A star is a celestial body that radiates light. It differs from planets, comets, satellites, and nebulae that are illuminated in the sky by the sun or nearby stars.
The substance that makes up the stars in the sky is hot gas - plasma.
The highest temperature on the surface of this massive gas ball reaches one hundred and fifty thousand degrees. (This is the surface of a white dwarf that has formed.)
How do astronomers get to know these celestial objects?
With the help of observations, astronomers first of all determine the mass, radius, and temperature on the surface. Although we do not see the depths of the stars, we know that they consist of plasma.
Temperature is measured by analyzing the radiation coming from the surface of this celestial body. No photon can escape from the depths of stars, so we never get to know the "insides" directly.
And yet a man is able to accurately calculate the temperature at any point in the depths of this cosmic body. So, for example, in the center of the Sun temperature reaches thirteen million. More than three billion people reach the temperature in the depths of the stars with the highest mass.
Composition
Stars in the sky are huge yet simple particle systems.
A medium-sized space balloon of gas is made up of an incredibly large number of nucleons (protons and neutrons), which can be expressed in a number with fifty to seven zeros.
A number of nucleons of our Sun in three hundred thousand times exceed the number of nucleons from which the Earth consists. The quantity of the substance in this body and weight expresses quantity of nucleons from which it develops.
Despite the fact that the Sun as a system of sizes is many times larger than the Earth, yet it is much simpler than our planet in composition. This is the chemical composition of the Sun that ensures the evolution of mankind.
The Earth, like other planetary bodies, consists of rocks, rocks - of crystals, crystals - of molecules, molecules - of atoms, atoms - of nuclei and electrons.
Stars in the sky are made of nuclei and electrons only. It is because of its simple composition that it is easy to determine the temperature, mass, pressure and chemical elements at any point within. But we are not yet able to calculate the same characteristics of the Earth.
It is worth noting the fact that astronomers know the depths of distant stars better than the depths of the planet on which we live.
The properties and behavior of plasma are now quite well studied: for example, it is known that the pressure in plasma is the higher the hotter and denser it is. At the same time, the pressure at a certain point inside is equal to the weight of all layers above this point.
If the plasma pressure rises, the star expands, otherwise, it shrinks.
Even the smallest ones have a mass about ten thousand times the mass of the Earth.
The largest stars in the sky are millions of times the mass of the Earth.
Dimensions
The size of the stars in the sky can be very different.
White dwarfs are equal in size to the Earth, while their density is about a million times the density of the earth.
The smallest stars that have been observed are neutrons. They are one hundred million times smaller than the Earth in volume. In order for such a small volume could fit a huge mass, not inferior to the mass of conventional neutrons must have a fantastic density. The substance of these objects consists only of neutrons. They are observed as pulsating sources of radio emission and are called pulsars.
Neutron stars in the sky - pulsars have a mass several times greater than the mass of the Sun.
Evolution of development
The evolution of a star is a gradual increase in temperature in its depths.
Evolution begins with a dark gas-dust nebula, whose temperature rises and can eventually reach the core of iron, with a temperature of three and a half billion. Then gravity begins to compress the globule into a protostar as the final stage of formation.
Mass
If the mass of the star is less than 0.08 MQ (MQ is the mass of the Sun), the temperature in its depths does not reach the level required for hydrogen combustion. For example, a celestial object with a mass of 0.06 MQ is heated by gravity to a temperature of only 2.5 million degrees, which is not enough to turn hydrogen into helium. Such a gas ball can only live off the forces of gravity. The spectrum of its radiation is predominantly infrared. When the force of gravity stops compressing the star (becomes completely degraded matter), it loses its energy source. As a result, the ball cools down and turns into a black dwarf.
If the mass ranges from 0.08 MQ to 4.0 MQ, the nebula becomes a light star. Our Sun also belongs to the group of light stars of yellow dwarfs. Temperatures in the bowels can reach several hundred million degrees. This means that all thermonuclear reactions do not occur in them.
Heavier stars in the group (1.4 MQ to 4.0 MQ) are called the red giant. During the course of their lives and especially in old age, they get rid of most of their plasma, throwing it into the interstellar space. The result of the last release of plasma is a planetary nebula.
The red giant consists of a massive degenerated core of the Earth's diameter and a huge, rare plasma shell of the convective zone.
A globule or gas dust nebula with delineated boundaries and a high density of 4.0 MQ-8.0 MQ, evolves into a massive star whose core is heated to over three billion degrees Celsius.
Thus, the stars in the sky represent celestial luminaries with different "extraterrestrial" characteristics and properties.