Will Sirius explode as a supernova? What will happen if it explodes? How much impact will it have on humans?

This title may look a bit scary, but please rest assured that this article is only intended to popularize some basic astronomical knowledge by asking whether Sirius will explode. As for whether Sirius will explode and when it will explode, you will naturally understand after reading this article.

The reason why Sirius is brought up is that Sirius is really special. It is the brightest star in the night sky and it is a star system very close to us.

Let's first talk about the difference between stars and planets

Sirius is the brightest celestial body in the night sky, referring to the stars. In fact, Sirius is not the brightest star we can see in the night sky, because there are several planets that are brighter. Stars are celestial bodies that can generate heat and light by themselves. They are celestial bodies that are tens of thousands of times more massive than planets. For example, the sun is the only star in the solar system, and its mass is 330,000 times greater than that of the earth.

Therefore, planets are satellites of stars and do not emit light themselves, but only reflect sunlight. However, because they are very close, they appear brighter. For example, at night, we cannot see distant self-luminous lights, but can see nearby non-luminous objects such as houses. This is the reason.

The only planets that are brighter than Sirius that we can see with our naked eyes are Venus, Jupiter, Mars, and Mercury. The Moon is not a planet, but it is the closest planetary satellite to the Earth and the brightest object in the night sky.

Generally speaking, stars are very far away, and their distance from us is measured in light years.

One light-year is the distance that light travels in one year, which is about 9.46 trillion kilometers. The nearest star to us is Alpha Centauri, which is 4.3 light-years away. It is a triple star system. Among the 10 star systems closest to the sun, Sirius ranks fifth (in terms of star systems, binary and triple star systems only count as one position).

Most of the 10 star systems closest to us are red dwarfs, that is, stars with much smaller mass than the sun. Only the Alpha Centauri system has two stars that are comparable to the sun. Sirius has the largest mass among the 10 star systems, so it is the brightest.

There are four endings to stellar evolution, and supernova explosions will produce two

There are generally four endings at the end of stellar evolution: 1. Red dwarfs that are much smaller than the sun have a very long lifespan and will slowly burn out their fuel before going out, becoming a black dwarf. 2. Stars that are similar in mass to the sun or less than 8 times its mass will undergo a red giant expansion at the end of their evolution. The outer gas will gradually diffuse into space, leaving a white dwarf in the center. 3. Stars that are more than 8 times the mass of the sun will undergo a supernova explosion at the end of their evolution. After the smoke clears, a dense neutron star will remain in the core. 4. Stars that are more than 30 times the mass of the sun will directly leave behind a black hole after a supernova explosion.

Among the 10 star systems around the sun, there is no star that is more than 8 times as massive as the sun, and Sirius is no exception. But why did Sirius explode? This is because in addition to the mass of the star itself, there are several other factors that determine the supernova explosion, the most common of which is the Type Ia supernova explosion.

This explosion is caused by the mass of the white dwarf exceeding the upper limit, which will cause a big collapse, thus causing thermonuclear runaway and explosion. Although Sirius has a small mass, its B star is a white dwarf, which is the source of danger.

What is a supernova?

A white dwarf is the corpse of a dead star. The nuclear fusion in its core has stopped. Without an energy source, it will only cool down slowly. After a long period of cooling, it will eventually go out and become a black dwarf.

But some white dwarfs are not willing to die quietly like this, and will explode again when they have the chance, making some noise and showing their presence. This kind of presence is a supernova explosion, which I call "resurrection".

This is because the white dwarf is not a stable corpse. Its existence follows the Pauli exclusion principle, relying on the electron degeneracy pressure to barely support its own gravity. The Pauli exclusion principle is a physical law that states that fermion particles (including electrons, neutrons, protons, etc.) have the property of mutual repulsion. As long as these particles are close to a certain degree, the incompatibility law occurs.

White dwarfs have large mass and small volume. A white dwarf like Sirius B has a mass more than 1 times that of the sun and a volume only as big as the earth. Therefore, the density of the matter is extremely high, reaching several tons per cubic meter and centimeter. This kind of matter is no longer the matter we normally know.

The huge gravitational centripetal pressure of the white dwarf flattens the atoms, and the electrons outside the nucleus leave their original orbits and become free electrons, which are squeezed to a level closer to the nucleus. The electrons tend to be squeezed together, and the strong repulsive force (pressure) between electrons, also called electron degeneracy pressure, resists the huge gravitational pressure, allowing the nucleus to remain intact and float in the ocean of free electrons, thus maintaining the star shape of the white dwarf.

But there is a limit to the electron degeneracy pressure, which is called the Chandrasekhar limit. When the mass of a white dwarf reaches 1.44 times that of the sun, the electron degeneracy pressure can no longer support the gravitational pressure, and the entire planet will collapse. The huge centripetal pressure will cause the core temperature to rise sharply, thereby stimulating carbon nuclear fusion.

Nuclear fusion occurs within seconds, causing a thermal runaway reaction inside the white dwarf. Huge amounts of energy are released instantly, blowing the white dwarf to pieces and turning it into a la supernova. Because the energy of all la supernovae is the same, they become standard candles in astronomical observations, providing an important basis for celestial observations and distance calculations.

Why did Sirius explode into a supernova?

The main cause of the trouble is Sirius B. As mentioned earlier, as long as a white dwarf reaches 1.44 times the mass of the sun, it will explode as a supernova. The current mass of Sirius B is only about 1.1 times that of the sun. If it continues to maintain this state, it will not explode but will slowly die. The problem is that it is only 300,000 kilometers away from its partner Sirius A.

The super strong gravity of the white dwarf will devour all the interstellar matter around it. Of course, Sirius A is still so far away that theoretically it will not be accreted by Sirius B, but the problem is that when Sirius dies, it will become a red giant and will throw away most of its own mass.

