WHAT IS A BLACK HOLE?

In a nutshell, black holes are objects that cannot be penetrated by light due to the force of gravity.
For gravity to be so great that even light cannot escape, it is not enough to add the weight or mass of an object, that weight must be confined within a very small range. (Scientifically speaking, weight and mass are not the same thing, but for everyone to understand, I just use the word weight instead of the word mass.)
Thus the schwarzschild radius of an object refers to the small size of an object that must be within its entire weight to be a black hole. It depends on the weight of the object.
The Earth’s schwarzschild radius is 9 mm. 3KM of the Sun.
If we compress our earth in any way and make it a sphere with a radius of only 9 mm, the earth will become a black hole.
When we compress our Earth, which has a mass of 5.972 × 10 ^ 24 kg, and the mountains, rivers, and oceans, by any means, and reduce that weight to the size of a sphere (just 9 mm radius), the Earth becomes a black hole.

It is said to help you understand what a black hole is. We can never compress the earth, so the earth will never become a black hole.
In short, a black hole is unique in that its weight is confined to a very small space, rather than a massive object.
There are a lot of stars heavier than a black hole.
They do not turn into a black hole as long as they are burning. The energy generated in them will resist their gravitational pull. Thus they will continue to expand without shrinking.
But the core of stars that are more than 20 times heavier than our Sun will begin to shrink due to gravitational friction when it runs out of fuel and does not have the energy to stop expanding. If a shrinking core of a star weighs more than 3 times as much as the Sun, no force can stop the contraction of that stellar core. It shrinks due to its own gravitational force, which is smaller than its Schwarzschild radius. That is when black holes appear.
After a star burns like this, there will be an explosion called a supernova before it turns black. In that eruption, other parts of the star will be scattered. After that, the core that shrinks becomes a small black hole.