I'm trying to understand the process that destroys particles very shortly after they "appear". I have read that they are usually annihilated by a virtual antiparticle, much in the same way as can happen to real particles. However, is this always the case? And if so, is it an intrinsic property of these particles to appear in pairs and why exactly is this? In other words: could a virtual (anti)particle be created on its "own", without a partner, for example because of the Heisenberg time-energy uncertainty relation, simply because it exists too briefly for it to have any real energy? Apparently, a virtual pair can be split up (Hawking radiation), but can they also be created that way?