In an approach to classical physics, black holes are very large celestial objects - some hundreds of times the mass of the Sun - that occupy a very small space.
Its gravitational field is so intense that not even the speed of light is greater than its escape velocity.
With this, the light that enters a black hole can no longer come out, so that it cannot be observed by the usual techniques that analyze the light emitted or reflected by celestial objects.
And what is escape velocity?
We call escape velocity one whose intensity is sufficient for an object to “escape” from the action of the gravitational field. The escape velocity on the earth's surface is approximately 11.2 km / s; In order for an object to break free from the gravity of our planet, it must be launched faster than it.
If a black hole cannot be seen, how is it detected?
The observation of a black hole happens indirectly, because what can be seen are the effects that it has on nearby regions. Due to its huge gravitational field, other bodies tend to be attracted to it. By measuring how fast objects move toward you in neighboring regions, you can discover their mass.
When a black hole absorbs matter from nearby bodies, it gets compressed, heats up significantly, and emits large amounts of X-ray radiation. The first detections of the black holes were made with sensors that captured this X-ray emission.
Strong evidence has already been observed that there are supermassive black holes in the center of some spiral galaxies, including some scientists believe that there is one of these black holes in the center of our galaxy, the Milky Way.