Imagine this:
Among the stars in the depths of the universe, there is an inconspicuous star that suddenly becomes incomparably bright, and the light emitted becomes ten million times stronger in an instant, and can even illuminate the entire galaxy in which it is located. The explosion of its last moments of life, producing a strong radiation capable of destroying all life, frantically sweeping through the corner of the universe...
Figure Supernova Explosion Imagination Figure Source | Science News
This is the supernova explosion, one of the most magnificent wonders in the universe.
However, this explosion at the end of life is not the end, a journey to conceive a new life is about to begin, and the specific process, let's slowly walk into the supernova, starting with understanding the physical processes associated with it.
1
The brightest star in the night sky
As early as 185 AD, a supernova illuminated the night sky of the Earth, attracted attention and was recorded - this is SN 185. It is recorded in the Book of the Later Han Dynasty, but because of its age, there are not many descriptions of it.
Another supernova, SN 1006, is more well-known — it shone in the skies of the Song Dynasty and medieval Europe for 24 months, even brighter than the moon at its brightest, giving countless stargazers around the world a multitude of conjectures.
Figure Simulation of the SN 1006 outbreak Source | Tunc Tezel
When humans entered the era of astronomical telescopes, observing supernovae became simpler, and people no longer needed to observe with the naked eye this spectacle that was once in fifty years throughout the Milky Way. And people's understanding of supernovae has also gradually deepened with the development of science and technology, and they have also understood the causes of supernovae: it turns out that most of these stars with extraordinary brightness but cannot last long are massive stars that are about to end their lives.
We know that such a huge celestial body as a star has a very large internal pressure due to gravity. According to the principle of thermodynamics, an increase in pressure leads to an increase in temperature as well. As a result, the star's hottest core ignites a nuclear reaction, releasing energy against its own gravitational collapse.
However, years of burning have produced many nuclei that cannot be burned temporarily, and these nuclei are piled up in the core of the star because they are relatively heavy, affecting the rate of combustion. Slowing down the burn will cause the star to be further compressed, the core temperature to continue to rise, and eventually ignite the fusion reaction of the heavier core in the core.
When the cores of very massive stars (typically greater than 8 times the mass of the Sun) are ignited, the products generated are piled up to form new cores, which are then ignited, and so on several times until there is no more nuclear reaction available to provide energy, and a great collapse begins: the cores of the stars compress under their own enormous gravity, but there is no energy to fight them, and soon the matter is compacted, and the electrons of the atoms begin to rely on electromagnetic repulsion to fight gravity. However, this confrontation is futile in massive stars, and under great pressure, electrons are also pressed into the nucleus, and the entire core becomes a ball composed entirely of neutrons.
Generally speaking, this collapse ends here. But if the star is too massive (typically greater than 14 times the mass of the Sun), then even the repulsion between neutrons cannot resist gravitational compression. With the loss of the last line of defense, the entire core fell into the center point, forming a black hole that the light could not escape. In the process of this core collapse, so much energy is released in a short period of time that a violent explosion can be formed, blowing the material of the star's crust directly and completely, emitting a light that is even equivalent to the total amount of light it emits in its lifetime.
Figure SN 1987A Before the outbreak (right) versus post-outbreak (left). The source of the image is | NASA
At this point, a gorgeous supernova explosion comes to an end, the neutron star or black hole formed by the core slowly cools in the embers, and the shell that is blown up will form a fluffy nebula, waiting for the next convergence.
2
Death, or new life?
The supernova explosion is not only the end of life, but also the beginning of life. This magnificent explosion can be called a cosmic epic that created the world.
It should be explained that the world here refers to the colorful stars in the universe- planetary systems, including a variety of living civilizations that may exist on the planets.
Let's start with the concept of nucleosynthesis. Our colorful world is made up of elements, and the most fundamental difference between elements is the difference in atomic nuclei. According to the currently accepted Big Bang theory, the universe originated from a big bang, and the products of the big bang are only a few light nuclei, such as hydrogen, helium, and a small amount of lithium. However, there are many kinds of elements from hydrogen to uranium on the earth, how did these elements come from?
Supernovae are the source of most of the heavier elements.
The supernova mentioned earlier will continue to form a core before the explosion and continue to be ignited, which is actually a process of nuclear synthesis. Light nuclides burn and synthesize heavier elements until iron— because the fusion reaction of the iron nucleus no longer releases energy but absorbs energy, so conventional nuclear synthesis is over.
However, the supernova show has only just begun. During the great collapse, sufficient energy and abundance of neutrons initiate the r process (fast neutron capture process). The nucleus constantly captures neutrons to increase mass, making it possible to synthesize elements above iron. In this storm of rapid nuclear synthesis, places that are generally difficult to break through because the synthesis rate is lower than the decay rate will be broken, and then a large number of heavy elements (including heavy metals such as silver and gold as we know it) will be synthesized. These heavy elements are ejected with supernova explosions and float in the nebulae, providing the material basis for forming our colorful world.
Figure Schematic diagram of multiple cores in the interior of a star before a supernova explosion Source | University of Oregon
Nucleosynthesis provides the foundation, but the effects of supernovae are far from over. The nebula produced by the eruption will give birth to the next star, just like the legend of Pangu's opening of the world. The heavy elements in the nebula converge to form a core, some of which gather larger and larger, and eventually rekindle the nuclear reaction to form new stars; the small cores rotate around the stars to form planets, and the stars are combined to form galaxies, just like the solar system we know. At the same time, the high-energy particles ejected by the supernova explosion will also bring waves and disturbances to the calm nebula it reaches, accelerating the speed at which the nebula converges. Some studies believe that our solar system was formed by the ripples of supernova explosions.
From this point of view, supernovae not only provide the material basis (elements) of world formation, but also provide hotbeds (nebulae), and even get up services (perturbations) are provided, which is simply a perfect one-stop service!
The crab-shaped nebula formed by supernova explosions - this is the galaxy's new source | NASA
As physicist Lawrence Klaus put it:
“
Every atom in your body comes from a supernova, and the atoms in your left hand and the atoms in your right hand may come from different stars. This is really the most poetic thing in physics I know: everything about you is stardust...
”
Most of the elements in our bodies come from the nebulae of supernova explosions, and the vast majority of carbon and oxygen elements and trace elements other than hydrogen are synthesized and released by supernovae. In fact, not only us, but almost everything around us comes from the stars, from the magnificent supernova explosions of hundreds of millions of years ago.
Supernova, this short and shining cosmic wonder, can be said to be a well-deserved cosmic epic that created this colorful world!
The author | Tian Ning
Edited by | Liu Fang
exegesis:
1. This article mainly introduces a core collapse supernova, which is a supernova explosion phenomenon formed by a massive single star due to core collapse. There is also a supernova formed by a close binary accretion system (type Ia supernova), in which a white dwarf absorbs enough material from its companion star to raise its core temperature to the condition of carbon combustion, and eventually undergoes rapid nuclear fusion and completely disintegrates.
bibliography:
[1] C. E.Rolfs, W. S. Rodney. Cauldrons in the Cosmos ( Univ of Chicago Pr, 1988).
[2] C. Iliadis, Nuclear Physics of Stars ( Wiley, Weinheim, 2007)
The reproduced content represents the views of the author only
Does not represent the position of the Institute of Physics, Chinese Academy of Sciences
Source: Institute of Modern Physics, Chinese Academy of Sciences
EDIT: just_iu
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