The sun is the core of the solar system, about 150 million kilometers away from the earth, it is a massive star. It is the existence of the sun that leads to the birth of the solar system, the birth of life on earth and human beings. So, to some extent, the sun is also the mother of life on earth, the mother of human beings.
The sun is a big fireball that keeps glowing and heating. Only when the light and heat are transmitted to the earth can we have a beautiful ecosystem and the birth and evolution of life. So why does the sun glow and heat, and what is its combustion pattern like? Before human beings knew about nuclear fusion, many people thought that the burning of the sun was similar to the chemical burning on the earth.
But there is no oxygen in the universe, it is a vacuum environment, and chemical fuel can’t make the sun burn. It hasn’t been extinguished for 5 billion years. So this answer was denied by scientists. Until Einstein proposed the mass energy equation, we gradually realized two kinds of application modes of nuclear energy, and we knew the higher-level combustion mode of nuclear fusion.
The raw material needed for nuclear fusion is very simple, that is, the ubiquitous hydrogen in the universe, and the sun is a celestial body made of hydrogen. The huge pressure and internal temperature ignite the nuclear fusion in the center, making the sun a huge nuclear fusion reactor.
The light and heat emitted by the sun all the time is the radiation energy released to the surface after the nuclear fusion reaction in the center of the sun. So, as long as the nuclear fusion at the center of the sun is going on all the time, then the sun can burn all the time. Can the sun burn all the time? The answer is No.
Any combustion needs raw materials, and so does nuclear fusion, although its raw material is hydrogen, and the hydrogen contained in the sun is also very large. However, the sun is a celestial body with mass, and its hydrogen content is limited. When all the hydrogen is consumed, the nuclear fusion in the center will stop.
Without the transfer of fusion energy in the center, the sun will not go out, so there is a question: how long will it take for human beings to know after the solar fusion stops? Is it eight minutes? Maybe some friends think that the distance between the earth and the sun is 150 million kilometers, while the speed of photons is 300000 kilometers per second. Through calculation, it takes eight minutes for the light of the sun to reach the earth.
Therefore, many friends think that when the nuclear fusion of the sun stops, the earth will fall into darkness in eight minutes, and then we know that the sun has gone out. Is that really the case? If you think so, it’s a big mistake. The sun’s nuclear fusion, combustion and radiation energy transmission are far from as simple as we think.
Yes, nuclear fusion in the center of the sun will stop as long as the hydrogen is consumed. No new photons will be generated at this center, and the energy flow to the surface of the sun will be cut off. But have we ever thought about the time it takes for photons from nuclear fusion to reach the surface of the sun? Some people may say that the speed of photons is the speed of light. It’s not instantaneous when it reaches the surface of the sun?
If you think so simply, it’s wrong. The speed of light is 300000 kilometers per second, while the radius of the sun is 700000 kilometers. If the light quantum goes straight, it only takes two seconds to reach the surface from the center. Theoretically, this is true, but actually it is not. When light quantum moves from inside to outside, it will collide with countless atoms and electrons inside the sun.
The free path of the light quantum in the sun is about 1 cm, and the radius of the sun is 70 billion cm. In this way, the light quantum will have to make about 5 × 10 million turns like a drunk to reach the surface. Therefore, starting from the nuclear fusion at the center, the light quantum can’t walk in a straight line all the way. Instead, it has to go around many bends and take a long time to reach the surface. It takes as little as 5000 years and as much as tens of thousands of years.
A photon from the center of the sun to the surface takes at least the time that the whole human civilization has experienced. However, when it comes to the earth from the surface of the sun, there are no particles blocking it. It can arrive at the speed of light in a straight line, and it only takes eight minutes.
The complete extinction of the sun is very difficult to achieve in a short time. The process of the sun’s “death” is very complex and needs to go through several long stages. With the mass of the sun, its life span is about 10 billion years. Today’s sun has burned for 4.57 billion years. In another 5 billion years, the hydrogen of the sun will be consumed and hydrogen fusion will stop.
At this time, the sun began to evolve to “death”. Due to the depletion of hydrogen and the stop of hydrogen nuclear fusion, the pressure can no longer restrain the sun’s shell. At this time, the core shrinks, the shell will continue to expand, and the sun will turn into a red giant and become bigger and bigger.
A red giant is an unstable state at the end of a star’s life. Its diameter will continue to grow and devour the orbit around it. When the sun expands to become a red giant, its orbit will extend to the position of the earth. Mercury, Venus will be swallowed up, and then the earth. This process will last about 100000 years. As the sun expands, it will lose mass and the surface temperature will become lower and lower, eventually becoming a “white dwarf”.
So white dwarfs don’t glow? Of course not. Although the sun has evolved into a white dwarf after going through the red giant stage, it is still glowing and heating, but the brightness and temperature will drop sharply. White dwarf is actually the core of the sun after collapse. It is a very dense object. The white dwarf is not the final result. As time goes on, it will evolve to the final destination, the black dwarf. This is the final result of the sun. At that time, the sun will be completely extinguished.
However, the evolution process from the sun to black dwarfs is too long. At present, scientists have not found black dwarfs in the universe. There are two reasons for this. One is that it may take longer for a star to evolve into a black dwarf than the age of the universe. At present, no star in the universe has evolved into a black dwarf.
Another reason is that we can’t observe it. We need to know that black dwarfs don’t emit any radiation and energy. With the current observation technology of human beings, if there is no energy radiation, the telescope is blind and can’t see anything. Therefore, even if there are black dwarfs in the present universe, it is difficult to find them with the existing human observation technology, unless we have more powerful observation technology.
Thus, it can be seen that it will take a long time for the sun to go out completely, at least tens of billions of years or more. Whether human beings can continue to that time is still unknown. For human beings, even if the nuclear fusion inside the sun stops completely, it is very difficult for us to really find out. Only when the sun begins to expand and transform into a red giant, can we know that the nuclear fusion inside the sun has stopped.
So can humans wait on earth until the day when the sun becomes a red giant? I’m afraid it’s very difficult to know that before the sun evolves into a red giant, the surface temperature of the sun will become higher and higher, and the earth will become a fireball, and the surface temperature will become a purgatory world just like Venus.
If human beings want to survive, they have to leave the earth to live on other planets, such as Mars. And this time may be hundreds of millions of years later, far from the day when the sun becomes a red giant. Of course, if human science and technology were strong enough at that time, we still hope to build a closed ecological environment, continue to survive on the earth, and observe the evolution of the sun at a close distance.