Why can't the sun always burn out? When it comes to the end, will it run out of fuel?

The sun keeps burning and burning, emitting enormous light and heat, which consumes a lot of fuel. But the sun has been burning for 5 billion years, why can't it burn all the time? It is said that the sun will die in 5 billion years. Is the sun running out of fuel by then? Many friends have this kind of question. Today, I will discuss this topic in a popular way, hoping to help my friends clear their doubts.

Doomsday.

Scientists have already made fortunes for the sun. The lifespan of a yellow dwarf like the sun is about 10 billion years. Now the sun is 4.6 billion years old, and it has a lifespan of about 5 billion years. A yellow dwarf star with the mass of the sun will return to light before it dies, expanding into a huge red giant star with a radius of about 200 to 300 times the original size. At that time, it will be the end of the sun.

The surface temperature of the red giant is still about 3000K. In the process of expansion, Mercury and Venus cannot escape doom, and it seems to be a foregone conclusion that they are swallowed up by the sun. Whether the earth will be swallowed up, there are many theories. If the red giant star expands 200 times, the radius of the sun is now about 700,000 kilometers, 200 times is 140 million kilometers, and the earth is 150 million kilometers away from the sun, and then there is still a distance of 10 million kilometers. It may not be swallowed, but Will be baked into a baked potato.

But it is impossible for the sun red giant to expand the radius by 200 times, and if it is more than 200 times, the earth will of course be swallowed up.

It is also believed that in the late stage of the sun's evolution, the outer layer will continue to release gas, and finally the mass of the sun will be reduced to 60% of its current size. In this way, the earth floats to a place 255 million kilometers away from the sun, and the sun's red giant star expands more than 300 times its current diameter to swallow the earth.

The end and direction of the solar system.

The mass of the sun occupies 99.86% of the solar system. All the planets revolve under the gravitational pull of the sun. Once the sun dies, will the descendants of the sun still exist?

One theory is that if the earth is not swallowed, then Mars, Jupiter, Saturn, Uranus, Neptune will be left, but it is almost dead. Because the gas surrounding the sun's red giant will gradually drift into the air, and eventually only a dense carbon core will be left. This carbon core is about the same size as the current Earth, but has more than 50% of the mass of the current sun, so its density reaches 1 ton/cm^3 or more.

This is the corpse of the sun ~ a white dwarf. The gravitational force of white dwarfs is much smaller, and the light and heat are already very weak, and the remaining planets are almost immersed in the darkness, and will become extremely cold, with temperatures close to absolute zero; and white dwarfs whose gravitational force has been much smaller, can contain Live on a planet that has escaped? If not, these planets will drift farther and farther, and eventually disappear into the dark and cold space and become stray planets.

There is also a saying that Jupiter has an opportunity at this time. The largest planet in the solar system may "eat up" the material scattered by the sun into space, and grow itself through accretion. When its mass reaches 8% of the sun's, it can stimulate nuclear fusion in its core and become the smallest star ~Red dwarf. And Mars, Earth, etc., which are close to Jupiter, may switch to new masters and revolve around this "self-reliant king" nova.

In this way, the solar system becomes a binary star system with a red dwarf star and a white dwarf star, and a new star system is formed. I have analyzed and discussed this issue many times in the past. Interested friends can refer to my past articles, and I will not go into details here.

lifespan of stars.

We know that all stars are mainly composed of hydrogen and helium elements. If calculated by volume, hydrogen accounts for about 90%, helium accounts for less than 10%, and the remaining elements are about 1%. And all stars form centripetal gravitational pressure because of the huge mass, which puts the core part under high temperature and high pressure, which triggers hydrogen nuclear fusion. The nuclear fusion of the core produces a huge radiation pressure, which withstands the centripetal gravitational pressure of the huge mass of the star and forms a balance. This is the main sequence star stage of the star, that is, the main sequence star with the most stable life cycle and the longest life cycle. stage. We usually say that the sun has a lifespan of 10 billion years, which is the lifespan of its main sequence stars.

The continuous nuclear fusion in the center of the star produces huge energy radiation, which makes the star stably emit light and heat in the main sequence star stage, and continuously radiate energy into space. So how big is this energy consumption? How long does it take for a star to burn through its fuel?

Different stars have different degrees of nuclear fusion, so the rate of fuel consumption is also different. The basic common sense is that the more massive the star, the higher the core gravitational pressure and temperature, the more intense the nuclear fusion, the faster the fuel burning, and the shorter the lifespan; and the smaller the star, the higher the central gravitational pressure and temperature. Low, the fusion will be gentler, the fuel consumption will be less, and the life will be longer.

So far, the most massive star discovered by humans is the blue supergiant star r136a1, which is more than 200 times the mass of the sun and has a lifespan of only more than 3 million years; while the smallest star, the red dwarf, has only 8% of the mass of the sun and has a lifespan of 100,000 years. Hundreds of millions of years, basically how long the universe has lived, how long it will live.

