Every galaxy that is Milky-Way sized should have hundreds of millions of black holes, created mostly from the deaths of most stars. At the centers of these galaxies, massive black holes have devoured enough matter to grow to millions or even billions of times the Sun's mass, where sometimes they are caught in the act of feeding on the matter, removing radiation and relativistic jets in the process. But, any in-falling mass would look like it would take an infinite time to fall in, does that prevent black holes from growing?
It sounds like a paradox, but this explains how it all happens. When you think about a black hole, there are two different ways that you can do it. The first way is to consider it from the point of view of outside, external observer. You can picture a black hole the way scientists would see it. From this perspective, a black hole is simply a region of space where enough mass is contained within a given volume that the escape velocity exceeds the speed of light.To read more, click here.