Black holes are really fascinating stuff. Thanks to Stephen Hawking, George Ellis and Roger Penrose they went from being a real mystery to becoming something we think we know quite well today. With this I do not mean that we have discovered all their secrets, but it is true that we at least have a fairly complete idea of what they are and how they behave.
In general terms, the most widespread and accepted definition says that black holes are finite regions of space that have, inside, such an enormous concentration of mass that they generate a massive gravitational field, to such an extent that they generate such an attraction effect. intense that not even light can escape from it.
According to Stephen Hawking, they emit a specific type of radiation , although it seems that in some cases the radiation does not come from the black hole itself, but rather from its accretion disk , a disk-shaped structure that is usually made of gas and dust and that revolves around the black hole.
The enormous gravity that a black hole has causes a singularity surrounded by a closed surface known as the event horizon, separates the region of the black hole from the rest of the universe, and causes the curvature of spacetime. As we have said, once something enters that event horizon, it can no longer escape it.
We also know that today there are different types of black holes that are classified based on their mass, and also other aspects such as their charge and angular momentum. If we talk about size, the differences between these types of black holes are also enormous , and to demonstrate this , NASA has shared a very interesting video where they show us, in a comparative way, the size of the smallest and largest black holes that we know of.
We start with our Sun as a reference point, and from there the video scales based on the size of each of those black holes. As you can, the latter are so huge that I think the super massive concept is too small for them, since TON 618 has a mass equivalent to 66,000 million suns.