How much energy is produced by nuclear fusion in the sun?

Yellow dwarfs such as the sun account for about 10% of the universe and belong to small and medium-mass stars with a lifespan of about 10 billion years. Scientific research believes that a star with the mass of the sun has a core temperature of about 15 million K and a pressure of 300 billion Earth's sea-level atmospheric pressure.

Under such huge pressure and temperature, the fusion of 4 hydrogen nuclei into one helium nucleus has been taking place in the core, and 600 million tons of hydrogen are converted into 595.8 million tons of helium every second, which produces about 0.7%, That is 4.2 million tons of quality loss. Where have these qualities gone? It is converted into energy, and in the form of electromagnetic radiation, it reaches the surface of the sun from the core through the radiative layer and the troposphere, and then radiates into space.

How big is this energy? Einstein's mass-energy equation gave the answer. The expression of the mass-energy equation is: E=MC^2, where E is energy, M is mass, and C is the speed of light. The mass-energy equation reveals the equivalence exchange relationship between mass and energy, which is a great leap in human understanding of matter and energy.

According to the mass-energy equation, it can be calculated that the sun can produce 3.78*10^26J (joules) of energy per second. How much energy is this? The equivalent of one ton of TNT high explosive explosion is 4180000000J, and the energy released by the sun per second is equivalent to the energy of 900 million tons of explosives exploding at the same time. The total yield of nuclear bombs in the world is less than 10 billion tons, which means that the energy released by the sun in one second is equivalent to 9 million times that of all the nuclear bombs on the earth.

Does the sun run out of fuel when the sun is dying?

Simply put, not at all. The sun burns for 10 billion years, far from burning out its own hydrogen fuel. We are now based on the sun's lifespan of 10 billion years and a simple calculation based on the current burning rate given by scientists.

The sun converts 4.2 million tons of mass into energy every second, which is a loss of 4.2 million tons of mass. 1 astronomical year (Julian year) is 31557600 seconds, and it consumes about 1.3*10^27kg in 10 billion years, which only accounts for about 0.00066 of the total mass of the sun, which is less than 7/10,000; if the sun is 600 million per second If a ton of hydrogen is converted into helium, then the consumption of hydrogen in 10 billion years is about 1.9*10^29kg, which only accounts for about 10% of the total mass of the sun.

Therefore, it can be seen that when the sun dies, its fuel is still sufficient, so its death is not caused by burning out hydrogen, but a mutation in the overall evolution mechanism.

This is because the fuel involved in nuclear fusion in the sun is mainly concentrated in an area with a radius of 0.25 of its core. When the fuel in this area is almost burned, the nuclear fusion will be extinguished. Without the enormous tension of the radiation to resist the gravitational pressure, the stellar matter would collapse towards the core, resulting in higher temperatures and pressures that would trigger the fusion of the helium nuclei that have been fused and accumulated in the core.

After the fusion of helium ends, it collapses again, leading to a series of subsequent nuclear fusions, eventually ending with carbon. The core of a star with the mass of the sun does not have the pressure and temperature to initiate carbon nuclear fusion, so the sun has come to the end of its life, leaving a dense carbon core remains.

Stellar evolution is roughly the same, but the results are different for different masses.

Stars with more mass than the sun can fuse all the way, and only stars with more than 8 times the mass of the sun can fuse to the end of the iron core. Because the iron core is the most stable element, neither nuclear fission nor nuclear fusion can produce energy, but consumes energy, which cannot be provided by any star in the later stages of evolution, so the final core fusion of any star ends with iron. .

However, the collapse and compression of massive stars much more violently than the sun will cause the core thermonucleus to run out of control, thus causing a supernova explosion. After the smoke is exhausted, a neutron star or black hole will be left in the core according to the size of the mass. It is generally believed that a star with more than 8 times the mass of the sun will leave a neutron star in its core after the big bang, which is 1.44 times larger than the mass of the sun and less than about 3 times the mass of the sun; stars with a mass of 30 to 40 times more than the sun will leave a neutron star in the core after the big bang. The next black hole with more than 3 times the mass of the sun.

After all stellar evolutions complete a life cycle, they do not consume much hydrogen fuel. The excess hydrogen and helium are returned to space in various ways, and these small residual substances will form new molecular clouds, brewing. A star formation. This is why the universe has undergone 13.8 billion years of evolution, and the hydrogen and helium elements still occupy the absolute abundance, and the rest of the elements add up to only about 1%.

And these 1% or so heavy elements are obtained from the evolution of celestial bodies such as stellar nuclear fusion, supernova explosions, and neutron star collisions. Without these, life and civilization would not be born.

That's all for today, thank you for reading, and welcome to discuss. It's not easy to code words. If you like my article, please give it a like and follow, thank you.