## If black holes suck it all up, what do they do with it?

Black holes remain mysterious objects that fascinate both the general public and scientists. Many of the unanswered questions in modern physics are about them. But the question you ask is based on a wrong idea, a black hole is not a vacuum cleaner, it is not exactly that it absorbs everything. We are going to explain it little by little because, when we get close to a black hole, the laws of physics are very extreme.

To understand what happens around one of them you need to know what the event horizon is. This is a theoretical limit, it is not an area of space where you can point a finger and say “that’s there.” It is a boundary that is defined as the last orbit in which an electromagnetic wave traveling at the speed of light can reach us.

Let’s see it with an example. If we throw an apple towards the sky, it falls back towards us due to the force of gravity of the Earth. But if we were superheroes and we could throw the apple with a lot of speed, above 11 kilometers per second (the escape speed of the Earth), the apple would reach space and escape the gravity of our planet. A black hole has a much stronger gravitational field than Earth’s, so near it you need a much higher speed to escape its force of gravity. So much so that, when we are close to one of them, the speed needed to escape its gravity is higher than the speed of light. But here a problem arises because, according to the theory of relativity, there is a limit, which is the speed of light.

With the laws of physics that we currently know, there is nothing that goes faster than the speed of light.

In the event horizon, the escape velocity is equal to the speed of light, that is, an electromagnetic wave that goes at the speed of light a little outside the event horizon can reach us, but a little by within the event horizon it can no longer reach us because it cannot travel faster than light. So when we think of an object near a black hole, it is not that it absorbs it, but that once the event horizon is crossed, the particles would continue to circle around it because to escape they would have to go faster than light.

If we could follow the path of an object that crossed the event horizon and approached a black hole, we would get the last information that can travel at the speed of light (that is, right on the event horizon), and it would be like an image stopped forever.

If we were to launch a spacecraft into a black hole, what we would observe is that the closer it got to the event horizon we would see it move in slow motion and when it reached the event horizon we would see it standing still. But if we were inside the ship, for us the time would remain the same, we would approach the black hole, we would cross the event horizon and we would continue to circle the black hole. But if we were on the ship and we wanted to call our family at home, once we crossed the event horizon we could not do so because our information could not travel faster than light. What happens once the event horizon is crossed remains within the event horizon, disconnected from what is outside.

The phrase that is heard whenever it says that nothing can escape from a black hole does not mean that the hole absorbs it, what it means is that it somehow traps it and causes it to rotate around it in extreme orbits within the horizon of events. Now yes, the ship would not remain the same. The effects of gravity would be so strong that it would become a kind of spaghetti due to a process called precisely spaghetti.

It means that since gravity is a function of the square of the distance and in black holes it is so huge, small variations in distance change the intensity of the gravitational field. For example, beyond the event horizon, gravity would act differently on my head than on my feet because the meter and a bit between them is already a distance that makes it different in those two points.