[Unsolved Mystery]Is Betelgeuse Next? | Swing | Stars | Sun

Hello everyone, I’m Fuyao, welcome to explore the unsolved mysteries with me.

In the summer of 2020, the Pan-STARRS telescope at Haleakala Volcano on Maui Island, Hawaii suddenly detected a large amount of radiation, and the emission source came from the NGC 5731 galaxy about 120 million light-years away from the earth. The red supergiant star that has finished its life process is violently ejecting gas. A few months later, in the fall of 2020, a supernova lit up the sky, which scientists named Supernova 2020tlf (SN2020tlf). This is the first time in history that astronomers have witnessed the entire process of a red supergiant going supernova in real time.

Speaking of supernova, if you just look at the name, you may think that a supernova is also a kind of star. In fact, it is just a violent explosion experienced by a star when it is nearing the end of its evolution, and its brightness is very dazzling. We’ll go into detail in a moment.

The predecessors of red supergiants are stars, so people can’t help but ask, what will be the future fate of our sun, and will it eventually explode into a supernova? What will happen to the earth then? There has also been a change in Betelgeuse, which is very close to us. Is it going to explode as a supernova? Today, we are going to talk to you about these issues.

evolution of stars

Let’s start with the birth of stars. All stars are born in a huge nebula. How big is it? A typical nebula is about 100 light-years across and contains about 6 million times the mass of the Sun. When the nebula is fragmented due to various reasons, it will split into smaller and smaller fragments. A large number of low-temperature air masses shrink due to their own gravity, their density increases, and the gravitational potential energy is converted into heat energy, thereby releasing a lot of heat, so finally The debris condenses into superheated swirling balls of gas called protostars. According to the Buddhist saying of “formation, cessation, destruction and cessation”, stars are in the early stage of “formation”, just like a baby has just been born.

After that, the stellar baby entered the growth stage. It continues to attract and accumulate interstellar gas and stardust in the nebula. For a star of the same mass as the sun, this growth process takes about 100,000 years. Afterwards, the protostar evolves into different bodies depending on its final mass.

A protostar with a particularly small mass, less than 0.08 solar mass, becomes a “brown dwarf”. Brown dwarfs are awkward because they are too big to be called planets and too small to be called stars. The light it emits is dim, gradually cooling and disappearing into visible light over hundreds of millions of years.

Protostars with a mass within 8 solar masses will become “low-mass stars”, and those with heavier masses will become “massive stars”. And the future development of the two will be very different.

At this stage, the star is in a stable period, that is, the period of “living” in the process of “forming, living, destructing,” and is called the main sequence star. A star will spend most of its life in the main sequence phase.

the future of the sun

The energy that supports a star throughout its life is hydrogen. The more massive the star, the faster the hydrogen consumption, so the shorter the life. According to the current calculations of the scientific community, a star like the sun has a life of about 10 billion years. Now it is estimated that the sun is about 4.5 billion years old, so it should be said that it is in its prime. So what will the sun look like in another 5 billion years?

According to the existing theoretical deduction, the color of the sun will become more and more red from the current yellow and white, and the volume will become larger and larger, and finally the diameter can be 256 times the current size, becoming a red giant star. At that time, the planets in the near future, including Mercury, Venus, and Earth, will all be swallowed by the sun.

However, humans on earth may not be able to see this day, because scientists predict that in about 3 billion years from now, the surface of the earth will become as hot as Venus. In billions of years, Earth’s air will escape into outer space, eventually turning into a charred planet. That is to say, until the earth is swallowed by the sun, human beings will no longer be able to survive on the earth. Therefore, interstellar immigration should be as early as possible.

Going back to the sun, after it becomes a red giant star, after it has finally used up all its fuel, it will continue to collapse inward, and finally become a white dwarf. White dwarfs are very, very dense. A white dwarf as heavy as the sun has a radius of only about 1% of the sun. To put it more figuratively, a teaspoon of white dwarf material weighs about 5.5 tons, which is heavier than the heaviest Asian elephant.

supernova explosion

In single-star galaxies like the solar system, the ultimate fate of a star that becomes a white dwarf is to use up all its energy and become an icy, dark black dwarf. But most of the galaxies in the universe are actually connected galaxies, which are two or more galaxies orbiting each other. Such as the Sirius binary system.

If such a galaxy, one of its primary stars becomes a white dwarf, it absorbs the energy of the companion star. The absorbed energy will be turned into gas and pulled to a large disk around the white dwarf, and then the gas will rotate around the white dwarf. superior.

If the white dwarf becomes more and more massive, it may reach its mass limit, the Chandrasekhar limit, which is about 1.4 solar masses. Beyond this mass limit, the white dwarf collapses further into a denser neutron star. But the process was astonishing. why? Because the white dwarf will explode in a supernova, emitting a large amount of electromagnetic radiation, emitting a dazzling light, the brightness of this light even exceeds the brightness of the entire large galaxy, this process may last for weeks to months or even years before gradually decaying. So how much energy is released? Scientists believe that the radiation energy released by a supernova can be comparable to the sum of the energy radiated by the sun in its lifetime.

There are also many supernova explosions. For example, the explosion of a white dwarf star because its mass exceeds the limit is called a type Ia supernova. What’s so special about it? Because it is all white dwarfs exploded at the same mass point, the power and luminosity of the explosion are basically the same, which provides a sight for scientists to measure the distance of cosmic celestial bodies. Astronomers call it standard candlelight. That is, by measuring Type Ia supernovae in different galaxies, it is possible to know how far the galaxy is from us.

