When I was a kid, I struggled to understand the meaning of a “black hole”. I was baffled how an object can suck in everything around it and never be full. In elementary school, my science teacher told us that “your chair were to contract indefinitely, it will become a black hole that will be so small that you will not even be able to see it; however, it will continue to attract everything into itself – including you, who is sitting on that chair right now – forever.
A black hole is the leftover of a high-mass dead star. For a low-mass star (like our Sun), after its death, it will contract until its core is completely made of carbon, at which point the heat will never be high enough to perform fusion, and the dead body of the star – a sphere of carbon – is called a white dwarf. A medium mass star will become a neutron star on its death. However, for an extremely high mass star, its gravitational collapse will become so strong that it will cause a glorious explosion – supernova – and the leftover core will be indefinitely massive – so massive that all the mass will gather in a point (singularity) and its gravitational force will suck in everything around it. The radius in which every matter including light will be sucked in is called the Schwarzschild Radius, where the escape velocity is the speed of light. In other words, everything that has a speed smaller than or equal to the speed of light will not be able to escape the black hole.
Thus, what my teacher told us in elementary school is somewhat correct. Even though the original mass of the chair is so small that it would only create a Schwarzschild radius of little more than 0, it will still be able to consume whatever is within that radius.
