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Globular clusters draw the attention of many scientists worldwide because they can contribute consistently to the research of space and better understanding of the formation, development and evolution of stars and galaxies at large. In fact, the question of formation and evolution of galaxies and universe is one of the major challenges of modern astronomy and many specialists (Baumgardt, 2003) believe that globular clusters can help find possible answers to the question concerning the origin and development of the universe. At the same time, globular clusters also represent a subject of a profound interest of scientists because of their uniqueness. It should be pointed out that they are quite different from other star formations and, what is probably even more important, is the fact that they are much older than galactic or open clusters. In this respect, it should be said that the age of globular clusters makes their research also very important because, being older than some other star formations, globular clusters can naturally provide scientists with larger information about the process of formation development of stars, galaxies and the universe at large. In such a way, the research of globular clusters may be considered very perspective, taking into consideration their actual and potential significance for the further researches of space.
The basic properties of globular clusters
First of all, it is necessary to dwell upon the basic characteristics and properties of globular clusters and the definition of the concept of globular clusters, in order to better understand their significance for modern science as well as their uniqueness in the universe that naturally provokes a profound interest of scientists. In this respect, it should be said that globular clusters are spherical collections of stars that orbits galactic core as satellites (Shapley, 1987). This means that a globular cluster represents a group or collection of stars that are situated in a galaxy and orbit its core. In fact, they are closely linked to the orbit core and keep in together due to the force of gravity which prevents them from distancing from each other and abandoning their orbit. Otherwise, they would simply left the orbit and instead of keeping within the globular cluster stars would simply travel throughout the universe that naturally contradicts to the basic physical laws, taking into consideration the grouping and structure of globular clusters.
It should be pointed out that globular clusters are not only closely bounded by their gravity, but due to the gravity they actually have acquired their spherical form. The remarkable property of globular clusters is their relatively high stellar density toward their centers. In fact, their name “globular” means spherical because the word “globular” originates from Latin word designating a small sphere.
Unlike galactic, or open clusters, globular clusters are more dense and have a large number of stars. Nowadays, there are about 150 globular clusters known to the modern science, though, it is quite logical to presuppose that the number of globular clusters may increase in the course of the research of the universe. According to the forecast of specialists, large galaxies, such as Andromeda may have 500 globular clusters, while giant ecliptic galaxies may have more than 10.000 globular clusters (Finley, 2007).
Furthermore, it is worthy of mention the fact that some globular clusters contain some of the first stars produced in the galaxy. This means that globular clusters contain very old stars. In fact, globular clusters are basically composed of such old, low-metal stars, which may count as much as hundreds of thousands. In such a way, it is obvious that globular clusters represent huge clusters of old stars. Specialists estimate that they are free of gas and dust which turned into stars and the density of stars is very high to the extent that it may reach 0.4 stars per cubic parsec (Baumgardt, 2003). Moreover, in the core of a globular cluster the density of stars may reach 100 or even 1000 stars per cubic parsec (Baumgardt, 2003).
At the same time, it is believed that planetary systems are not developed in globular clusters because they cannot provide planetary systems with the stability that are needed for their development and normal functioning. In fact, specialists argue that planetary systems cannot simply survive in globular clusters because of the high perturbations of passing stars (Shapley, 1987). The latter is apparently provoked by the high density of globular clusters. Although, it does not necessarily exclude the probability of the existence of planetary systems in globular clusters. At any rate, one of such systems has been already found orbiting a pulsar belonging to the globular cluster M4 (Baumgardt, 2003), but such cases are rather exceptional than common because of the physical peculiarities of globular clusters, mainly high density of stars, the conditions for the development of planetary systems are not good.
Also, it should be said that among all globular clusters, it is possible to single out supermassive globular clusters which represent a particular interest for scientists because they may contain several stellar populations and have several million solar masses (Finley, 2007). In fact, such supermassive globular clusters are cores of dwarf galaxies that are consumed by large galaxies. Moreover, researchers estimate that globular clusters have extremely massive cores which may harbor black holes, though simulation suggests that a less massive black hole or central concentration f neutron stars or massive white dwarfs explain observations equally well (Baumgardt, 2003). Nevertheless, such a potentially ability of globular clusters to harbor black holes is very important and needs to be thoroughly researched because black holes are one of the major mysteries of the universe and their link to globular clusters may contribute to better understanding of the phenomenon of black holes in the result of the further researches of globular clusters.
The location of globular clusters
In fact, globular clusters are widely spread and it is possible to estimate that they are present in the majority of galaxies. At the same time, it is necessary to underline that they are located in the core of galaxies. To put it more precisely, globular clusters orbit the core of galaxies and actually, they may be viewed as the inner part of galaxies. It is worthy of mention the fact that the number of globular clusters may vary depending on the size of galaxies since they may vary from few to hundreds and even thousands in particular large and gigantic galaxies.
Furthermore, the location of globular clusters in the core of galaxies is basically determined by their high density and indicates to the fact that they were among the first star formation in galaxies because the probability of the formation of stars near the core of a galaxy is considerably higher than at the larger distance from the core. The reason for such a trend is quite obvious since the density of elements and material, including gases, that actually form stars is higher near the core of galaxies that at a distance.
In general, it should be said that the location of globular clusters in galaxies is similar. This means that in different galaxies globular clusters tend to be located in the similar parts of galaxies, i.e. near the core. This may be viewed as evidence of the similarity of their formation and development that implies that their formation and development is common to all galaxies and may be viewed as a kind of a common trend or rule in the evolution of globular clusters.
