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

As we all know, diamonds are not rare in the universe, heavy metals such as gold are really rare. Generally speaking, the heavier elements are formed under more stringent conditions. For elements above iron, nuclear fusion within the star is no longer enough, and more extreme conditions, such as supernova explosions, are needed. But in fact, the gold we usually come into contact with may come from an even rarer event in the universe-neutron star collisions.

Neutron star collisions (concept map) back at the beginning of the Big Bang, there was almost only hydrogen and helium in the universe. With the emergence of stars, heavier elements begin to be produced through fusion reactions within the star. As long as the star is large enough, this "element factory" can produce almost all the elements below iron, but it will be difficult to move up, because the subsequent fusion reaction is not to release energy, but to absorb energy.

Helium-3 fusion reaction, so if you want to continue to produce heavier elements, you have to improve the "production process". In the previous fusion reaction, two lighter nuclei were brought together to become heavier nuclei, while the improved process was to insert neutrons directly into the nuclei, which is called "neutron capture".

But with only one more neutron, the proton and atomic numbers do not change. At best, heavier isotopes are produced. But for some isotopes, they are unstable and there is usually beta decay. For example, neutrons in iron-59 have a certain probability of decaying into protons by releasing an electron. In this way, the atomic number is + 1 because the nucleus has one more proton, so the original iron-59 becomes cobalt-59. In the same way, cobalt can continue to change from cobalt-60 to nickel-60 with a larger atomic number, and so on.

Although neutron capture can in principle continue to produce heavier elements than iron through this improved "production process", the neutron capture that occurs inside the star is very weak and inefficient, so it is also called "slow neutron capture" (because the kinetic energy of these neutrons is small).

Slow neutron capture is like a laboratory technology that has just been developed. Although it points out the "technological direction" for the element factory of stars, it cannot be used for "mass production".

However, the octogenarian star does not have that much time, so this time it decided to burn its bridges and fight for the last glimmer of strength, and finally it found the legendary way of "fast neutron capture"-supernova explosion.

Supernova explosion (concept map) A large number of neutrons are released in the form of extremely high energy in this "fireworks show" that is enough to illuminate the galaxy. Under the impact of these high-energy neutrons and beta decay, the previous nucleus became a copy of experience and began to upgrade crazily, so a large number of heavy metal elements were produced.

Although supernova explosions produce large amounts of heavy metals, because most of them are concentrated in the core of stars, not much can actually be used for us. It's like to ensure scarcity, I produce it, but I just don't sell it.

Is the heavy metal industry monopolized by supernovae? Certainly not.

Among the stars that have become debris, a few "conscientious" neutron stars have decided to break the monopoly. It's just that at this time, it has exhausted the last trace of strength and can no longer realize its wishes on its own. But the good thing is that it is not a person, it also has a like-minded brother.

In 2017, gravitational wave observatories LIGO and Virgo simultaneously observed an event called GW 170817. Unlike the previously observed merging signals of two black holes, astronomers also received corresponding electromagnetic signals, such as brief gamma-ray bursts, shortly after the gravitational wave signal was received.

After analysis, scientists found that this is a rare double neutron star merger event. Through the analysis of the spectral lines of the electromagnetic band, scientists saw the production of elements in this process: in addition to ordinary metal elements, this event also produced a large number of heavy metal elements, such as gold produced several times the mass of the earth. It is said that the global gold price even fell sharply at that time because of this news.

Neutron star collisions are rarer than supernova explosions. Its total energy release is very high, but most of it is concentrated outside the visible band, so it is not as bright as a supernova. However, compared with ordinary novae, neutron star collisions are still thousands of times brighter, so this phenomenon is also known as "thousand novae" or "giant novae".

Why are thousand novae rarer than supernovae? If you think about it, the neutron star is the product of a supernova explosion, plus it must be in a binary system, and the companion star will eventually be a neutron star or a black hole. Even that is not enough, because when a typical supernova explodes, the energy it releases is likely to blow up its companion star, making it difficult for the two to collide again. Unless there is a case, they are rare "super-stripping supernovae" (Ultra-stripped supernovae).

The so-called superstripping supernova is a star that has lost a lot of mass before the explosion, and when it has another supernova explosion, it will be much less powerful so as not to kick its brother away.

The whole process goes something like this:

In a binary system with two massive stars, the larger one is the first to reach the end of life. At this time, its outer layer expands so much that a large amount of material is sucked away by the companion star and eventually peeled off into a core with only a small amount of helium cladding left. The star, which was stripped of its core, then made a supernova explosion, but the impact of the explosion was limited due to lack of matter.

However, although the companion star was not blown up, life was not easy either. After all, "you always have to pay it back." under the strong gravity of the newly formed neutron star, the material previously sucked from the other side has now been sucked back by the other side. With the massive loss of outer material, the companion star was gradually stripped off to its core, followed by another supernova explosion.

After the baptism of two explosions, only two withered neutron stars are now orbiting each other. As the two sides get closer and closer, orbital energy begins to be released in the form of gravitational waves. Before the final collision, the two neutron stars can orbit at a speed of hundreds of times per second. Finally, the collision occurred and a thousand nova was born.

When two neutron stars come into contact with each other, they theoretically merge into a supermassive neutron star and then collapse rapidly into a black hole in milliseconds. This process is accompanied by a very high energy release, when the previous fast neutron capture comes into play again. But this time the reaction is no longer limited to the core, so a large amount of heavy metals can be transported to the vast interstellar space around them.

As a result, the monopoly of heavy metals in the universe is broken, and then the newly formed stars are no longer as malnourished as the original stars, and this time they are relatively rich in metal elements, although the content is still not high. However, the ability of "fast neutron capture" has been inherited by new stars as a "traditional craft".

Over the course of generations, 4.6 billion years ago, next to a yellow dwarf star in the spiral arm of Orion in the Milky way, a rocky planet with a metal core was born. Its name is Earth.

This article comes from the official account of Wechat: Linvo says ID:linvo001, author: Linvo

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