The fact that there are other galaxies, astronomers knew already at the beginning of the XX century. Despite the fact that the first of the open galaxies were already known to scientists, at first they were called nebulae, attributing them to our galaxy - the Milky Way. Scientists assumed that these nebulae can represent separate stellar systems. However, such hypotheses could not withstand criticism from the scientific world. This was due to the imperfection of the technique for observation.
Studies of galaxies
In 1922, an astronomer from Estonia, Ernst Epic, was able to calculate the approximate distance that separates the solar system from the Andromeda nebula. The data that the astronomer received is 0.6 of the figures that scientists currently have - and this is even more accurate than that of E. Hubble. In 1924 Edwin Hubble himself used the largest telescope at that time. Its diameter was 254 cm. Hubble also made calculations of the distance to Andromeda. Now scientists have more accurate data, which are three times less than those made by Hubble - but still this distance is so great that the nebula can not be a part of our galaxy. So the Andromeda Nebula became the first separate galaxy.
Clusters of galaxies
Like stars, galaxies form groups of different numbers. In this case, this property is expressed in them much more than in stars. Most of the stars are not parts of the cluster, entering the common field of our galaxy. A group of galaxies that includes the Milky Way (local galaxy) has 40 galaxies. This grouping is very common in the expanses of the universe.
Galactic groups accessible for observation
The known part of the cluster of galaxies is called "Metagalaxy" - it can be observed with the help of astronomical methods. The Metagalaxy includes about one billion galaxies, the observation of which is accessible through telescopes. The Milky Way is one of the star systems that is part of the Metagalaxy. Our galaxy and still about 1.5 dozen galaxies are part of the galactic group, called the local group of galaxies.
The possibilities to explore the Metagalaxy appeared mainly at the end of the 20th century. Astronomers have found out that in intergalactic space there are cosmic and electromagnetic radiation, separate stars, and also intergalactic gas. Thanks to scientific achievements it became possible to study galaxies of different types - quasars, radio galaxies.
Properties of the Metagalaxy
Sometimes astronomers like to call the Metagalaxy of the "Great Universe". With the improvement of technology and telescopes, a large part of it becomes available for observation. Astronomers believe that the Milky Way and the nearest 10-15 galaxies are members of a single galaxy cluster. The metagalaxy is very common clusters of galaxies, the number of which is from 10 to several dozen members. Such groups are hardly distinguishable by astronomers at great distances. The reason is that dwarf galaxies are not accessible for observation, and giant in such groups, as a rule, only a few.
According to Einstein's theory of relativity, large masses are capable of curving space around themselves. Therefore, the positions of the Euclidean geometry in this space are not justified. Only on a huge scale of the Metagalaxy can we see the differences between the two scientific approaches - Newtonian mechanics and Einstein's mechanics. The Metagalaxy also operates the so-called law of redshift. This means that all galaxies around us are removed in different directions. And the further they are removed, the more their speed becomes.
Types of galaxies in shape
Galactic clusters can be scattered, or have a spherical shape. They can include dozens and even thousands of different galaxies. The galaxy closest to us is located in the constellation Virgo and is removed to a distance of 10 million parsecs. The clusters of galaxies, called regular, have a spherical shape. The galaxies entering into their composition tend to concentrate at one point - the center of the galaxy cluster. Right clusters are already characterized by a high density of galaxies, but at their center concentration reaches a maximum. However, there are the correct clusters and differences, manifested mainly in their density and different numbers of galaxies entering into their composition.
Galaxies with the highest density
For example, the group of galaxies of the Hair of Veronica is distinguished by a large number of components, and the galaxies that make up Pegasus are dense. It is especially high in the central region of Pegasus. Here the density reaches 2 thousand galaxies per 1 cubic megaparsec. Neighboring galaxies practically touch each other, and their density is almost 40,000 times higher than the density in the Metagalaxy. Also high density is characteristic of the groups of galaxies North Crown.
Where did the galaxies come from?
While scientists can not give an accurate answer to this question. However, according to the theory of the Big Bang, the young universe was full of hydrogen and helium. From this dense cloud, under the influence of dark matter (and subsequently the gravitational forces), the first stars and star clusters began to form.
When did the first stars appear in the universe?
According to some astronomers, the stars appeared early enough - already 30 million years after the Big Bang. Others are convinced that this figure is 100 million years. Studies using modern technology show that the luminaries were formed simultaneously for several pieces - often this number reached even hundreds. This contributed to the gravitational forces that affect the gas that filled the universe. Gas clouds spun into discs, and in them gradually formed seals, then became stars. In the young Universe, the first stars were really gigantic - they had a lot of "building material" for them.
The largest cluster of galaxies discovered by astronomers is called SPT-CL J0546-5345. Its mass is almost equal to the mass of 800 trillion Suns. To discover a giant galaxy, scientists were able to use the astronomical effect of Syunyaev-Zeldovich - it consists in the fact that the temperature of microwave radiation falls when it interacts with giant objects of the Universe. This cluster is 7 billion light-years away from us. In other words, astronomers observe it as it was 7 billion years ago - and this is 6.7 billion years after the Big Bang.
In the remote expanses of the universe, another cluster of galaxies was discovered that forms an isolated space system - ACT-CL J0102-4915. This huge group of galaxies astronomers nicknamed El Gordo, which in Spanish means "fat man." Its distance to the Earth is 9.7 billion light years. The mass of this group of galaxies exceeds the mass of the Sun in 3 million billion.
Hair of Veronica
Accumulation of Veronica's hair is one of the most interesting galactic groups in the Metagalaxy. It numbers about several thousand galaxies. They are located a few hundred million light-years from the Milky Way. Most galaxies are elliptical. The hair of Veronica is not distinguished by bright stars - even the alpha, called Diadema, is not large. In this constellation one can observe a cluster of luminous stars "Coma", which in Latin means "hair". Ancient Greek scientist Eratosthenes called this cluster "Ariadne's Hair." Ptolemy also attributed it to the composition of the star cluster of Leo.
One of the most beautiful galaxies of the constellation is NGC 4565, or "Needle". From the surface of our planet is visible from the edge. It is located 30 million light-years from the Sun. And the diameter of the galaxy is more than 100 thousand light years. In Veronica Hair, there are two interacting galaxies - NGC 4676, or, as this group is called, "Mice". They are 300 million light-years away from the Earth. Studies have shown that once already these galaxies passed through each other. Scientists suggest that "Mice" will face more than once, until they turn into a single galaxy.