The age of globular clusters
As it has been already mentioned above, globular clusters often include the first stars of the galaxies and, in general, old stars basically dominate in the structure of globular clusters. In such a way, it is possible to estimate that globular clusters are really old. At any rate, it is practically an undeniable fact that globular clusters are consistently older than galaxy, or open clusters. At the same time, the analysis of color-magnitude diagrams is often very helpful in the process of definition of the age of globular clusters.
In this respect, it should be said that the analysis of color-magnitude diagram provides a researcher with the information concerning the chemical structure of stars constituting globular clusters and the chemical structure of globular clusters at large. The analysis of the specter helps define this chemical structure, while on the basis of the latter it is possible to define the approximate age of globular clusters. It should be said that the fact that globular clusters contain predominantly low-metal stars proves the fact that the stars are quite old and so are globular clusters.
At the same time, on analyzing the age of globular clusters, researchers have found a very noteworthy fact. To put it more precisely, they found that each globular cluster have a definite age (Finley, 2007). In actuality, this means that stars comprising globular clusters were formed and developed in a definite age. Consequently, they represent grouping of stars that are of approximately similar age. In such a situation, it is necessary to underline that due to such a similarity in the age of stars, they are at approximately the same stage in stellar evolution.
Moreover, it is necessary to underline that globular clusters are considered to be the oldest objects in a galaxy (Baumgardt, 2003). In fact, stars comprising a globular cluster were among the first stars that appeared in a galaxy, while globular clusters were among the first star collections to form in the galaxy. Another evidence of the old age of globular clusters is the fact that all known globular clusters appear to have no active star formation (Baumgardt, 2003). Basically, this means that the growth and development of globular clusters has already stopped because there are only old stars and there are no new stars. Consequently, gradually stars constituting globular clusters will grow older until the moment of their destruction and eventually this will naturally lead to the gradual decline and even disappearance of globular clusters in the future.
In such a way, globular clusters represent probably the oldest star formations in the universe and this fact is very important in terms of the research of the universe and its evolution.
The contribution of globular clusters in understanding of structure, formation, and evolution of galaxies
In fact, globular clusters traditionally represent a subject of a particular concern of scientists because of its great significance for the research of the development and evolution of galaxies. It is not a secret that human knowledge about the formation and development of galaxies and the universe at large are quite scarce and it is very important to have some material that could reveal the mystery of the past, the mystery of the evolution of galaxies and the universe. Taking into consideration the old age of globular clusters they may be very helpful in understanding the evolution of galaxies because they actually indicate to the future development of new stars and new star formations, which, in all probability, will undergo the similar process of change as stars constituting globular clusters have already undergone.
Nevertheless, it is not only the current stage of the evolution and development of globular cluster that is important to research in order to better understand the evolution of galaxies, but it is also necessary to understand the origin of globular clusters. In this respect, it should be pointed out that specialists (Finley, 2007) have certain suggestions concerning the origin of globular clusters and the way of their formation. Taking into consideration the fact that globular clusters comprise predominantly old stars and do not have any active formation processes, it would be logical to research new stars and new star formation to understand the ways in which globular clusters were formed and their origin. In such a context, it is worthy of mention that some scientists stand on the ground that large regions of star formation known as super star clusters are precursors of globular clusters (Baumgardt, 2003).
Such a presupposition is actually quite logical. At any rate, it supports the idea of the gradual evolution of stars and star formations and it is obvious that at the early stages of the development, globular clusters could resemble the modern super star clusters which are predominantly formed by new stars and where the process of new formations are very active. In such a way, it is possible to presuppose that initially globular clusters were formed on the basis of the stars that were formed near the core of galaxies. As it has been already mentioned above, due to the higher density of various elements and materials, which are actually used for the formation of stars, near the core of galaxies, it is quite logical that the first stars appeared there. Gradually, the number of stars increased in the course of the development of galaxies. Consequently, the density of stars increased proportionally to the increasing number of stars near the core. Eventually, the number of stars and their density became critical to the extent that they started to form the clusters, which are now defined as globular clusters. These clusters were formed under the impact of gravity that influenced numerous stars located near the core of galaxies. As a result, stars orbiting the core were united into the cluster under the impact of mutual influence and the influence of the core determined by gravity.
In such a way, globular clusters could evolve from the first stars to the formation of clusters, until the present moment when globular cluster represent stellar formation comprised by old stars. At the same time, the further development of globular clusters and, therefore, galaxies, since globular clusters orbit the core of galaxies and actually create its basis, is quite unclear. In fact, it is quite difficult to forecast definitely the further development of globular clusters and galaxies because globular clusters are the oldest star formation. This is why there are practically no other source of information about the late or probably final stages of the development of such clusters. Naturally, it is possible to presuppose that they will gradually be destructed as do old stars and it is obvious that the destruction of globular clusters will affect dramatically the further development of galaxies, to the extent that it is just possible to presuppose that galaxies could be totally reshaped in the future.
Thus, taking into account all above mentioned, it is possible to conclude that globular clusters are one of the oldest stellar formations in galaxies that make them particularly interesting to scientist because their research may help understand the process of formation, development and evolution of galaxies. At the same time, in spite of all the progress of the modern science, globular clusters still remain under-researched and there are a lot of questions concerning the formation, development and evolution that remain unanswered, such as the possible interaction between globular clusters and black holes, the future of globular clusters and galaxies, and many others.