Time and space are the stage of various physical phenomena. However, this stage is not incomparably hard. The big guys in the universe may trample on this stage.
In order to show the elasticity of the space-time stage, we can imagine the space section in space-time as a rubber film. All kinds of objects in the universe, such as the earth and the moon, are dancers stepping on a rubber film. After the earth came on stage, he stepped on the rubber film and sank it. Therefore, the moon next to the earth needs to rotate around the earth and use centrifugal force to ensure that it does not fall to the ground. At the same time, in order to launch a spacecraft from the earth, the spacecraft also has to spend a lot of effort to climb out of this depressed area in order to swim freely in space.
But the earth is really a lightweight player in the universe. Imagine a guy as big as the earth, but the density is 800 million times that of the earth. As soon as such actors come on stage, they will step through a hole in the rubber film stage and fall into the hole with a plop. We call this hole a black hole.
Standing on the earth far away from the black hole, we will find that the black hole steps on the rubber film so curved that no matter how fast the spacecraft is launched, it cannot escape from the edge of the black hole. Even the fastest light in the universe cannot escape from a black hole. Since light cannot escape, black holes look as if they are black. This is the origin of the name of black hole.
Readers may wonder, since the black hole has trampled on the rubber film of space-time, what does the broken area look like? Is there space-time in the black hole? No one can look into the black hole and come out to tell us the answer to this question. However, according to theoretical speculation, there is space-time in black holes. Nature automatically patched the broken rubber film. However, I don't know whether nature is careless or intentional. She "wrong" the direction of this patch, so that the time direction inside the black hole is our space direction (along the radius of the black hole), and the space direction from the center of the black hole to the surface in our eyes becomes the time direction inside the black hole.
Because the time and space inside the black hole have changed their positions, the center of the black hole we outsiders think is actually the future in the patch space-time inside the black hole. Therefore, all objects in the black hole, no matter how they think of "running out", will inevitably fall into the center of the black hole, because this is their future. In this way, a large amount of matter accumulates in the center of the black hole, and the density exceeds the density that can be described by known physical laws. What happens at the center of this black hole is still a mystery to us.