How are black holes formed? How many black holes are there in the universe? How many black holes are there in the solar system?

According to the research of scientists, there are about 90% dark matter in the universe.

Generally speaking, in the universe, celestial bodies with a certain mass generally exist in the form of stars, while black holes are celestial bodies with unusually high density and gravity formed by the death and collapse of massive stars under their own huge weight. Therefore, as long as there is a star with enough mass, it is likely to form a black hole after death. And there is no shortage of massive stars in the universe.

So there must be many black holes in the universe.

Limited to the current level of science and technology. Finding black holes is still an arduous task.

At present, there are only the following black holes that we have discovered: the black hole of Sagittarius A* in the center of the Milky Way and the black hole of Andromeda galaxy are similar to the formation process of neutron stars; The core of a star shrinks rapidly and explodes violently under its own weight. When all the substances in the core become neutrons, the contraction process stops immediately and is compressed into a dense planet. But in the case of a black hole, because the mass of the star core is so great that the contraction process goes on endlessly, the neutron itself is ground into powder under the attraction of the squeezing gravity itself, and the rest is the matter with unimaginable density. Anything near it will be sucked in, and the black hole will become like a vacuum cleaner.

It can also be simply understood as: usually, a star only contains hydrogen at first, and hydrogen atoms inside the star collide with each other at all times, resulting in fission and fusion. Because of the huge mass of stars, the energy generated by fission and fusion competes with the gravity of stars to maintain the stability of star structure. As a result of fission and fusion, the internal structure of the hydrogen atom finally changed, broke and formed a new element-helium. Then, helium atoms also participate in fission and fusion, changing the structure and generating lithium. By analogy, beryllium, boron, carbon and nitrogen will be generated in turn according to the order of the periodic table of elements. Stars will collapse until iron is produced. This is because iron is quite stable and can't participate in fission or fusion, and iron exists in stars, which causes the energy in stars to be insufficient to compete with the gravity of massive stars, which leads to the collapse of stars and eventually the formation of black holes.

Like white dwarfs and neutron stars, black holes probably evolved from stars with a mass more than 20 times that of the sun.

When a star ages, its thermonuclear reaction has exhausted the fuel (hydrogen) in the center, and the energy generated by the center is running out. In this way, it no longer has enough strength to bear the huge weight of the shell. Therefore, under the heavy pressure of the shell, the core began to collapse, until finally a small and dense star was formed, which could balance the pressure again.

Stars with smaller mass mainly evolve into white dwarfs, while stars with larger mass may form neutron stars. According to scientists' calculations, the total mass of neutron stars cannot be more than three times that of the sun. If it exceeds this value, there will be no force to compete with its own gravity, which will lead to another big collapse.

This time, according to scientists' guesses, matter will move relentlessly towards the center point until it becomes a small volume and tends to be very dense. When its radius shrinks to a certain extent (it must be smaller than that of schwarzschild radius), as we mentioned above, the huge gravity makes it impossible to shoot out even light, thus cutting off all the connections between the star and the outside world-a "black hole" is born.

According to scientists' calculations, if the speed of an object is 7.9 kilometers per second, it can circle the earth in the air without being pulled back to the ground by the gravity of the earth. This speed is called the first cosmic speed. If you want to get rid of the bondage of the earth's gravity completely, you must have at least a speed of 1 1.2km/s, which is the so-called second cosmic speed. But for other celestial bodies, the speed needed to escape from its surface is not necessarily so great. The greater the mass and the smaller the radius of a celestial body, the harder it is to get rid of its gravity, and the greater the speed required to get rid of it.

According to this truth, we can think that there may be a celestial body with a large mass and a small radius, which makes it escape at the speed of light. In other words, the gravity of this celestial body is so strong that even the light of 300,000 kilometers per second is held by its gravity and cannot run out. Since the light of this celestial body can't escape, we can't see it when we speak, so it is black. Light is the fastest in the universe, and nothing can move faster than the speed of light. Since light can't escape from this celestial body, of course, other substances can't escape. As long as everything is sucked in, it will never come out, just like falling into a bottomless pit. This is a celestial body and people call it a black hole.

We know that the radius of the sun is 700,000 kilometers now. If it becomes a black hole, the radius will be greatly reduced. To what extent? It can only be three kilometers. The earth is more pitiful. Its radius has now exceeded 6000 kilometers. If it becomes a black hole, the radius will be reduced to only a few millimeters. There will be such a big compressor, which can shrink the sun and the earth so much! It's like a fairy tale in a movie, a black hole, so bizarre. However, the above is not imaginary, but based on strict scientific theory. It turns out that black holes are also transformed from stars in their later years, like relatively small stars, which will become white dwarfs in their later years; Neutron stars will form when the mass is relatively large. Now let's add that stars with greater mass will eventually become black holes in their later years. Therefore, to sum up, white dwarf neutron stars and black holes are the results of three changes in the stars in their later years.

Now, the white dwarf is found, the neutron star is found, and the black hole is found? We should also find them. Mainly because black holes are black and really hard to find. Especially those single black holes, there is nothing we can do now. There is a situation where it is easier to find black holes, that is, black holes in binary stars.

A binary star is two stars orbiting each other. Although we can't see the black hole, we can analyze the movement route of the visible stars. What is the reason? Because every star in a binary star moves along an elliptical path, but a single star does not move like this. If we see a star moving along an elliptical route in the sky, but we can't see its companion, it is worth studying carefully. We can measure the size of the ellipse that a star walks through and the time it takes to complete a week. With these, we can calculate the mass of the invisible' companion'. If the calculated mass is very large, which exceeds the mass that a neutron star can have, it can be further proved that it is a black hole.

In Cygnus, there is a pair of binary stars named Cygnus X- 1. One of these binary stars is a visible bright star, but the other is invisible. According to the movement route of the bright star, it can be inferred that its' companion star' mass is very large, at least five times that of the sun. Such a large mass is impossible for any neutron star. Of course, there are other evidences besides these. Therefore, it can be basically determined that the invisible celestial body in Cygnus X- 1 is a black hole. This is the first black hole discovered by human beings.

In addition, several pairs of binary stars are similar to Cygnus X- 1, and there may be black holes in them. Scientists are doing further research on them. It is easy to imagine a "black hole" as a "big black hole", but it is not. The so-called "black hole" is such a celestial body: its gravitational field is so strong that even light cannot escape.