The greedy black hole was originally a star.

In fact, the concept of black hole has been put forward for more than 200 years. In 1783, John Michel, the British Job, first proposed the existence of a star that is large enough and compact enough. The gravity of Michel is so strong that even light cannot escape. A few years later, Pierre Simon de Laplace, a French scientist, put forward a similar view with Michel in his book "world system". But interestingly enough, the third and later versions of the book never mentioned it again. Maybe he thought the idea was too absurd. More than a century later, the German astronomer Karl Schwasi (Karl Schwarzschild) solved the first rigorous solution of Einstein's general relativistic equation in 1916. This solution indicates that there may exist a large class of celestial bodies, known as "black holes" after 60s. The first time we saw the black hole was in 1971. At that time, we discovered a strong X ray pulse source from the Swan region by the Uhuru, a small astronomical satellite launched in December 12, 1970. It was named the Swan X L, which is the first black hole confirmed by the body. Since then, black holes have become a hot topic in astrophysics.Today, we have learned a lot about the formation process of black holes. Simply speaking, black holes are massive stars that collapse after supernova explosion, that is, their very strong contraction.We can think of a black hole as a huge "Grinder" that pulverized the incoming material. Its center is known as the "grinding point", the so-called "singularity". In this "singularity", the laws of science and our ability to predict the future have failed. The boundary of a black hole is called the "Horizon". This is an interface with no return. As long as it crosses this interface, it falls into the interior of the black hole. But assuming that someone unfortunately falls into it, the first thing he sees is the light captured by the black hole, and these rays spiral into the gravitational vortex.

Giant stars collapse to form black holes

After a steady youth and middle age, a star will enter the old age and eventually die. The star, which is at least 10 times larger than the sun, will expand in old age and become a red giant, and then explode - supernova explosion. The outer layer of material is thrown into space, and the core of the center collapses suddenly and violently under the action of gravity, forming a black hole.

Space and time distorted by black holes

According to Einstein's general theory of relativity, when there is no gravity effect, time and space (grid in Figure) is flat (see left), but when there is gravity, time and space will be bent (see chart).The right side of the diagram shows a serious distortion of the space-time around the black hole due to the strong gravitational attraction of the black hole. A black hole with the same mass as the sun has a radius of only 3 kilometers, while the sun's radius is 696 thousand kilometers.