• Question: One of Stephen Hawkins many achievements was that he proved radiation can be detected coming out of black holes. Since radiation is a form of energy and it is supposed nothing escapes black holes, where is this radiation energy converted from? From within the black hole itself?

    Asked by on 5 Feb 2017. This question was also asked by .
    • Photo: Craig Fisher

      Craig Fisher answered on 5 Feb 2017:

      “Hawking radiation”, the radiation admitted from a black hole, is actually generated at the very rim (or “event horizon”) of the black hole by the formation of subatomic particles and antiparticles, some of which get sucked into the black hole, and some of which escape. This means the black hole is slowly losing mass (the virtual particles form by “borrowing” from the black hole’s gravitational energy), so if it is not sucking in any other matter it will eventually disappear (which is probably why you don’t see many small black holes floating around the place – they disappear quickly!)

      The radiation is actually a consequence of quantum effects, and strictly speaking “black holes” are not entirely black (more like a “very, very, very dark charcoal”?). The phrase “nothing escapes from a black hole” was coined after Einstein published his general theory of relativity, which doesn’t include any quantum theory. Based on our current understanding, it is more accurate to say “very, very little escapes from black holes!”