If stars and planets can perish. can black holes also perish?

The only known mechanism by which a black hole can lose mass is so-called Hawking radiation. It’s a quantum effect. According to quantum theory, a particle-antiparticle can form in empty space for a short time, which then quickly recombine and disappear again. If that formation happens close to a black hole, it may happen that one of the two particles is absorbed and the other is not; the latter can then no longer disappear, and a little mass has been added outside the black hole, so the black hole has lost some mass.

It turns out that the smaller a black hole, the more important the role of Hawking radiation. This can therefore only be of significance for microscopic black holes. For the large black holes found in the centers of galaxies and the moderately large ones in binary stars, the phenomenon lasts orders of magnitude longer than the age of the universe.

Another, more spectacular, way for a black hole to “disappear” is to be eaten by another black hole. Then of course you end up with a black hole, which is bigger. In some galaxies we see that there are two black holes; often (always?) it is then two galaxies – each with a black hole in their center – that are merging, and someday those black holes will also merge.