Do Black Holes Deteriorate?

There is a theoretical evaporation mechanism called Hawking Radiation that is a quantum mechanical process that allows radiation to be emitted from just at the event horizon of a BH. The simple picture is that quantum fluctuations constantly cause particle-antiparticle pairs to be created now normally these particles immediately annihilate with each other, refunding the energy used to create them. If the pair is created right at the event horizon, one of the pair can be just trapped by the BH's gravity while the other is free to escape. Since the escaping particle requires energy to do so energy balance dictates that the trapped particle has negative energy meaning the black hole loses some of it's mass, if it loses all of it's mass via this mechanism this way then it will no longer exist.

This process is proposed to be ongoing on all black holes but, due to the evaporation timescale scaling with M3 , it is only relevant for fairly small black holes. Tiny tiny black holes will evaporate very rapidly whereas stellar mass black holes will last for time scales comparable to the current age of the universe (even larger black holes will last for 1060 times longer than the universe has existed).

For a black hole to dissipate completely it needs to be radiating away energy per second in Hawking radiation than the energy that is falling in per second. Due to the energy content of mass being quite high, any black hole that is doing accretion will likely be growing faster than HR can shrink it. In fact, due to the ubiquitous presence of the cosmic microwave background providing photons to fall into a black hole wherever it is this means there is a maximum size of BH that will ever dissipate (around the mass of the moon).

Attempts to detect primordial black holes that have since evaporated are ongoing.

The mechanism that produces this Hawking radiation is still not fully understood, no one really knows how to marry the theory with some other qm ideas (like the information paradox), and it has never been observed. Analogues, in quantum optics experiments, have been reported as detected but they are controversial.