Looking into the deepest space with telescopes such as the Hubble, we see billions and billions of galaxies of various shapes and sizes. There are hundreds of billions of galaxies in the Universe, each galaxy has hundreds of billions of stars, and many of them have planets. The universe is constantly expanding and the distances between galaxies are constantly increasing. The further away the Galaxy is, the faster it moves away.
The universe stretches in space endlessly. Stars visible to the naked eye account for a tiny fraction of all stars. We see about 5,000 stars in the sky - just about 0.0001% of all stars in our Galaxy. If a star were a grain of salt, all the stars visible to the naked eye would fit in a teaspoon, and the stars of the entire universe would make up a ball more than thirteen kilometers in diameter.
We live on a planet orbiting a medium-sized yellow star, the Sun, at the inner edge of the Orion Arm, the Milky Way's spiral galaxy. The diameter of our Galaxy is about a hundred thousand light years! The light of very distant stars has not yet reached us. The galaxy rotates slowly, and the stars in its spiral arms make approximately one revolution around the center in one hundred million years.
A supermassive black hole, Sagittarius A, was discovered in the center of the Galaxy, the mass of which is a million times the mass of the Sun. The center of the galactic nucleus is in the constellation Sagittarius. For a long time it was believed that the Milky Way is the entire universe. And only in 1924, astronomer Edwin Hubble showed that our Galaxy is not the only one. There are many other galaxies, separated by giant swaths of empty space.
Interstellar dust in the spiral arms of the Milky Way makes it difficult to observe the Universe near the galactic plane. It seems that the density of galaxies at very large distances decreases, but, most likely, due to their distance, their light becomes so weak that they cannot be detected. Scientists can determine distances to nearby stars by recording changes in their position in the firmament as the Earth revolves around the Sun. But, unlike nearby stars, other galaxies are so far away that they appear stationary. Therefore, Hubble was forced to use indirect methods for measuring distances to other galaxies.
The apparent brightness of stars depends on two factors: actual luminosity and distance from Earth. For the closest stars, astronomers can measure the apparent brightness and distance, which allows them to calculate their luminosity. Knowing the luminosity of stars in other galaxies, you can calculate the distance to them by measuring their brightness.
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Some scientists hypothesize that our solar system, or even the galaxy, may be just an atom of some other giant universe. Such a world is shown in the final scene of the film "Men in Black": the Universe is just an atom of a ball in the hands of an alien creature.
In our Galaxy (according to modern estimates) there are 200 to 400 billion stars, about 50 billion planets, of which 500 million are potentially habitable. The mass of the Milky Way is estimated at 31,012 solar masses. Most of the mass of the Galaxy is contained not in stars and interstellar gas, but in dark matter, the weight of which is 10 times greater than all the stars combined.
According to Carl Sagan, up to a million civilizations can exist in our Galaxy. If intelligent life forms are evenly distributed throughout the Galaxy, then one of the inhabited planets can be expected to be found "nearby" - just a few hundred light years from the solar system.
The Milky Way belongs to a group of 40 galaxies located close to each other that have gravitational effects on each other. The closest galaxies to each other are the Milky Way and Andromeda, the distance between them is 2.5 million light years. The Andromeda Galaxy is twice the size of the Milky Way, with a diameter of 220,000 light years.
The Milky Way and Andromeda have been in gravitational interaction for millions of years, which ultimately will inevitably lead to the fact that the Andromeda galaxy will "pull" the Milky Way and the galaxies will "merge". The spiral arms of the Milky Way will be torn off, and our Sun, quite possibly, will be thrown into the void of space. Black holes at the centers of both galaxies will collide and "merge" together.
Astronomers claim that a galactic "confluence" may occur in 5 billion years. The calculations of scientists have shown that the gravitational attraction of Andromeda is stronger than the gravity of the Milky Way, as a result, our Galaxy flies towards Andromeda at a speed of about 120 kilometers per second!
The area accessible to astronomical observations is about 42 billion light years (the cosmic horizon), but the Universe is not limited to this area, since, as scientists believe, other universes, of which there are infinitely many, can extend further.
The famous astrophysicist of our time Stephen Hawking is convinced that our universe is not the only one. According to modern physical M-theory (membrane theory), there are many universes created from literally nothing, and their creation did not require the intervention of any supernatural being or God.
Albert Einstein said: “Man is a part of the whole, which we call the Universe, a part limited in time and space. He feels himself, his thoughts and feelings as something separate from the rest of the world, which is a kind of optical illusion. This illusion has become a prison for us. Our task is to free ourselves from this prison, expanding the sphere of our participation to every living being, to the whole world, in all its splendor."