On the first day of the new year, "The Wandering Earth 2" is about to be released. Let's briefly review the plot of the first installment, and its scientific setting: something went wrong with the sun.
In "The Wandering Earth 1", astronomers confirm that the sun begins to expand, the earth continues to heat up, and in 100 years, the sun will engulf the earth's orbit, and the countdown to the survival of human civilization begins. People around the world have come together like never before, creating planetary engines that drive Earth to Proxima Centauri.
Leave the movie, stand on the ground, stomp your foot ... Nothing will happen.
The total mass of the entire earth is close to 6000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000 The earth uses such a large mass to counter its own strong gravity, so that when the earth bears its own gravity, it will not collapse at will, nor will it shrink into a ball.
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The sun, whose total mass is hundreds of thousands of times that of the earth, has not been able to squeeze the sun because it is supported by another force - the radiant pressure of light.
The gravitational pull of the sun points to the core, and the radiation of the released light points outward, and the two forces balance each other, so that we have a stable glowing sun. A stable sun means to us the environment in which we live, and it means everything we are used to today.
However, the sun is not always so stable.
The newborn sun is relatively tyrannical, the core mechanism for manufacturing nuclear fusion reactions is not yet mature, and the outside is shrouded in a dense molecular cloud, and the entire sun is like an adolescent child, cloudy and unstable. The aging sun has lost its original energy source and relies on alternative mechanisms to output radiation, which is becoming more and more abnormal.
Only the sun in the prime of today's life is rich and strong.
Deep in the core of the sun, nuclear fusion is constantly going on. In a high-temperature and high-pressure environment, atomic nuclei are forced to squeeze together, and the instinctive repulsion between atoms and atoms is difficult to resist the force that squeezes them, and eventually, the nuclei are rearranged, and protons and neutrons recombine into helium atoms. Such a process is accompanied by the release of enormous energy. The energy released comes to the earth, which is the sunlight we see. This is the most efficient "engine" in the universe, energy is continuously produced, new atoms are synthesized and stored in the core of the sun, but for the entire sun, the loss of volume and mass is negligible.
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The sun has existed as an "atomic machine" for nearly 4.5 billion years, and this will continue for another 4.5 billion years in the future. But once the hydrogen atoms in the sun's core are depleted and the stock of materials to synthesize new atoms is low, everything will end.
5 billion years later, when the hydrogen in the core of the sun is basically converted into helium, can no longer produce energy to radiate outward, and the inward gravity begins to dominate everything, the core of the sun will collapse inward, the internal temperature will rise, and a stronger reaction ignites the rest of the hydrogen outside the core, and the outer material pushes outward, and the entire sun increases by two to three times, becoming a "subgiant".
Subsequently, the entire sun continued to expand outward, the efficiency of generating energy was greatly reduced, the yellow-white light of the past was no longer there, replaced by only orange-red dark light, and the sun entered the final stage of life in a large and red posture. At this time, the solar core continues to fall and contract, and the core temperature continues to rise, igniting helium, a product of the past reaction, so that helium begins a new nuclear reaction to release energy. During this reaction, a brief helium explosion occurs called a "helium flash". As helium burns dramatically, the outer layer of the sun continues to expand, becoming a "red giant". Aldebaran in Taurus and Arcturus in the constellation Shepherd are approaching such a stage.
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The process of the expansion of the sun makes the originally yellow-white light of the prime appear red, turning the sun into a huge red giant. The red giant's color means that its surface temperature is several thousand degrees cooler than in the past. But because of the expanded size, the brightness of the red giant increases dramatically, equivalent to 10,000 times the brightness of the Sun during the stabilization phase. At the same time, the sharp approach of the Earth to the surface of the Sun makes us feel a sharp increase in temperature.
In this process, the sun's violent radiation blows away a large amount of the outer mass, and the gravitational pull of the sun, which has lost its mass, naturally reduces on the earth. As a result, Earth and the Sun will become farther apart and will orbit the Sun in a larger orbit, almost close to the orbit of Mars today. But eventually the inflated sun can engulf Mercury, Venus, and Earth in the innermost layers of the solar system, and the red edge of the sun is close to the orbit of Mars.
This is not the imagination of "The Wandering Earth", this is a real fate. The radius of the sun expands 250 times, which is equivalent to turning a watermelon into a movie theater in a very short time. The roaring solar wind swept the world, turning the earth into scorched earth and then falling in a huge solar fireball.
The Sun that turns into a red giant turns Earth into purgatory. Image credit: Wikimedia Commons
The completely burned sun throws out its shell, leaving only a dense core that gradually cools like a piece of burnt charcoal, which is the white dwarf. White dwarfs have only half the mass of the original Sun. The shell thrown out is dust and gas, which are blown into space and diffuse, becoming a large cloud-like existence, which is the planetary nebula. In this way, the sun returned the new atoms it made to the universe through dust and gas. Dust and gases rich in new atoms slowly float, diffuse, cool, dead - the cemetery of the solar system.
Over the course of each day, hundreds of millions of stars are being born across the entire observable universe, and hundreds of millions are coming to the end of life. Catastrophe for the earth and life on it is just the norm in the universe. The sun mentioned in "The Wandering Earth" entered the aging stage in advance and will expand into a red giant within the next 100 years. Thanks to the sun and its gravitational laws, none of this has happened yet.
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Author: Gao Shuang Popular science writer, Ph.D. in astronomy from Heidelberg University
Reviewed: Liu Qian is a researcher at the Beijing Planetarium