The Universe encompasses everything that exists – matter, space, energy and time. Includes any star, planet or celestial body.
The huge expanse of the Universe is unthinkable for the human mind. The visible part of the universe stretches up to 1.6 square kilometers, and no one knows what is outside it.
Numerous theories have been elaborated about the birth and evolution of the Universe. The most accepted of these is the Big Bang theory, which assumes that the Universe was born in a huge explosion, about 15 billion years ago. This unique event gave birth not only to matter, but also to energy, space and even time. There is no point in talking about events or times before the big explosion: there was nothing “before” it.
The astronomers’ opinion is that after the huge explosion, the universe was unimaginably hot, and strong radiation occurred. After about 10 seconds, the component particles of the atoms – protons, neutrons and electrons – materialized. The atoms themselves – mainly hydrogen and helium – formed millions of years ago, when the temperature dropped and the mass of the universe increased enormously.
If the great explosion occurred 15 billion years ago, the Universe should have a temperature of about 3K, which is three degrees above absolute 0 – that’s exactly what astronomers think. The radio telescopes received a background radiation from any direction, corresponding to a temperature of 3K. This is supposed to be the delayed effect of the big explosion. In the Universe, all bodies have a power of attraction, called gravitational force. This force is a basic characteristic of each body, and is directly proportional to its mass.
Gravity is the force that keeps astronomical bodies in orbit. The moon is in orbit around the Earth instead of moving freely in space. The gravitational force of the Sun keeps the planets of the solar system in orbit, and the Sun in turn is held in a fixed position relative to other stars, with a much higher intensity force.
The sun is actually a regular medium-sized star. Like all stars, the Sun is a sphere of incandescent gases. This giant nuclear furnace emits a huge amount of light, heat and other energies. The sun, together with the planets around it, form the solar system. The rest of the stars seem very small compared to the Sun, but this is because they are much more distant. There are stars that are hundreds of times larger in diameter than the Sun.
Astronomers determine the position of stars according to constellations. The constellation is a group of stars, which can be seen at night in a certain area of the sky. They are not necessarily close to each other.
Galaxies – true star islands – represent groups of higher order stars. The solar system is part of the galaxy called the “Milky Way”. The Milky Way is by far not the largest galaxy, rather a medium one, yet its size is unimaginably large. In astronomy distances are measured based on the speed of light (300,000 km / s), which is the highest known speed. The unit of measurement used by astronomers is light-year, that is the distance traveled by light in a year. It is about 9.46 billion miles. The closest star is Proxima Centauri. Its distance from our solar system is 4.3 light years, meaning we see it as it was four years ago. Even sunlight needs eight minutes and twenty seconds to reach us.
The Milky Way looks like a huge wheel with a prominent hub. It contains hundreds of billions of stars. The sun is at its extremity, about 25,000 light-years from the center, and it needs about 250 million years to travel in full orbit once.
Galaxies are moving away from each other and at the same time, as if the Universe were expanding. This fact inspired the theory of the great explosion.
Stars can be of many types. Their occurrence and extinction are measured in millions of years. Our sun is about 5 billion years old, and according to astronomers, it is still longer to live until it begins to die. The sun is a single star, but there are double stars, made up of two stars that spin one around the other. There are also triple or multiple stars.
The biggest stars are called super-huge. For example, the diameter of the Antares is 330 times larger than the diameter of the Sun. Super-giants have very low densities. Following, in order of magnitude, huge stars, which are 10 or 100 times larger in diameter than the Sun. And these have low densities, but not like super-giants. Most of the visible stars are of medium category, as is the Sun. These are also called the main series stars. Their size can be ten times larger or smaller than that of the Sun.
The smallest stars in the main series are the red dwarfs. The white dwarfs, which represent the second category of small stars, are no longer part of the main series. They are the size of Earth and have very pale lights. Their density is extremely high – from 100,000 to 20 million times denser than water. Astronomers believe that their number can reach 5 million in the Milky Way alone. So far only a few hundred have been identified.
Each star begins life as a cloud of dust and hydrogen. There are a very large number of such clouds in the Universe. The formation of a star begins when, for some reason (it is not known exactly which), this cloud begins to contract due to gravity. As the cloud contracts, it begins to spin and its center heats up. When the temperature of the central core is sufficiently heated – we are talking about the order of millions of degrees – nuclear reactions take place.
The new star is surrounded by remains of gas and dust. In the case of the Sun, the planets formed from these remnants. It is almost certain that other planets have formed around other stars, on which there may be some form of life. This in itself is an extraordinary possibility.
The fate of a star depends largely on its mass. If it were known that the Sun consumes its “fuel” of hydrogen, the helium nucleus shrinks and the outer layers expand. In this state, the stars are called huge reds. The outer layers disappear with time, and only the small white nucleus remains – this is the white dwarf. The star gradually cools, eventually becoming a black dwarf – a large piece of carbon.
Stars that have a mass far above the Sun’s mass end more dramatically. As their nuclear fuel runs out, they become super-huge in volume much larger than that of the red giants. Then, under the effect of gravity, the collapse of the nucleus takes place, and the released energy fragments the star through a huge explosion. This is the supernova state. Supernovae shine a billion times more powerful than the Sun. In February 1987, a supernova from a neighboring galaxy was visible and without a telescope. A similar phenomenon had not been seen for 383 years. After the supernova state, depending on the initial mass, there remains a small celestial body, called “neutron star”. Its diameter is tens of kilometers, and is composed of a compact neutron mass. The density of these stars far exceeds that of the white dwarfs.
Sometimes the nucleus of supernovae collapses with such force that the matter disappears completely. What remains is just a space with huge gravity. Her power is so great that nothing can escape her, not even the rays of light. These spaces are called Black Holes.
Because of their nature, black holes are not visible, but astronomers believe they have managed to locate a few specimens. We are looking for double or multiple stars with strong X-ray emissions. It is assumed that matter flows from the star into the black hole on a spiral orbit. The phenomenon was detected for example in the constellation Cygnus X-1. Some scientists also believe in the existence of “white” gaps and they think that these are places where matter comes out to start a new life.
In the Universe there are other mysterious celestial bodies, for example the marriages. These appear to be very bright centers of some galaxies. Some of them are the most distant objects in the Universe. Their light started toward us shortly after the birth of the world. It is believed that the energy emitted by the ambassadors could only come from the black holes.
The pulsars are just as fascinating. They periodically emit energy pulses at regular intervals. These are assumed to be fast revolutionary neutron stars. Nobody knows what the final fate of the Universe will be. According to the theory of the open universe, the expansion will continue until all the stars die and all the energy is scattered in space. The closed universe theory assumes that at one point the universe will begin to contract and eventually disappear in an event called Big Crunch, the opposite of Big Bang. This state can cause a new explosion, which could create a new Universe, and thus an infinite number of explosions and contractions can be generated – an oscillating Universe.