Astronomers already knew about the existence of other galaxies at the beginning of the 20th century. Despite the fact that the first of the discovered galaxies were already known to scientists, at first they were called nebulae, attributing them to our galaxy - the Milky Way. Scientists have speculated that these nebulae may represent separate star systems. However, such hypotheses did not stand up to scrutiny from the scientific world. This was due to the imperfection of the observational technique.
Galaxy exploration
In 1922, Estonian astronomer Ernst Epik 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 numbers that scientists now have - and this is an even more accurate calculation than that of E. Hubble. Edwin Hubble himself in 1924 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 smaller than those made by Hubble - but still this distance is so large that the nebula cannot possibly be part of our galaxy. So the Andromeda Nebula became the first separate galaxy.
Clusters of galaxies
Like stars, galaxies form groups of different sizes. Moreover, this property is expressed in them to a much greater extent than in stars. Most of the stars are not part of the cluster, being part of the general field of our galaxy. The group of galaxies that includes the Milky Way (local galaxy) has 40 galaxies. This grouping is very common throughout the universe.
Group of galaxies available for observation
The known part of the cluster of galaxies is called "Metagalaxy" - it can be observed using astronomical methods. The composition of the Metagalaxy includes about one billion galaxies, the observation of which is available with the help of telescopes. The Milky Way is one of the star systems that is part of the Metagalaxy. Our galaxy and about 1.5 dozen other galaxies are part of a galactic group called the local group of galaxies.
Opportunities 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, individual stars, as well as intergalactic gas. Thanks to scientific advances, it has become possible to study galaxies of various types - quasars, radio galaxies.
Properties of the Metagalaxy
Sometimes astronomers like to call the Metagalaxy the "Big Universe". With the improvement of technology and telescopes, more and more of it becomes available for observation. Astronomers thinkthat the Milky Way and the next 10-15 galaxies are members of the same galaxy cluster. In the Metagalaxy, clusters of galaxies are very common, the number of which ranges from 10 to several dozen members. Such groups are poorly distinguishable by astronomers at large distances. The reason is that dwarf galaxies are not visible, and there are usually only a few giant galaxies in such groups.
According to Einstein's theory of relativity, large masses can bend space around them. Therefore, the provisions of Euclid's geometry in this space are not justified. Only on the vast scale of the Metagalaxy can one see the differences between the two scientific approaches - Newtonian mechanics and Einstein's mechanics. The so-called redshift law also operates in the Metagalaxy. This means that all the galaxies around us are receding in different directions. Moreover, the further they move away, the greater their speed becomes.
Types of galaxies by shape
Galactic clusters can be open or spherical. They can include dozens and even thousands of different galaxies. The closest galaxy to us is located in the constellation Virgo and is 10 million parsecs away. Clusters of galaxies, called regular, have a spherical shape. The galaxies that make up them tend to concentrate at one point - the center of the galactic cluster. Regular clusters already have a high densitygalaxies, but in their center the concentration reaches a maximum. However, regular clusters also have differences, manifested mainly in their density and the different numbers of their constituent galaxies.
The highest density galaxies
For example, the Coma of Veronica group of galaxies 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 thousand times higher than the density in the Metagalaxy. Also, high density is characteristic of the groups of galaxies in the Northern Corona.
Where did galaxies come from?
So far, scientists cannot give an exact answer to this question. However, according to the Big Bang theory, the young universe was full of hydrogen and helium. From this thick cloud, under the influence of dark matter (and subsequently 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 quite early - as early as 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 in several pieces - often this number even reached hundreds. This was facilitated by gravitational forces that affect the gas that filled the Universe. The gas clouds twisted into discs, and densifications gradually formed in them, then became stars. In the early Universe, the first stars were really gigantic in size - after all, there was 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. Scientists were able to detect a giant galaxy using the astronomical Sunyaev-Zeldovich effect - it lies in the fact that the temperature of microwave radiation drops when it interacts with giant objects in 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 far expanses of the Universe, another cluster of galaxies was discovered, forming a separate space system - ACT-CL J0102-4915. Astronomers have nicknamed this huge group of galaxies El Gordo, which means "fat man" in Spanish. Its distance to the Earth is 9.7 billion light years. The mass of this group of galaxies exceeds the mass of the Sun at 3 million billion.
Veronica's hair
The Coma Cluster is one of the most interesting galactic groups in the Metagalaxy. It contains about several thousand galaxies. They are located several hundred million light-years from the Milky Way. Majoritygalaxies are elliptical. Veronica's hair is not distinguished by bright stars - even the alpha, called the Tiara, is small. In this constellation, you can observe a cluster of faintly luminous stars "Coma", which in Latin means "hair". The ancient Greek scholar Eratosthenes called this cluster "Ariadne's Hair". Ptolemy attributed it to the Leo star cluster.
One of the most beautiful galaxies in the constellation is NGC 4565, or the Needle. From the surface of our planet, it is visible edge-on. It is located 30 million light years from the Sun. And the diameter of the galaxy is more than 100 thousand light years. There are also two interacting galaxies in the Hair of Veronica - NGC 4676, or, as this group is also called, "Mice". They are removed from the Earth at a distance of 300 million light years. Studies have shown that once these galaxies have passed through each other. Scientists suggest that the "Mice" will collide more than once, until they turn into one galaxy.
