Shulou(Shulou.com)11/24 Report--

This article comes from the official account of Wechat: Earth knowledge Bureau (ID:diqiuzhishiju), author: forget the year

The original title: "scared to death, false alarm."

Author: forget the year

Proofread manuscript: Chao Qian / Editor: moth

On the first day of the Lunar New year, "wandering Earth 2" came back strongly. The sun is facing the crisis of destruction because of the "helium flash". Human beings have to build planetary engines to take the earth away from the sun's gravity and find a new home.

After watching the movie, some people may be worried that the sun will suddenly "helium flash". In fact, "helium flash" is a phenomenon when stars enter menopause, and our sun is still in its prime and will not be "helium flash" for at least 5 billion years. We don't have to worry too much. We should eat and drink.

This wandering journey will last for 2500 years.

(photo: stills of wandering the Earth) ▼

Why does the sun "helium flash"? Will it really destroy the earth? The answer lies in the evolutionary history of the sun.

When we look back at the magnificent life history of stars, we will find that the whole life of stars is a history of struggle constantly trying to break free from the control of gravity.

Hundreds of thousands of stars scattered throughout the Milky way

Feel this indescribable chaos (figure: NASA) ▼

Origin: the birth of a star 13.8 billion years ago, the time and space in which we live was created in a Big Bang. Within about 3 minutes after the Big Bang, the elementary particles produced from vacuum quantum fluctuations combine into protons and neutrons, and further synthesize about 75% hydrogen, 25% helium and a very small amount of lithium and beryllium.

The early universe was such a dark sea of chaos made up of large amounts of hydrogen and a small amount of helium until the first generation of stars emerged from it and emitted the first ray of light. Among them, gravitation is the most important cause of this process.

The Progress of the Universe (Picture: NASA) ▼

The sea of chaos in the universe is not absolutely uniform and dead, under the action of gravity, small disturbances are slowly magnified, sparse places become more and more sparse, dense places become denser and denser, gradually forming primitive "matter clouds".

According to the Jenkins gravitational instability theory, clouds that meet certain conditions will continue to gather towards the center and then quickly collapse to form "protostars".

Star formation region of Carina Nebula NGC 3324

Stars are born in the "sea of the universe" filled with gas and dust.

(horizontal screen, picture: NASA's JWST) ▼

The collapse caused by gravity will not continue forever. Clouds compressed to a certain extent by gravity are increasingly trying to compete with their own pressure, but still have to contract slowly. But by this time, the interior of the protostar has become opaque, and more powerful energy is quietly brewing in the core.

Protostars in nebula L1527 (centered pink)

And the surrounding dust structure (figure: Wiki) ▼

Let's take a look at the Eagle Nebula M16, which is magnificent (photo: Wiki) ▼

The gravitational potential energy released by the protostar during the slow contraction process keeps rising its central temperature, 100, 000 degrees, 1 million degrees. Until at some point, in the center of a cloud with enough mass, the temperature reaches about 8 million degrees, and the hydrogen nucleus overcomes the Coulomb repulsion between the protons, starting with the thermonuclear reaction of hydrogen fusion to helium!

Hydrogen fusion kindling marks the official formation of a star. From this moment on, the stars will glow outward by their own thermonuclear reactions.

More importantly, thermonuclear fusion gives stars the energy to continuously counter gravity for the first time, and forms a stable "negative feedback" mechanism: if nuclear fusion is too strong, it will make the star overcome gravitational expansion, thus lowering the temperature and weakening the nuclear reaction; on the contrary, if gravity defeats nuclear fusion and compresses the star, it will lead to a rise in temperature and improve the efficiency of nuclear reaction.

This balance will be maintained until the hydrogen in the center of the star burns out, giving the star a stable luminosity.

Such as the sun, which brings light and energy to the earth.

This is an essential factor in the origin of life.

Helium flash: vigorous, unknown according to the relationship between stellar mass (energy reserve) and luminosity (luminous power), the larger the star, the faster it will burn out the hydrogen inside.

Until then, whether helium can take over this task has become the hope of sustaining the life of the stars. But compared with hydrogen, it is more difficult for helium nuclei containing two protons to overcome repulsive fusion, and helium combustion needs to wait for higher temperature and density.

A star near the end of life (photo: NASA) ▼

As the helium produced by hydrogen combustion continues to accumulate, a shell of central helium core and outer hydrogen continues to burn. Like protostars, helium nuclei will gradually collapse inward, unable to resist their own gravity.

