Stars, like people, can be newborn, young, old. Every moment some stars die and others are formed. Usually the youngest of them are similar to the Sun. They are at the stage of formation and actually represent protostars. Astronomers call them T-Taurus stars, after 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 emanate from T-type stars.
Protostars: the beginning of the life cycle
If matter 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 are triggered in the center of the star, the protostar acquires the status of an ordinary one. With the onset of nuclear reactions, a star has a constant source of energy that 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. HoweverIt 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.
Regular sized stars
Each of the stars is a bunch of hot gas. In their depths, the process of generating nuclear energy is constantly going on. However, not all stars are like the Sun. One of the main differences is in color. Stars are not only yellow, but also bluish, reddish.
Brightness and luminosity
They also differ in such features as brilliance and brightness. How bright a star observed from the surface of the Earth will be depends not only on its luminosity, but also on the distance from our planet. Given the distance to the Earth, the stars can have completely different brightness. This figure ranges from one ten-thousandth of the brilliance of the Sun to a brightness comparable to more than a million Suns.
Most of the stars are at the lower end of this spectrum, being dim. In many ways, the Sun is an average, typical star. However, compared to 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 change in brightness over time is determined by the quantitysubstances.
Attempts to explain the life cycle of stars
People have long tried to trace the life of the stars, but the first attempts of scientists were rather timid. The first advance was the application of Lane's law to the Helmholtz-Kelvin hypothesis of gravitational contraction. This brought a new understanding to astronomy: theoretically, the temperature of a star should increase (its value is inversely proportional to the radius of the star) until the increase in density slows down the contraction processes. Then the energy consumption will be higher than its income. At this point, the star will begin to rapidly cool.
Hypotheses about the life of stars
One of the original hypotheses about the life cycle of a star was proposed by astronomer Norman Lockyer. He believed that stars arise from meteoric matter. At the same time, the provisions of his hypothesis were based not only on the theoretical conclusions available in astronomy, but also on the data of the spectral analysis of stars. Lockyer was convinced that the chemical elements that take part in the evolution of celestial bodies are composed of elementary particles - "protoelements". Unlike modern neutrons, protons and electrons, they have not a general, but an individual character. For example, according to Lockyer, hydrogen breaks down into what is called "protohydrogen"; iron becomes "proto-iron". Other astronomers also tried to describe the life cycle of a star, for example, James Hopwood, Yakov Zeldovich, Fred Hoyle.
Giant and dwarf stars
The big stars are the hottest and brightest. They are usually white or bluish in appearance. Although they are gigantic in size, the fuel inside them burns out so quickly that they are depleted of it in a mere few million years.
Small stars, as opposed to giant ones, are usually not as bright. They have a red color, live long enough - for billions of years. But among the brightest stars in the sky there are also red and orange ones. 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 cool stars able to compete in brightness with hot stars like Sirius?
This is due to the fact that once they expanded very much, and their diameter began to exceed the huge red stars (supergiants). 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 is usually not even a tenth of the size of the Sun. Such stars are called dwarfs. Each celestial body can go through these types of the life cycle of stars - the same star at different segments of its life can be both a red giant and a dwarf.
As a rule, luminaries like the Sunsustain their existence due to the hydrogen inside. It turns into helium inside the nuclear core of the star. The sun has a huge amount of fuel, but even it is not infinite - half of the reserve has been used up over the past five billion years.
Lifetime of stars. Life cycle of stars
After the supply of hydrogen inside a star is depleted, serious changes come. The remaining hydrogen begins to burn not inside its core, but on the surface. In this case, the lifetime of the star is decreasing more and more. The cycle of stars, at least most of them, in this segment passes into the stage of a red giant. The size of the star becomes larger, and its temperature, on the contrary, decreases. This is how most red giants, as well as supergiants, appear. This process is part of the overall sequence of changes that occur with the stars, which scientists called the evolution of stars. The life cycle of a star includes all its stages: in the end, all stars grow old and die, and the duration of their existence is directly determined by the amount of fuel. Large stars end their lives with a huge, spectacular explosion. More modest ones, on the contrary, die, gradually shrinking to the size of white dwarfs. Then they just fade away.
How long does an 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 starslike Sirius, live for a relatively short time - only a few hundred million years. The life cycle diagram of a star includes the following stages. 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 a red giant - a planetary nebula - the stage of a white dwarf. The last two phases are characteristic of small stars.
Nature of planetary nebulae
So, we briefly reviewed the life cycle of a star. But what is a planetary nebula? Stars sometimes shed their outer layers as they go from being a huge red giant to a white dwarf, leaving the star's core exposed. The gas envelope begins to glow under the influence of energy emitted by the star. This stage got its name due to the fact that the luminous gas bubbles in this shell often look like disks around planets. But in fact, they have nothing to do with the planets. The life cycle of stars for children may not include all the scientific details. One can only describe the main phases of the evolution of celestial bodies.
Star clusters
Astronomers love to explore star clusters. There is a hypothesis that all luminaries are born precisely in groups, and not one by one. Since the stars belonging to the same cluster have similar properties, the differences between them are true, and not due to the distance to the Earth. What kind of changesdid not fall to the share of these stars, they take their beginning 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 distance from the Earth are approximately equal, so they differ only in this indicator. The clusters will be of interest not only to professional astronomers - every amateur will be happy to take a beautiful photo, admire their exceptionally beautiful view in the planetarium.
