My understanding of hawking radiation is that the radiation it emits is from virtual particles the pop in and out of existence on the event horizon. To satisfy the law of conservation of mass, one particle has a + mass and one has a - mass. Most of these particles cancel each other out almost instantly, but sometimes a particle will fall in past the event horizon while its counterpart is free to escape. I believe that the negative particle is generally the one to fall in which is what allows black holes to eventually evaporate.