Does Hawking Radiation preclude EH formation?

PeterDonis

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.

PAllen

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'.

atyy

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"