Does Hawking Radiation preclude EH formation?

In summary: Also, as PAllen pointed out, for the emission of radiation to cause the BH to "evaporate", the radiation has to escape to infinity. (That's another assumption underlying the Hawking calculation, btw; the calculation doesn't work if the radiation doesn't escape to infinity.) Clearly that can't happen at the center of a neutron star. Even if such radiation were to form at the center of a neutron star when the horizon first forms, all it will do is increase the pressure at the center, but if the star starts out larger than the Schwarzschild radius, the radiation will quickly escape.
  • #36
PeterDonis said:
AFAIK nobody has seriously considered that question; but I'm not intimately familiar with the entire literature on this topic. Off the top of my head, I would say that Hawking radiation requires a locally trapped surface, i.e., an apparent horizon, and a trapped surface doesn't form until the collapsing object is entirely within r = 2M. But I haven't seen any math addressing this.

That was my intuition as well, but I didn't want to state it without some backing (either from literature or understanding well enough how to apply the derivation(s) of Hawking radiation to the given scenarios). If this intuition is right, it still says Hawking radiation begins not only when all matter is at finite density, but even when there might no matter at all near 'where the singlularity will be'.
 
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  • #37
The Visser review references Nielsen's paper which discusses "Perhaps strongest reason for focusing on event horizons instead of apparent horizons was the belief that if an apparent horizon exists then it must lie behind the event horizon and so cannot influence the outside region anyway. As we will now see, this belief was predicated on a condition that is most probably violated by Hawking radiation. ...If one allows the possibility that a black hole spacetime will eventually stop accreting matter and start evaporating by the Hawking process, once must face the possibility that locally defined horizons, based on marginal surfaces, maybe located outside the event horizon, at least for some period of the lifetime of the black hole. In fact, the violation of the null energy condition opens up the further possibility that there is no event horizon at all and all one need consider is the trapping horizon"
 
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