Can black holes die? if not, then is it possible for black holes to continue merging and expanding until all matter in the universe is pulled into one big massive black hole? if black holes can die then what happens with the matter that has been pulled in by the gravitational force? would a white hole then be produced after the black hole dies?
Black holes can, in fact, die! The way they die, however, is theoretical and not proven, but it’s possible and it’s called Hawking radiation. To summarize // oversimplify (because it’s really complicated), according to quantum physics we know that particle-antiparticle pairs pop in and out of existence all the time, and usually annihilate each other almost immediately. They are able to come into existence by “borrowing” energy from the universe, and when they annihilate they “return” that energy back.
Now, what if a particle-antiparticle pair comes into being right at the edge of a black hole’s event horizon, and one particle falls in and the other escapes? Well, now you’ve just “created” one particle that’s entered the universe, and one particle that’s entered the black hole (and can’t escape). Since these two particles can’t annihilate, they can’t “return” their borrowed energy to the universe. However, you can’t just spontaneously create energy; it has to come from somewhere. That somewhere is, you guessed it, the black hole. So, the amount of energy in the black hole decreases by the amount of energy required to create the particle-antiparticle pair. Since mass and energy are equivalent (e=mc2), the mass of the black hole decreases ever so slightly - the mass of an electron, positron, or other subatomic particle.
This process takes billions of years, and it will be another several billion years before we’re able to see black holes finish evaporating. This process is expected to be faster the smaller the black hole is - once a black hole is small enough, this process happens faster and faster, until the black hole gives off lots and lots of radiation and “explodes” (think: gamma rays, really bright, as bright or brighter than a supernova), and no longer exists. While this isn’t proven and is entirely theoretical, it’s pretty cool that black holes, the killers of the universe from which nothing should be able to escape, are slowly losing mass over billions and trillions of years, one subatomic mass at a time.