Stars, like people, can be newborns, young, old. Every moment, some stars die and others form. Usually the youngest of them are similar to the Sun. They are at the formation stage and are actually protostars. Astronomers call them T type stars - Taurus, by the name of their prototype. By their properties - for example, luminosity - protostars are variable, since their existence has not yet entered a stable phase. Around many of them is a large amount of matter. Powerful wind currents come from type T stars.
Protostars: The Beginning of a Life Cycle
If a substance falls on the surface of a protostar, it quickly burns out and turns into heat. As a result, the temperature of protostars is constantly increasing. When it rises so much that nuclear reactions start in the center of the star, the protostar becomes ordinary. With the beginning of the course of nuclear reactions, the star has a constant source of energy, which supports its vital activity for a long time. How long the life cycle of a star in the Universe will be depends on its initial size. However, it is believed that stars with a diameter of the Sun have enough energy to exist comfortably for about 10 billion years. Despite this, it also happens that even more massive stars live only a few million years. This is due to the fact that they burn their fuel much faster.
Normal size stars
Each of the stars is a bunch of hot gas. In their depths, the process of generating nuclear energy is constantly happening. However, not all stars are like the sun. One of the main differences is color. Stars are not only yellow, but also bluish, reddish.
Brightness and luminosity
They differ in such signs as brilliance, brightness. The brightness of a star observed from the Earth’s surface depends not only on its luminosity, but also on its distance from our planet. Given the distance to the Earth, stars can have completely different brightness. This indicator ranges from one ten thousandth glint of the Sun to a brightness comparable to more than a million Suns.
Most of the stars are on the lower segment of this spectrum, being dim. In many ways, the Sun is an average, typical star. However, compared with others, it has a much greater brightness. A large number of dim stars can be observed even with the naked eye. The reason stars differ in brightness is because of their mass. Color, luster and brightness change over time is determined by the amount of substance.
Attempts to explain the life cycle of stars
Since ancient times, people have tried to trace the life of stars, but the first attempts of scientists were rather timid. The first achievement was the application of the Lane law to the Helmholtz-Kelvin hypothesis of gravitational compression. This brought a new understanding into astronomy: theoretically, the temperature of a star should increase (its index is inversely proportional to the radius of the star) until an increase in density slows down the compression processes. Then the energy consumption will be higher than its arrival. At this moment, the star will begin to cool rapidly.
Hypotheses about the life of stars
One of the original hypotheses about the life cycle of a star was proposed by astronomer Norman Lokier. He believed that stars arise from meteor matter. Moreover, the provisions of his hypothesis were based not only on the theoretical conclusions available in astronomy, but also on the data of spectral analysis of stars. Lokier was convinced that the chemical elements that take part in the evolution of celestial bodies consist of elementary particles - “proto-elements”. Unlike modern neutrons, protons and electrons, they have not a general, but an individual character. For example, according to Lokier, hydrogen decomposes into the so-called “protohydrogen”; iron becomes a proto-iron. Other astronomers also tried to describe the life cycle of the star, for example, James Hopwood, Jacob Zeldovich, Fred Hoyle.
Giant stars and dwarf stars
Large stars are the hottest and brightest. They are usually white or bluish in appearance. Despite the fact that they are gigantic in size, the fuel inside them burns out so quickly that they lose it in a few million years.
Small stars, as opposed to gigantic ones, are usually not so bright. They have a red color, they live long enough - for billions of years. But among the bright stars in the sky there are also red and orange. An example is the star Aldebaran - the so-called "bull’s eye" located in the constellation Taurus; as well as the star Antares in the constellation Scorpio. Why are these cold stars able to compete in brightness with red-hot stars, like Sirius?
This is due to the fact that once they expanded very much, and huge red stars (supergiants) began to exceed their diameter. The huge area allows these stars to radiate an order of magnitude more energy than the sun. And this despite the fact that their temperature is much lower. For example, the diameter of Betelgeuse, located in the constellation Orion, is several hundred times larger than the diameter of the Sun. And the diameter of ordinary red stars usually does not make up even a tenth of the size of the Sun. Such stars are called dwarfs. Each type of celestial body can go through these types of the life cycle of stars - the same star on different segments of its life can be a red giant or a dwarf.
As a rule, luminaries like the Sun maintain their existence due to the hydrogen inside. It turns into helium inside the nuclear core of a star. The sun has a huge amount of fuel, but even it is not infinite - over the past five billion years, half the reserve has been used up.
The life time of the stars. Star life cycle
After the hydrogen reserves are exhausted inside the star, serious changes come. Residues of hydrogen begin to burn not on the inside of its core, but on the surface. At the same time, the life time of the star is increasingly reduced. The cycle of stars, at least most of them, in this segment goes into the stage of the red giant. The size of the star becomes larger, and its temperature - on the contrary, less. This is how most red giants, as well as super giants, appear. This process is part of the overall sequence of changes occurring with the stars, which scientists called the evolution of stars. The life cycle of a star includes all its stages: ultimately, all stars age and die, and their duration is directly determined by the amount of fuel. Big stars end their lives with a huge, spectacular explosion. The more modest, on the contrary, die, gradually shrinking to the size of white dwarfs. Then they just fade away.
How long does the average star live? The life cycle of a star can last from less than 1.5 million years to 1 billion years or more. All this, as was said, depends on its composition and size. Stars like the Sun live between 10 and 16 billion years. Very bright stars, like Sirius, live relatively short-lived - only a few hundred million years. The star’s life cycle diagram includes the following steps. This is a molecular cloud - the gravitational collapse of the cloud - the birth of a supernova - the evolution of a protostar - the end of the protostellar phase. Then the stages follow: the beginning of the stage of a young star - the middle of life - maturity - the stage of the red giant - planetary nebula - the stage of the white dwarf. The last two phases are characteristic of small stars.
The nature of planetary nebulae
So, we examined briefly the life cycle of a star. But what is a planetary nebula? Transforming from a huge red giant into a white dwarf, sometimes the stars drop their outer layers, and then the star’s core becomes naked. The gas shell begins to glow under the action of the energy emitted by the star. This stage got its name due to the fact that luminous gas bubbles in this shell often look like disks around planets. But in reality they have nothing to do with planets. The life cycle of stars for children may not include all scientific details. You can only describe the main phases of the evolution of celestial bodies.
Star clusters
Astronomers are very fond of exploring clusters of stars. There is a hypothesis that all luminaries are born precisely in groups, and not individually. Since stars belonging to the same cluster have similar properties, the differences between them are true, and not due to the distance to the Earth. Whatever changes are accounted for by these stars, they start at the same time and under equal conditions. Especially a lot of knowledge can be obtained by studying the dependence of their properties on mass. After all, the age of stars in clusters and their remoteness from the Earth are approximately equal, therefore they differ only in this indicator. The clusters will be interesting not only to professional astronomers - every lover will be happy to take a beautiful photo, admire their exceptionally beautiful view of the planetarium.