Those who like to look at the starry night sky must have noticed a wide band densely strewn with a variety of (bright, slightly noticeable, blue, white, etc.) stars. This cluster is the galaxy.
What are galaxies? One of the greatest secrets of the Universe is that countless stars are not randomly scattered in outer space, but are grouped into galaxies. In almost the same way as people populate cities, leaving the space between settlements empty.
Our planet enters the Milky Way galaxy. Some names of galaxies are well known to us: Big and Small Magellanic clouds, Andromeda nebula. We can examine them with the naked eye, while others are very far removed from the Earth. For quite a long time, it was not possible to consider individual stars in them, it turned out to be done only in the 20th century.
"What are galaxies?" - This question has interested scientists for a long time. But a real breakthrough in this area occurred at the end of the twentieth century, when the Hubble telescope was created and launched into space.
The dimensions of our galaxy are so huge that it is impossible to even imagine. One hundred thousand Earth years will be required for a light ray to get from one of its edges to another. In its center is the core, from which several spiral-shaped lines filled with stars branch. This "density" is only apparent, in fact they are located quite rarely.
Different types of galaxies are known. They vary in shape, weight, size, and also in the substances contained in them. All of them contain gas and stardust. There are spiral, elliptical, irregular, sphere-like and other forms of galaxies.
What are galaxies? What is their age? How are they arranged? What processes are taking place in them? Their age is approximately equal to the age of the Universe. For scientists, it remains a mystery what the core of the galaxy is. It was found that some nuclei are quite active. This was a surprise, because before this discovery it was believed that the core is a dense cluster of hundreds of millions of stars. Radiation (both optical and radio) can change in some galactic nuclei over several months. This means that they release a tremendous amount of energy (much more than during a supernova flash) in a short time.
In 1963, completely new objects were discovered that have a star-shaped appearance. They were called quasars. Their luminosity, as it turned out later, far exceeds the luminosity of galaxies. Surprisingly, the brightness of quasars can vary.
The formation of galaxies is a natural process of evolution of the Universe, proceeding under the influence of gravitational forces. The variety of species and forms of galaxies is explained by the variety of conditions in which they originated. Galaxy compression can last 3 billion years. At this time, the gas transforms into a stellar system. It is by compressing the gas cloud that stars are formed (upon reaching a certain density and temperature sufficient for thermonuclear processes).
Gradually, the reserves of interstellar gas are depleted, and the formation of stars becomes less intense. When all resources are exhausted, the spiral galaxy is transformed into a lenticular, consisting entirely of red stars. This stage goes through elliptical galaxies, whose gas resources were used up 15-20 billion years ago.
Many people have an idea of what galaxies are formed from numerous science fiction films whose heroes adore traveling through space, visiting unknown planets and galaxies. In fact, this is not foreseen in the foreseeable future. Even if we move at the speed of light (which is also impossible yet), then we will reach the Andromeda Nebula (the nearest galaxy to us) only after 2.5 million years. Although (according to astronomers' calculations) it is approaching us and in 4-5 billion years it will collide with our Milky Way, which will lead to the formation of a new elliptical galaxy.
