form either regular or irregular clusters. The frequency of galaxies should be researcher further since many aspects of this issue are still not studied enough.
Cava, Antonio, et al. “Structural and Dynamical Modeling of WINGS Clusters. I. The Distribution of Cluster Galaxies of Different Morphological Classes within Regular and Irregular Clusters.” Astronomy & Astrophysics, vol. 606, no. A108, 2017, pp. 1-11.
Kuminski, Evan, and Lior Shamir. “A Computer-Generated Visual Morphology Catalog Of 3,000,000 SDSS Galaxies.” The Astrophysical Journal Supplement Series, vol. 223, no. 2, 2016, pp. 1-10.
Silva, Pedro, et al. “SpArcFiRe: Enhancing Spiral Galaxy Recognition Using Arm Analysis and Random Forests.” Galaxies, vol. 6, no. 3, 2018, pp. 1-19.