Black Holes Explained – From Birth to Death

Black holes are one of the strangest things in the universe. They seem to have no meaning; where do they come from ? And what happens if you fall into it Stars are an incredibly massive collection of hydrogen atoms which collapse into huge clouds of gas due to their own gravity. In their hearts, nuclear fusions crush hydrogen atoms by transforming them into helium, Releasing an astronomical amount of energy. This energy, which is in the form of radiation, opposes gravity, Now a delicate balance between the two forces.

As long as there is a fusion at the level of the heart, the star remains fairly stable. But for stars much more massive than our Sun the temperature and pressure in the core allows them to merge the heavier elements, till you reach the iron. Unlike the previous elements, the melting process creating iron does not generate energy. Iron accumulates in the center of the star until it reaches a critical quantity, and the balance between radiation and gravity is suddenly broken. The nucleus collapses In a fraction of a second, the star implodes, at a quarter of the speed of light concentrating even more mass in its core that is the time all the heaviest elements are created, while the star dies in an explosion, the supernova.

Photo by Rakicevic Nenad from Pexels

 This produces a neutron star or, if the star is large enough, the whole mass of the nucleus collapses into a black hole. If you were to look at a black hole, what you would really see is the event horizon. Everything that crosses the horizon of events must travel needs faster than the speed of light to escape it. In other words, it is impossible. So we only see a black sphere reflecting nothing.

If the horizon of events is "black", what is the "hole" of the black hole? 

The singularity. We don't know exactly what it is. A singularity could be something infinitely dense, i.e. its entire mass is concentrated in a single point of space, without surface or volume. Or something completely different. Currently we do not know. It's like dividing by zero. By the way, black holes don't vacuum things like a vacuum cleaner. If we exchanged the Sun for a black hole of equivalent mass nothing would change for Earth, except that we would die of cold, obviously.

What would happen if you fell into a black hole? 

The experience of time is different around black holes. From the outside, you seem to slow down as you approach the horizon of events, so time passes more slowly for you.After a while, you would seem to freeze in time, slowly turn red, and disappear. While from your perspective, you could see the rest of the universe fast forward, as if you see in the future. At the moment, we don't know what happens next, but there are two possibilities.

One: you will die a quick death. 

A black hole bends so much space that once the horizon of events crosses there is only one possible direction. You can take it literally: inside the event horizon you can only go in one direction. It's like being in a very narrow alley that closes behind you after each step.The mass of the black hole is so concentrated, that at some point even small distances of a few centimeters would mean that gravity acts with millions of times more force on different parts of your body. Your cells tear apart as your body stretches more and more, until you are just a stream of plasma an atom thick.

Two: you will die a very quick death. 

Right after hitting the horizon of events, you would crash into a wall of fire and you would be finished in an instant. None of these options are very pleasant. When you die depends on the mass of the black hole. A smaller black hole would kill you before you entered its event horizon, when you could travel in a supermassive black hole for a certain time. In principle, the further away you are from the singularity, the farther you live. Black holes are available in different sizes. There are the black holes of solar mass sometimes making the mass of the Sun and the diameter of an asteroid. And there are the supermassive black holes, which are at the heart of each galaxy and which have been feeding for billions of years.

Currently, the largest known supermassive black hole is S5 0014 + 81, 40 billion times the mass of our Sun. It is 236.7 billion km in diameter, which is 47 times the Sun-Pluto distance. As powerful as they are, black holes will eventually evaporate in a process called Hawking radiation. To understand how it works, we need to look at the empty space. The empty space is not really empty, but filled with virtual particles appearing and annihilating each other then. When it happens right on the edge of the black hole, one of the particles will be pulled into the black hole and the other will escape and become a real particle.

So the black hole loses energy. It happens incredibly slowly at first, and it gets faster when the black hole gets smaller. When it comes to the mass size of a large asteroid, it radiates at room temperature. When it has the mass of a mountain, it radiates at about the temperature of our Sun. And in the last second of his life, the black hole radiates with the energy of billions of bombs nuclear in a huge explosion. But this process is incredibly slow. The biggest black hole we know should take a bunch of years to evaporate. It's so long that when the last black hole will evaporate, no one will be there to witness it. The universe will have become uninhabitable long before. 

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