Black holes emit radition called : “virtual particles.”
These particles do not obey the regular laws of physics. They can be created in pairs out of nothing, contrary to the normal laws of physics. As pairs, they can then collide with one another and be destroyed back into empty space. Normally, we would therefore never even see these particles before they disappear.
Hawking theorized that if a pair were created right at the event horizon of the black hole, then one particle of the pair could be sucked into the hole while the other escaped outward.
The result to an outside observer would be to see a new particle arrive that appears to be coming from the black hole. Hawking proposed that the resulting stream of these particles, which were photons, would then look like radiation coming from the black hole, an effect that came to be called “Hawking radiation.”
So in fact, black holes, which were thought to emit no radiation all (which is why they are called “black” holes), in actuality give off a small amount of light! In Hawking’s words, “Black holes ain’t so black!”