According to Stephen Hawking, black holes emit electromagnetic radiation(Hawking radiation), won't the EM radiations themselves be sucked back in by the black hole?

I also read on wiki the following:

An important difference between the black hole radiation as computed by Hawking and thermal radiation emitted from a black body is that the latter is statistical in nature, and only its average satisfies what is known as Planck's law of black body radiation, while the former fits the data better. Thus thermal radiation contains information about the body that emitted it, while Hawking radiation seems to contain no such information, and depends only on the mass, angular momentum, and charge of the black hole (the no-hair theorem). This leads to the black hole information paradox.

So if the BH does suck back in the radiation then there would be no way of finding out if it has done so because the information of Hawking radiation is not defined. To counter argue that statement, let's say that Hawking radiation is not sucked back by the BH, then does that mean that information-less systems are not affected by a BH?

Please pardon my ignorance about the topic.

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    $\begingroup$ Do note that Hawking radiation is emitted from outside the event horizon; hence, some of the radiation will be able to escape. $\endgroup$
    – Harsha
    Oct 26, 2016 at 20:19
  • $\begingroup$ @Harsha yes I am aware of that but my very problem is that statement of H.radiation is emitted from outside the event horizon. If this is so why won't the black hole suck back the radiation emitted? It is well within the vicinity of the BH. This brings another question: if Hawking radiation is not sucked by the BH does that mean that information-less systems are not affected by a BH? $\endgroup$ Oct 27, 2016 at 3:26
  • $\begingroup$ @Naveel If light is emitted in a direction away from the black hole when it is outside the event horizon, it will escape the black hole (but it will get redshifted by a lot), this is what I meant to say. Not sure if it answers your question though $\endgroup$
    – Harsha
    Oct 27, 2016 at 12:02
  • $\begingroup$ @Harsha why would light escape the black hole if emitted outside it? Won't it still be in its field and sucked into it? $\endgroup$ Oct 27, 2016 at 13:40

1 Answer 1


There is really two questions here.

One is if Hawking radiation gets absorbed (sucked in) by the BH. Generally it does not. The calculations were done to determine the output of that process (seen as two virtual particles, one sucked in and one escapes, or tunneling out; they are equivalent) at infinity. The ones that get created outside or tunnels out with enough energy (and right angular range), escapes, the other does not. The calculation determined how many escaped to infinity. So the radiation counted as emitted escapes. What does not is not counted

The second question is about the information. Neither thermal radiation nor Hawking, and both follow Plancks law, contain information. Thermal blackbody radiation is statistical and random at all times. They just mean that real emitted radiation from normal bodies (but mot radioactivity, say as an object burns) has information and we just abstract it by taking statistical averages. But then it is not exactly blackbody. Yes, blackbody is an idealization. But yes radioactive decay is truly random, and so is Hawking, and people do try to approximate true blackbody.

So, yes Hawking radiation is truly random and has no information other than the temperature; and the information paradox still needs a fully accepted resolution - the best bet is on the AdS/CFT correspondence that it somehow is on the horizon.

  • $\begingroup$ thanks! Could you please provide a link to a paper where the above calculations are done. Now after your answer I'm clear about the second part of my question, but my doubt still remains, why can't the radiation(the ones counted as limited escapes) get sucked back into the BH? $\endgroup$ Oct 26, 2016 at 17:26
  • $\begingroup$ Will do. A few hours, am on mobile phone now $\endgroup$
    – Bob Bee
    Oct 26, 2016 at 21:27
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    $\begingroup$ The original paper in pdf at itp.uni-hannover.de/~giulini/papers/BlackHoleSeminar/…. Lots more around. Wald's analysis paper, but not free at link.springer.com/article/10.1007/BF01609863. Wiki article with lots of references. Hawking is somewhat abstract some times, lots of people had to do their own calculations before they believed him. Google Hawking radiation or particle creation by black holes.en.m.wikipedia.org/wiki/Hawking_radiation $\endgroup$
    – Bob Bee
    Oct 26, 2016 at 23:51

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