About putting forward the history of black holes
John Lin Kewei, a British geographer, first put forward the problem of black holes. 1783, he proposed that if the mass of a celestial body is the same as that of the sun and the diameter of the celestial body is only about 3 kilometers, then the gravity on the surface of this celestial body is so great that even the fastest photon in the universe cannot escape from its surface.
In addition, the French physicist Laplace predicted in 1796: "If the mass of a celestial body is about 250 times that of the sun and its diameter is equivalent to that of the earth, the gravity on the surface of this celestial body will become so great that even light cannot escape." Until Einstein published the general theory of relativity in the 20th century, we had a lot of new knowledge about the theory of black holes, such as the inevitable conditions for the formation of black holes and three unique physical characteristics of black holes.
Research by Lawrence Livermore National Laboratory in the United States pointed out that medium-sized black holes may "resurrect" dead white dwarfs. The picture shows a schematic diagram of the black hole inhaling nearby blue star matter. Overview of black holes
A black hole is a space-time region, and it will show such a strong gravitational effect that no particles and electromagnetic radiation, such as photons, can escape from the inside of the black hole. General relativity predicts that a dense enough mass can bend space-time and form an inescapable regional boundary, which is the so-called event horizon. Simply put, this is the end of the message and you can't convey it.
At present, there is no direct evidence of black holes, but indirect evidence of black holes can be found from the space-time around the black holes. For example, when a black hole affects the surrounding stars, the matter of the stars will fall into the black hole due to the strong gravity of the black hole, and an accretion disk will be formed between the black hole and the stars. In this process, the matter of the star will be heated and radiate energy (X-rays), which will be observed by us. What needs to be known here is that no real black hole has been found at present, only candidates similar to black holes have been found.
Schematic diagram of giant accretion disk in X-ray binary system
The formation of black holes
A black hole is a special celestial body formed by the death of a massive star above the critical value. At first, typical stars, such as the sun, relied on hydrogen fusion to maintain energy. Then the hydrogen ran out, and due to the pressure of gravity, the core environment turned into helium and began to fuse. More massive stars will fuse with heavier elements until they reach iron. According to the theory, if the core mass of a star is greater than or equal to 3.2 times the mass of the sun, then there is no energy (repulsion) to resist its own gravity, and gravity begins to collapse infinitely toward the center, and then a "black hole" is formed, and the center of the black hole will tend to be singular.
At present, there are two classical limits for the formation of black holes. The first is the Oppenheimer-volkov limit (the upper mass limit of a cold neutron star), which is close to 2. 17 times the mass of the sun. If a cold neutron star exceeds this limit, it is likely to collapse into a black hole due to strong gravity. The second is the famous schwarzschild radius, and schwarzschild radius means that when an object is compressed to a critical radius, it will form a black hole. Strictly speaking, it is the gravity field value of a spherically symmetric, non-rotating and uncharged object. When an object of a specific mass is compressed to this value, its own gravity can be compressed to a singularity without constraint. Theoretically, the schwarzschild radius of the sun is about 3 kilometers, and the schwarzschild radius of the earth is only about 9 millimeters. A celestial body with a mass greater than or equal to 3.2 times that of the sun will form a black hole if it is compressed into its schwarzschild radius.