How are blackholes created?
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Cold stars collapsing under the gravity of their mass, with no nuclear fusion going on there is no heat being generated to keep the atoms apart, so the star becomes denser and denser until a black hole is formed. https://youtu.be/Y5XzPOrItaI
When you’re at the Earth’s surface, it’s really hard to fly straight up. If you get further up, it becomes easier and easier to fly away because you’re further away from all of Earth’s mass and the pull of gravity is weaker.
It’s possible to imagine Earth being so dense and heavy that a rocket on its surface couldn’t take off, no matter how powerful its engines were. Eventually, there could be an object so heavy that even light, or other things moving at the speed of light, can’t get away.
That’s what a black hole is. Something so dense that, once you get close enough, the gravity is enough that even light cannot escape.
To make one, you’d have to smash some amount of matter together so hard that that radius of inescapability is bigger than the radius of the matter itself. In nature, that might be when an already ultra-dense neutron star hits something else, or maybe when a star collapses after a supernova. At CERN, it’s *possible*, but not yet demonstrated, that we could slam two particles into each other hard enough to make a black hole smaller than an atom.
There are multiple types of black holes, and the others explaining stars collapsing is correct, but I would add the reason why they collapse. Stars generate heat with nuclear fusion. They squeeze atoms together so hard, they merge and become a bigger atom. The most basic example is squeezing hydrogen until it becomes helium. This continues with heavier elements, but iron can’t be fused any further, so once the star’s core contains mostly iron, it stops producing heat. This heat is what keeps the star “inflated”, preventing gravity from pulling everything into the center. Once it’s gone, gravity wins, most of the star falls into the center while the outermost layers break free. The core and inner layers collapse into a heavy object (white dwarf stars are the least dense, neutron stars are in-between, black holes are the densest) while the rest of the star turns into a supernova explosion.
The other type of black hole, a primordial one, is harder to detect for a few reasons. They are very small and they were not created by collapsing stars but by the big bang itself, so they don’t come with the usual gas clouds left by exploding stars. Their existence is debated, but there is even a theory stating that there is one in our solar system. There is a missing planet that has more mass than Earth based on the effects it has on objects in the outer solar system, but it hasn’t been found yet, even though its effects show where it’s supposed to be
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.
Imagine taking something really, really big and then squishing it into something really, really small.
A star is essentially a gigantic, perpetual balancing act. On the one side, you have gravity trying to squish all of the gas atoms, which makes up the star, closer and closer together. On the other side, you have fusion (smooshing the atoms together because there’s a gazillion tons of other atoms dog piling on top of them) happening in the core of the star which releases incredible amounts of energy and tries to push the star apart.
So gravity pushes everything in, fusion pushes everything out, and the balancing act between them is a star. But, because stars are made out of a finite amount of material, eventually over time the balance gets broken. Gravity wins and the star collapses in on itself. Now you have an entire stars worth of mass that’s been smooshed into an infinitesimally small point. The gravity of all that mass doesn’t go away simply because the volume of the mass is smaller so what your left with is a region of space – a shell which surrounds that infinitesimally small point – where gravity becomes so strong that you would need to exceed the speed of light to escape it.. which is physically impossible. A black hole is formed.
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