In addition to this form of supernova explosion brought by white dwarf stars, there is another type, which we introduced at the beginning of the program, which is formed by the direct explosion of “red supergiants”.

We just said that when a star enters an old age, it will become a “red giant”. And if the star is a “massive star” with a lot of mass, it will become a “red supergiant”, and the more massive it is called a “red hypergiant”.

The supernova explosions brought by “red supergiants” and “red supergiants” can be said to be even more terrifying, because they will not only produce neutron stars, but even “explode” black holes.

Neutron stars and black holes

Let’s talk about neutron stars first, which can be said to be very mysterious stars with super-super dense density. There are no electrons or nuclei in it. Because of the extremely high pressure, not only the outer shell of the atom is crushed, but even the nucleus of the atom can be crushed, and both protons and neutrons are squeezed out. Protons meet electrons and combine into neutrons. In this way, only neutrons are left in the entire star. Let’s use an analogy. The density of a neutron star is 1 billion tons per cubic centimeter, which is like pressing the Himalayas into a cube of sugar.

The neutron star rotates extremely fast, and the two magnetic poles emit extremely strong radiation, and almost no life can survive wherever the radiation goes. Because the magnetic axis of some neutron stars does not coincide with the rotation axis, various radiations such as radio waves generated when the magnetic field rotates may be transmitted to the earth in a flashing way, just like a beacon, which is called a pulsar. Please pay attention, not all neutron stars are pulsars, and some neutron stars do not have pulsars. Likewise, not all pulsars are neutron stars, as some white dwarfs do. It is said that when the pulsar was first discovered, people thought it was a signal from aliens, but later they realized that they thought too much.

If the neutron star continues to absorb mass and collapse beyond the Oppenheimer limit, it will create a black hole. And if the mass of the “red supergiant” that exploded supernova exceeds 20 times the mass of the sun, then it is very likely to directly produce a black hole after it explodes.

Black holes are “monsters” in the universe. The space-time around them is extremely distorted and has an extremely strong gravitational force, so that all particles, even electromagnetic radiation such as light, cannot escape. A new paper published in the Astrophysical Journal shows that according to research models, there are about 400 billion black holes in our visible universe, or 4X10¹⁹.

After a black hole is formed, it can continue to grow by absorbing material from its surroundings. The masses of black holes discovered by scientists are basically at two extremes: one is a stellar-mass black hole, which is about 10-24 times the mass of the sun; the other is a super black hole, and the center of each galaxy is occupied by such a black hole. Super black holes can be millions to billions of times the mass of the sun.

The reason for the formation of super black holes is still a mystery. Some astronomers have discovered the merging behavior of black holes, so it is speculated that black holes may become super black holes by absorbing other stars and merging with other black holes. But let’s be honest, if the black hole at the center of every galaxy formed like this, how long the whole process would be.

Will Betelgeuse become a supernova?

So are there any candidates for supernova explosions in our galaxy? Have. That’s Betelgeuse on Orion’s shoulder. Betelgeuse is a distinctly bright red star and one of the most recognizable stars in the night sky. It is 640 light-years away from Earth and has 12 times the mass, 900 times the radius and 700 million times the volume of the sun. If Betelgeuse is moved to the position of the sun, it can swallow Jupiter.

Betelgeuse is very young, only 10 million years old. But do you still remember what we said before, the larger the size of the star, the shorter the lifespan? So it has already burned out the hydrogen in the core, and now it has entered the first step of becoming a supernova – becoming a red supergiant. From the end of 2019 to the beginning of 2020, the brightness of Betelgeuse once fell to the lowest point in history. At the time, some people thought that this was probably the prelude to the supernova explosion of Betelgeuse.

So many people fell into panic because of this, why? As we said before, the radiation energy released by the supernova explosion is very strong, and the neutron star or black hole formed by it will also release super radiation. If the eruption is very close to the earth, then there is a good chance that it will destroy the earth’s atmosphere. The astrophysics research team at the University of Illinois at Urbana-Champaign pointed out that at the end of the Devonian period 359 million years ago, the earth suffered one of the largest mass extinction events, and this event is likely to It is caused by supernova explosions outside the solar system. If a supernova explosion occurs in Betelgeuse, will it bring another biological extinction to human beings?

Amid all the speculations, doubts, and research of everyone, in April 2020, Betelgeuse returned to its original brightness. Everyone is even more curious, what happened to it?

Later, a paper published in the journal Nature solved the mystery of Betelgeuse’s dimming. The team thinks that sometime before this dramatic dimming of Betelgeuse, the star pulsed out a huge bubble away from it under the outward pulsation, and when an area of ​​the surface cooled down shortly thereafter, the temperature increased. Down enough to allow the heavy elements in the gas to condense into the solid dust that causes Betelgeuse to appear dark. It seems to be a false alarm.

However, Betelgeuse is destined to undergo a supernova explosion. The key is when? It depends on what material is burning in its core, helium? carbon? silicon? Betelgeuse will only explode when the fusionable material at its core is exhausted, leaving behind only iron, nickel and cobalt.

A research team from the Australian National University (ANU) analyzed Betelgeuse through stellar evolution, hydrodynamics and mathematical modelling, and concluded that it is in the stage of burning helium, so Betelgeuse may at least still exist. 1 million years.

Moreover, even if Betelgeuse explodes, you don’t have to worry, because Betelgeuse’s rotation axis is still more than 30 degrees different from the direction of the solar system, and the super-strong rays emitted by the magnetic poles will not be directed towards the earth. So, friends who are worried about the mass extinction caused by Betelgeuse can rest easy.

Well, today’s sharing is here, the unsolved mystery, I am Fuyao, see you next time.

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