So radiation defies the laws of gravity?
No, but thermal radiation coming from black holes apparently defies the laws of quantum mechanics.
Assuming you are referring to Hawking radiation, the theory as I understand it is this:
In a given space there is a non-zero chance of a particle and its antiparticle springing into existence. In most circumstances these immediately annihilate each other and no creation of mass or loss of energy occurs.
However at the event horizon, the boundary between what fall in and what can escape the black hole, one of those particles may escape while the other falls in. The escaping particles are the source of Hawking Radiation. If the black hole generates these particles at a faster rate than it is absorbing mass then it will slowly evaporate.