How are blackholes created?
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Depends on the black hole. We know of the existence of two kinds of black holes, stellar mass black holes (black holes around the size of our sun), and supermassive black holes (black holes hundreds of thousands or millions of times bigger than the sun). We hypothesize the existence of a third kind of black hole, micro black holes (black holes significantly smaller than the sun), but haven’t shown they exist yet.
All three kinds are created through functionally the same process. So much matter and energy is crammed into such a small space that the force of gravity within a small region becomes so strong that no known force in the universe can stop things from collapsing together under the gravitational pull. This leaves behind an object that we know little about (often called a singularity) because all of our math breaks down when trying to describe it. At a certain distance from the singularity, there is a region where the force of gravity is so strong that the escape velocity from the singularity becomes equal to the speed of light. This is the event horizon (the black sphere around the singularity). The event horizon isn’t an actual object, though. It’s just a limit where gravity becomes too strong for anything to escape the black hole, i.e., you couldn’t “touch” the event horizon. It’s sort of similar to a rainbow. It’s not an actual object, more of a *perceived* object caused by special conditions.
So, all black holes are essentially the same. The differences come in how the three kinds of black holes I mentioned are created. Stellar mass black holes are the ones we know the most about. These come into existence a few ways. The most well known is through the death of a very large star. When really large stars die, their cores stop producing energy (practically instantly, it’s not a slow process) this means there’s nothing to hold the rest of the star up and the core collapses on itself (in about 1/4 of a second). This squishes so much material together that it creates a black hole since so much material is so close together that gravity becomes really strong. You can also create stellar mass black holes when stars (particularly neutron stars) collide and smash their material together.
The other two kinds of black holes we don’t know as much about. However, we at least know that supermassive black holes exist. They are at the center of most galaxies, including ours. That said, we aren’t sure how they came to be. Some of the leading hypotheses suggest that they formed similarly to stellar mass black holes but very early in the universe’s existence and have just been growing over time as they eat more things, including other black holes. Other hypotheses suggest that the early universe was much different than the universe today and allowed the formation of supermassive stars, which, when they died, would create the supermassive black holes.
Micro black holes, on the other hand, are purely hypothetical. We don’t know if they exist or not (that said, nothing would necessarily prevent them from existing. Black holes can be any size). Also, the possible mechanisms for their creation aren’t fully fleshed out yet and have a lot of quantum mechanics involved in their study, which is too much for ELI5 (and me). Fortunately, if micro black holes exist, they should actually be relatively easy to find. All black holes emit radiation through a process called “Hawking radiation,” and counterintuitively, the smaller a black hole is, the more Hawking radiation it releases. Micro black holes should release enough to be possible to see (if they exist), and if they are *really* small, they should essentially explode as they release all their trapped mass rapidly through Hawking radiation. This would be able to be seen from many thousands of light years away, and we are looking for them.
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