Question: How do the black holes live and die?

Nicolas Labrosse answered on 21 Jun 2017:

OK, that’s a tricky question, Polina, but I know you like black holes, so I’ll try to give you some information. However, I’m not an expert so I can’t promise to give you the full picture.
There are several types of black holes, and they can be distinguished according to their mass.
There are primordial black holes which appeared soon after the Big Bang, and those I don’t know enough about. They are not very massive.
There are stellar mass black holes, which I’ll talk to you about soon.
There are massive black holes, with a mass of several tens of a star like the Sun. We are now sure they exist, because we have detected gravitational waves resulting from collisions between pairs of them. This is a completely new, exciting, great field of research. My colleagues here in Glasgow are heavily involved in the detection of gravitational waves, and in their analysis. While they are confident that these black holes weigh something like 30-50 times the mass of the Sun, no one knows for sure how they are formed. And what happens to them later.
Finally, the supermassive black holes found at the centre of many galaxies, including our very own galaxy the Milky Way. These black holes weigh thousands to millions times the mass of the Sun. Again, I don’t know enough about them to talk to you in length about them. We are sure they exist, we’ve detected them, but how they are formed and what happens to them later is less clear.

So, the stellar-mass black holes… They form when a very massive star, say about 10 times or more the mass of the Sun, reaches the very end of its life. After it explodes as a supernova, the left over from the core of the star, which will be very dense, will collapse under its own weight as it’s so massive. There is nothing to stop this collapse, and eventually the collapsing core forms a black hole: a very dense thing exerting such a strong, extreme gravitational pull that nothing can escape from it, not even light. That is why it is called like that: it’s black (cannot emit light) and like a hole (with matter around it falling on it). In fact, only the matter that gets very close to it will fall on it. So as time goes, there is less and less material (for example, gas) that will be sufficiently close to the black hole to fall on it. So after such a black hole has formed, it will grow in mass as it continues to attract matter around it, until there is not much left to fall on it. Its mass will then stay roughly constant, and it will remain a black hole for the rest of time.

I hope it makes sense!