When Sirius A becomes a red giant, its radius will expand to 200 to 300 times its original size. Sirius A's radius is now about 1.7 times that of the Sun. The Sun's radius is now about 696,000 kilometers, while Sirius' radius is 1.19 million kilometers. After becoming a red giant, its radius will be about 140 million to 200 million kilometers.

It seems that the distance between the two stars is still very large, and Sirius B still seems to have no advantage over Sirius A. But we must not forget that the red giant will expand and expand, and the outer matter will drift into space. In the end, Sirius A will only leave a white dwarf corpse in the core, which will only have a size of about 0.6 solar masses, and the remaining 1.4 solar masses of matter will flow into space.

At this time, Sirius B's chance came. Matter floating near it will inevitably be pulled by its strong gravity, and its mass will continue to increase. Sirius B is now about 1.1 times the mass of the sun. If it increases by a little more than 0.3 solar masses, it will reach the Chandrasekhar limit. Will Sirius B absorb so much mass?

Maybe, maybe not. That's why Sirius may explode in the future. Of course, Sirius still has 1.5 billion years to live, so this explosion will not happen until 1.5 billion years from now.

The energy of the Sirius LA supernova explosion and how it feels on Earth

How much energy does a supernova have? It is generally believed that at the moment when a white dwarf exceeds the Chandrasekhar limit, most of the carbon and oxygen will condense into heavy elements within a few seconds, the internal temperature will instantly rise to billions of degrees, and the energy of the thermonuclear reaction will be greater than 10^44J (joules).

The energy of solar nuclear fusion is 3.78*10^26J, which means that the energy of a supernova explosion will reach 26.5 trillion times that of the sun, which means that there are 26.5 trillion suns shining on us. This huge energy will instantly blow the white dwarf to pieces and eject each particle outward in the form of shock waves, with a speed of 5,000 to 20,000 kilometers per second, and the maximum speed is nearly 7% of the speed of light!

The absolute magnitude at the time of the explosion could reach -19.3, which is 4.5 billion times brighter than the sun.

If this explosion occurred at the position of the sun, the earth would be vaporized without a trace. But after all, it happened 8.6 light years away from us. The light waves would reach the earth 8.6 years after the explosion. If there were still humans on earth at that time, people would be able to see a dazzling star.

If the shock wave maintains the speed of the explosion, it will take 122 to 505 years to reach the solar system.

The conversion formula between apparent magnitude and absolute magnitude is: m=M-5log(d0/d), where m represents the visual magnitude, M represents the absolute magnitude, d0 is 10 arc seconds (about 32.6 light years), and d is the actual distance of the celestial body (in light years).

Therefore, according to the formula, the apparent magnitude of the Sirius supernova can reach -22.2 when viewed from Earth. The apparent magnitude of the Sun is -26.7, and the apparent magnitude of the full moon is -12.7. The smaller the apparent magnitude, the brighter it is, and the more negative it is, the brighter it is. The brightness of each level differs by 2.512 times. Therefore, the Sirius la supernova seen by Earthlings is a bright star that is 1288 times brighter than the Moon and 63 times less bright than the Sun.

It is like a small sun, hanging in the sky both day and night (at the right angle), and the night is just like a cloudy day, so you don't need lights to read. But this little sun that looks a bit dazzling will not harm the earth's ecology. The real harm will come from the high-energy particles from supernova explosions that will enter the solar system in 122 to 500 years.

The impact of the supernova explosion of 8.6 light years away on the Earth's ecology

High-energy particles from the sun attack the earth every day in the form of solar wind, but due to the resistance of the earth's magnetic field, most of them flow away along the magnetic lines of force. Only in the weak magnetic fields at the poles can a little bit of them take advantage of the opportunity to enter. Therefore, we can see the brilliant light emitted by the game between the atmosphere and the solar wind. This is the aurora.

The energy of the solar wind is not very large, with a maximum speed of only 800 kilometers per second. These solar charged particles will form a heliosheath layer on the periphery of the solar system to resist the invasion of interstellar rays. However, the energy wind of a supernova explosion, that is, the particle shock wave, has a maximum speed of 20,000 kilometers per second, which the solar heliosheath is obviously unable to resist.

This will inevitably impact the Earth's magnetic field, which becomes very weak under this impact and is difficult to resist, so these energy particles will inevitably invade the Earth's surface. If there are still humans at that time, they will see colorful lights all over the sky, which is a desperate game between the atmosphere and the charged particles.

Ultimately, these particles are likely to destroy the atmospheric ozone layer. The high-energy particles that are not blocked by the atmosphere will intensively attack the Earth's organisms and penetrate the DNA molecular bonds of the organisms, making it difficult for the Earth's ecology to escape.

Fortunately, even if a supernova explosion like Sirius really happens, it will be 1.5 billion years later, and it is hard to say whether humans will still exist by then. If humans can really survive that long, after more than 1 billion years of evolution and development, they will have migrated outside the solar system and become a multi-planet species. Avoiding and responding to such natural disasters will be a piece of cake.

Therefore, we don’t have to worry about how future generations will deal with the Sirius catastrophe.

In fact, the supernova explosions that may be seen by humans are the several red giants that have been observed, such as Eta Carinae and Betelgeuse. The explosions of these red giants are likely to occur in a relatively short period of time, and they may have already exploded, but the light has not yet reached us.

The energy exploded by these red giants is much greater than that of the Sirius la supernova, but these stars are hundreds or even thousands of light years away from us. As long as there is no gamma-ray burst that sweeps the Earth, it will not have a major impact on the Earth's ecology.

That’s all for now. Welcome to discuss and thank you for reading.

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