Part of the gravitational energy released by this process is converted into thermal radiation energy, which is injected into the outer layer of the star, like "blowing balloons", causing the star to expand violently, while the temperature decreases and the color turns red. This is the red giant.

A red giant is the later stage of the evolution of stars.

(diagram, figure: Wiki) ▼

For the sun, this process will come in about 5 billion years. At that time, the expanding radius of the sun will be close to the earth's orbit. If human civilization still exists, plans like "wandering the earth" will have to become a reality.

The rapid expansion and aging of the sun is the beginning of the story.

(photo: stills of wandering the Earth) ▼

If the helium in the center of the star can accumulate to a critical value of about 0.45 times the solar mass and its core temperature reaches about 100 million degrees, the reaction of further coalescence of helium into heavy nuclei will finally begin.

But at this time, the density inside the star has also reached an unprecedented size, and mysterious forces from the quantum world are about to intervene in the game of gravitational sawing, adding new uncertainty to the wrestling that takes place inside the star.

In this image, thousands of stars are twinkling in the universe.

(figure: NASA) ▼

In quantum mechanics, microscopic particles are divided into two categories according to the number of spins: bosons with integral spins (such as photons) and fermions with semi-integer spins (such as electrons and neutrons).

The fermion has the famous Pauli incompatibility principle, that is, it is impossible to hold two identical fermions in the same microscopic quantum state.

As a result, in an environment where the density is high enough and the temperature is relatively low, the low-energy quantum states are quickly packed, and other particles are forced by this rule to repel each other and live in a higher-energy state. the pressure caused by this effect is called degenerate pressure.

This principle is one of the basic laws of the motion of microscopic particles.

(figure: Wikimedia) ▼

Five billion years later, when our sun evolved to the stage where helium was ignited, the electrons in the center were already degenerate. At this time, the electron degenerate pressure of the helium nucleus replaces the general thermal pressure and becomes the "main force" against gravitation. But what makes quantum degenerate pressure unique is that its size is independent of temperature.

In this case, the delicate balance between thermonuclear fusion and gravity mentioned earlier no longer exists-when helium fusion is ignited, the core temperature rises and adiabatic expansion occurs, but the degenerate pressure does not decrease. As a result, negative feedback becomes positive feedback, and helium fusion is accelerated at higher temperatures.

As a result, the explosive energy release, known as "helium flash", starts in an instant.

A white dwarf star called Sakurai Star experienced helium flash

(red area below, figure: Wiki) ▼

Fortunately, as the temperature continues to rise, the electrons will break out of the degenerate state, ordinary thermal pressure will become dominant again, and the balance between temperature, pressure, thermonuclear reaction and gravity will soon be restored again. As a result, the helium flash often lasts only a few minutes or even seconds before it comes to an end.

Moreover, because the "helium flash" occurs at the core of the star, the opacity inside the star determines that this intense physical process will not spread to the periphery of the star. This can only be regarded as an "uprising" launched in the interior of the star with the help of the strange power of the quantum, but soon quelled. In fact, it is difficult for us to directly observe and know the information of "helium flashover" in the interior of the star.

Unlike what is described in wandering Earth, we don't have to worry about the catastrophic effects of the sun's "helium flash" on humans, but the real problem is that we have to get the earth out of orbit before the sun becomes a red giant.

At present, the sun is in its prime and is in the main sequence star stage.

This stage will last about 10 billion years.

(figure: Wikimedia) ▼

Ultimate sparkle: what traps me will make me stronger. Calculations show that for stars with more than 2.3 times the mass of the sun, their centers are no longer degenerate when helium fusion is ignited, and helium nuclei will skip the helium flash and begin to burn smoothly. The products of helium combustion are carbon and oxygen.

At this time, the star has two separate burning shells of hydrogen and helium from the outside to the inside, and a core composed of carbon and oxygen is gradually formed at the center. The energy generated by the recontraction of carbon and oxygen nuclei and "double-shell combustion" causes the surface of the star to break free from the gravitational shackles and expand again, becoming a red supergiant.

Betelgeuse, for example, is a red supergiant.

(figure: Wikimedia) ▼

At this time, the outer layer of the star is already turbulent, and the matter convection is so intense that it is even blown directly into space by a strong star wind to form a planetary nebula.

