The evolution of stars is a red giant

The red giant, as well as the supergiant is the name of space objects with extended shells and high luminosity. They belong to the late spectral classes K and M. Their radii exceed the solar radii by hundreds of times. The maximum radiation of these stars falls on the infrared and red regions of the spectrum. On the Hertzsprung-Russell diagram, the red giants are located above the main sequence line, their absolute magnitude varies within a little above zero or has a negative value.

The area of such a star exceeds the area of the Sun by a minimum of 1500 times, while its diameter is approximately 40 times larger. Since the difference in absolute value with our luminary is about five, it turns out that the red giant emits a hundred times more light. But it is much colder. The solar temperature is twice as high as the red giant, and therefore per unit surface area, the luminary of our system emits light sixteen times larger.

The visible color of the star depends directly on the surface temperature. Our Sun is white-hot and has a relatively small size, so it is called a yellow dwarf. The colder stars have orange and red light. Each star in the course of its evolution can reach the last spectral classes and become a red giant in two stages of development. This occurs in the process of nucleation at the stage of star formation or at the final stage of evolution. At this time, the red giant begins to radiate energy at the expense of its own gravitational energy, which is released when it is compressed.

As the star contracts, its temperature increases. At the same time, due to the reduction in the dimensions of the surface, the luminosity of the star decreases at times. It fades. If it is a "young" red giant, then ultimately, a thermonuclear fusion reaction from helium hydrogen will start in its bowels. After that the young star will be released on the main sequence. Old stars have a different fate. In the late stages of evolution, hydrogen in the bowels of the sun burns completely. Then the star descends from the main sequence. According to the Hertzsprung-Russell diagram, she moves to the region of supergiants and red giants. But before moving to this stage, it passes through an intermediate stage - the sub-gigant.

Subgigants are stars whose nuclei have already stopped hydrogen fusion reactions, but helium burning has not yet begun. This is because the core is not warmed up enough. An example of such a subgiant can be Arthur, located in the constellation Bootes. He is an orange Veda with an apparent magnitude of -0.1. It is located at a distance from the Sun about 36 - 38 light years. You can observe it in the Northern Hemisphere in May, if you look directly to the south. The diameter of Arthur is 40 times that of the sun.

Yellow dwarf The sun is a relatively young star. Its age is estimated at 4.57 billion years. On the main sequence, it will remain about 5 billion years. But scientists managed to model a world in which the Sun is a red giant. Its dimensions will grow 200 times and reach the Earth's orbit, incinerating Mercury and Venus. Of course, life will be impossible by this time. At this stage, the Sun will exist approximately another 100 million years, after which it will turn into a planetary nebula and become a white dwarf.