The black hole

The term "black hole" was coined by the American physicist John Wheeler in 1967 to describe a mass-energy concentration that collapsed gravitationally under its own force of attraction and became so compact that even photons can not escape this gravitational force.
A black hole is a region of space from which nothing can escape, not even light. This can only happen when there is a very large mass sufficiently concentrated, and the gravitational attraction force is sufficient to retain any object, particle or even light ray.

To make a black hole, you need to confine a large mass in a sufficiently small area of ​​space. Take the example of the Sun: it weighs about 2 trillion trillion tons, and its radius is 700 000 km, 200 times that of the Earth. If you managed to concentrate the whole mass of the Sun in a radius of less than 3 kilometers, it would create a black hole: any object or light ray that would approach within 3 kilometers could not escape.

To create a black hole with the Earth, it is even more difficult since it would have to concentrate all its mass in a radius of one centimeter ... and of course that would create a black hole which would be only one centimeter! And yet astrophysicists are now convinced that black holes really exist, and that there is even one very close to home: in the center of our galaxy, the Milky Way.

If you want to see a black hole with your own eyes, come out tonight around midnight and look south. A little above the horizon, you should see the constellation Sagittarius, recognizable by a small pattern well known to amateurs: the teapot. As the picture below shows, the Milky Way passes close to the teapot, and near its beak is the direction that indicates the center of the Milky Way. And there is an object called Sagittarius A *, which we think today is a supergiant black hole, well stalled in the middle of our galaxy!