Southern Ring Nebula captured by Weber Telescope in 2022

Like a sapphire embedded in black velvet

(figure: NASA's JWST) ▼

The fate of the core of the central carbon and oxygen star is about to usher in the final trial. If the mass of the star is not large enough, further fusion of carbon and oxygen nuclei cannot occur. It will stay where it is and become a carbon-oxygen white dwarf.

Sirius An and B, Sirius B is a white dwarf.

(small light spot on the lower left, picture: NASA) ▼

If the carbon-oxygen nucleus is larger, or happens to accrete to more mass from a nearby companion star, reaching the Chandra Seka limit (about 1.4 times the solar mass), the nuclear reaction will be triggered again.

But at this time, the electronic degeneracy pressure appears again. The degenerate carbon-oxygen nuclear explosion is more intense than the "helium flash", and all the stones are burned in an instant. Carbon and oxygen are melted into heavier elements at high temperature and high pressure, and are immediately thrown into space with the explosion. At the cost of being shattered, the star core completely gets rid of the shackles of gravity and releases the final light and heat. This is the Ia type supernova.

An Ia type supernova in galaxy NGC 4526

(bottom left light spot, figure: NASA) ▼

G299 Ia supernova remnant (photo: NASA) ▼

If the mass of the star is more than eight times that of the sun, the carbon and oxygen nuclei break away from electron degeneracy, the central temperature has reached 1 billion degrees, and carbon and oxygen burn steadily, synthesizing heavier elements in turn until iron.

Because the specific binding energy of iron is the highest, the normal nuclear fusion stops here. If we roam inward from the surface of the star at this time, we can see an onion-like shell of hydrogen, helium, carbon, neon, oxygen, magnesium, silicon and other elements, eventually reaching a high-density iron core.

Before the core collapses, the core structure of a massive star

(schematic only, not according to scale, figure: Wiki) ▼

As nuclear fusion stops, the last gravitational collapse is inevitable. The collapse of the iron core will detonate the entire core of the star and forge elements heavier than iron. In this process, a large number of neutrinos are released. The explosion of such massive stars is also known as nuclear collapsing supernovae.

SN 1987A supernova explosion (figure: NASA) ▼

Finally, the extremely compressed core becomes an extremely dense neutron star or even a black hole. The gravity of a black hole will mercilessly engulf everything, including light. The neutron star once again seeks the shelter of quantum degenerate pressure, but it is also limited to self-protection.

At this point, all the energy that can be relied on has been exhausted, and there is no longer any force to resist gravity. So this time, it is "life imprisonment".

PSR B0531y21 is a quite young neutron star.

It is located in the Crab Nebula (photo: NASA) ▼

By the way, take a look at the Crab Nebula (photo: NASA) ▼

Stars are born in the disturbance of gravity, and they are bound by gravity all their lives, and dance by gravity, shining out the most gorgeous fireworks in the universe. Every ray of light it emits is proof that it can compete with gravity.

But is there really no new hope?

If a neutron star retains its magnetic field and angular momentum, it will become a pulsar. Pulsars are called the "beacons of the universe". They rotate tirelessly at a fixed frequency and emit radio pulses. It is like an eternal monument, in the direction of the pulse sweeping, to tell the universe the story that once existed.

A pulsar is a star that blinks.

Pulse cycle from the Vela pulsar (figure: Wiki) ▼

The 500m aperture spherical radio telescope is a sharp weapon to search for pulsars.

(Chinese Heavenly Eye) ▼

Today, after the forging of the previous generation of stars, the universe has prepared all the chemical elements necessary to make up our bodies. When the aftermath of the supernova dies down, the nebula in the universe will be slowly summoned by gravity again, and the potential of hydrogen and helium nuclei will be awakened again, releasing a dazzling brilliance to the universe.

Around the newly formed stars, there are dust, gas, free electrons, photons, magnetic fields and cosmic rays rich in chemical elements. Will condense into planets under the complex action of electromagnetism and gravity.

In the star formation region of the Cygnus Sh2-106,

This epic intersection may be taking place.

(horizontal screen, picture: NASA) ▼

Tarantula Nebula, delicate, unknown, bizarre (Photo: NASA) ▼

Perhaps on one of the suitable planets, matter will combine organically and begin to replicate and reproduce itself. After hundreds of millions of years (this time is only an instant in this article), wisdom and civilization evolved, and in their language, they named their planet "Earth" and their star "Sun".

Like the cycle of life, this magnificent and magnificent story told in this article is not only the future that we are going to happen, but also the past that has already happened.

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