A singularity is a rip in space-time, and this “rip” is the very center point of a black hole. This point is so small that it actually has no volume. If we define size in terms of volume, or the amount of space occupied, singularities don’t vary in size, because all of them contain no volume.
Although singularities don’t contain any volume, they contain all the mass of the black hole. If we do a quick math calculation, in which we use the fact that density = (mass) / (volume), we find that black holes have infinite density.
If someone were to throw you into a black hole, you would first pass the event horizon: the point of no return, the point where the gravity of the singularity doesn’t allow anything to escape. Assuming you’re going in feet-first, your feet and legs, hitting the horizon first and being pulled into the singularity, would be stretched and stretched. The rest of your body would follow suit, and you would turn into something akin to spaghetti. The official term for this process is “spaghettification”— we kid you not. You would probably already be dead at this point, but if you weren’t, you would get to experience falling into the singularity and getting all your mass squeezed into a space with no volume. The singularity would assimilate your mass and you would become part of it.
Now, the size of the black hole itself is quantified by the radius, or distance from the singularity to the event horizon. This distance can range from a tenth of a millimeter to more than 400 times the distance between the Earth and the Sun. Keep in mind that light, the fastest thing in the universe, takes 8 minutes to make that journey from the Sun to the Earth.
Generally speaking, the radius of the black hole is correlated to the mass of its singularity. The mass of a singularity can vary from the mass of the moon to the mass of our sun, multiplied by 10 to the 10th power. We refer to the black holes at the top of this range as supermassive black holes, and their mass usually lies between 198,900,000,000,000,000,000,000,000,000,000,000 and 19,890,000,000,000,000,000,000,000,000,000,000,000,000 kilogrammes. In fact, these numbers are so large that there is actually no standard unit prefix for this amount of mass.
To read more, check out this article about the different sizes and types of black holes.
Answered by Deiter H., Expert Leader.
Edited by Jamie V.