What is a red giant? The so-called red giant star, as its name implies, is a huge star with a red appearance (emitting red light). Red giant is a kind of luminous giant with huge volume and small mass, which evolved at the end of the star's life. The mass of red giant stars is usually around 0.3~8 suns, but due to the thin expansion of the external atmosphere, the volume of red giant stars is often dozens or even hundreds of times that of the sun. The surface temperature of the red giant is about 5000K(K is Kelvin temperature, about 4700 degrees Celsius) or lower.
When the star consumes all the hydrogen fuel in the inner core, the thermonuclear reaction will not continue, then the inner core of the star will begin to shrink inward due to gravity and the combustion will transfer to the outer hydrogen layer. At this time, the outer layer of the star will continue to expand, the heat generated by combustion will spread into space, and the surface temperature will begin to decrease. At the same time, the visible light output of the star will gradually move to red, and the life stage of the red giant star will begin.
When a star is in the main sequence stage, a nuclear fusion reaction will occur inside, consuming its own hydrogen fuel. The outward expansion force generated by the reaction is balanced with the inward collapse gravity, so that the star remains stable. The closest star to our earth, the sun, has a thermonuclear fusion reaction, and about 600 million tons of hydrogen will become helium every second. When all the hydrogen in the star becomes helium, the nuclear fusion reaction rate inside the star drops sharply, and the inner core of the star will collapse inward due to gravity, thus forming white dwarfs, neutron stars or black holes. The exterior of the star will continue to burn.
The external combustion of a star and the internal thermonuclear fusion reaction can be very different, especially the degree of reaction, which can be said to be quite intense. This makes the star have to adjust its star structure accordingly to adapt to this reaction. After about 654.38+0 billion years, the energy outflow from the star core gradually stabilized. In the next few hundred million years, the star will temporarily enter a stable state, the helium in the inner core will continue to be consumed, the hydrogen will continue to burn outward, and the outer gas shell of the star will expand more and more to adapt to its own structure. At this time, the volume of the star can be increased to 65.438+0 billion times at most, and the bright color in the process will gradually turn red.
However, when there is not enough mass inside the red giant, the carbon and oxygen will be further merged, and these two elements will form a core inside the star, which is a white dwarf. At this time, the expanding gas shell of the red giant star will gradually break away from the gravitational bondage of the inner core and spread into space to form a nebula-of course, if the mass of the inner core of the star is large enough to further fuse carbon and oxygen into iron, then the inner core of the star will also become a neutron star or even a black hole.
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