A question related to black holes Not a physicist just a simple guy, don't know much about physics as well. Just like to read things. I was reading about black holes and a question popped in my mind. 

If I understand it correctly then the black hole is created by collapse of a super massive star at the end of its life. This star will have a finite mass. Then what leads to the black hole to have such massive gravity so that nothing can escape it (because if it was a star before with a finite mass then it would also have some finite gravity, right)?  

And then they start absorbing more and more matter. So they grow bigger and bigger. Do black holes die? 

Do all galaxies have a black hole at their center?

Thanks &amp; Regards

Update-1

Found answer to the question, do black holes die?

Update-2

Found answer to the question, Do all galaxies have black hole in the center?

Posting the answer link here so anyone having this questions can find all answers in one place.
Answering your first question:


  If I understand it correctly then the black hole is created by
  collapse of a super massive star at the end of its life. This star
  will have a finite mass. Then what leads to the black hole to have
  such massive gravity so that nothing can escape it (because if it was
  a star before with a finite mass then it would also have some finite
  gravity, right)?


You are right that a black hole will have a finite mass that is smaller than that of the massive star that collapsed (some matter is carried off by the supernova). At large distances the gravitational field of this black hole will be no different than that of a star with the same mass.

The difference arises because in a black hole this mass is compressed into a much smaller volume. Consequently, you can get much closer to the concentration of mass, than you would be able to for a star (where the mass is scattered over a relatively large volume). It is here where the gravitational fields can become really "strong" and prevent light from escaping.