[Kryptid]

Again, no. Whether or not a photon is blue shifted or red shifted depends on whether or not it is moving into or out of a gravity well. Stating that a photon is blue shifted because it is near a strong source of gravity is incorrect because you have not defined the direction of movement.

If you acknowledge the accuracy of the calculator, then you accept that stellar mass black holes produce primarily radio waves, not gamma rays.

[samcottle (OP)]

Well, is a photon deposited just beyond the event horizon of a black hole moving "into" or "out of" a strong gravitational field?

[Kryptid]

That depends upon its direction of travel. Some will be traveling towards the hole before passing the event horizon. Those would be blue shifted. Some will be moving away from the black hole and thus red shifted.

[samcottle (OP)]

No, we were talking about Hawking radiation. Yes, incoming radiation will be blueshifted, but any radiation deposited near the event horizon will also be blueshifted. If, in the unlikely event a photon deposited near the event horizon of a strongly-gravitating black hole were to escape the gravity of a black hole to a degree sufficient to allow it to redshift, then it would become redshifted. That does not mean that the photon is not a gamma photon at the point of being emitted by the black hole; it means only that any radiation we observe coming from sufficiently large black holes is microwave or radio wave radiation. The implication here is that this radiation has been allowed to travel a sufficient distance from the black hole to allow it to be redshifted. Because it is, in general, very unlikely that any radiation can escape a black hole's gravity, we only observe black holes in the radio/microwave part of the EM spectrum. As for smaller black holes (and larger black holes, when they eventually evaporate) radiate away (which they do so far more quickly than a larger BH) they give off a burst of gamma rays. This much is well-established. Giving a probabilistic underpinning to the phenomenon of Hawking radiation and the information escape paradox; through invoking an idea of gravitational electron densities (i.e. clouds of electrons forming gravitational fields); allows us to gain some quantum-gravitational perspective on this matter. In standard GR, Hawking radiation would never be possible; any light emitted at the horizon would just fall straight back in. In a quantum conception of gravity, there exists (I guess) a small probability of a photon emitted by the black escaping its gravity entirely. This is because it might be reflected by these background electrons in just the right way, or hit the right sequence of electrons that don't absorb it again (if, say, their energy levels are too high), and by a quirk of fate it manages to escape (which, as I've said, is very unlikely for very massive black holes). That said, I grant you that, if it does manage to escape, it will probably undergo redshift and eventually become a micro- or radio wave photon.

[Bored chemist]

I'm still waiting for a reasonable reply to this.

Where did I say anything that looked like I said anything about the effects of gamma rays?

primordial black holes have been observed to evaporate in a burst of gamma radiation. That *is* Hawking radiation

Can you show where anyone has observed the evaporation of a primordial BH?
Also, do you not realise that the radiation is emitted over the life of the BH, not at the end.

[Bored chemist]

Well, is a photon deposited just beyond the event horizon of a black hole moving "into" or "out of" a strong gravitational field?

If it falls in  then we don't get to see it.
If it is Hawking radiation then comes out .
And if it comes out it has to "climb" out against the gravitational pull of the BH and will be red shifted.

[Bored chemist]

Perhaps no one here is wrong, per se, and we're talking somewhat at cross purposes, but the truth stands; HR is always gamma rays initially unless said radiation gets far enough away from the black hole to allow it to become redshifted.

But it's only HR after it has left the BH.
When it's created it's annihilation radiation.

[samcottle (OP)]

https://academic.oup.com/mnras/article/283/2/626/988213?login=false
I think 'can' is the operative word here. I suspect primordial black holes are likely and that we've observed their evaporation in the gamma-ray bursts detailed in this paper. I also suspect the LHC detection of two gamma-ray photons as the decay products of the so-called Higgs boson were the decay products from a naked singularity (which would be consistent with our theories on black hole physics). Perhaps the term 'observed' was a little strong on my part. Also, perhaps you weren't suggesting that gamma rays couldn't act as thermal radiation, though at the time you seemed to be. The point I was driving at with Hawking radiation is that any radiation emitted by a black hole near its event horizon is Hawking radiation. This is true if it's a small black hole that quickly evaporates or a large one that takes eons to evaporate. In the case of small black holes, we'd see a burst of gamma rays (since it has less gravity to pull the radiation back in); in the case of larger black holes, we'd see only radio waves or microwaves since only a small proportion of that radiation is able to escape the huge forces of the black hole's gravity field and will become redshifted in the unlikely event it escapes to a sufficient distance to be observed. In either case, the radiation is still Hawking radiation, and it still all starts out as gamma rays.

[Bored chemist]

Also, perhaps you weren't suggesting that gamma rays couldn't act as thermal radiation, though at the time you seemed to be.

How did you come to that mistake?

[Bored chemist]

Perhaps the term 'observed' was a little strong on my part.

Because it simply isn't true, is it?
Show me the reports of observations of gammas from primordial BH, or admit that what you said was not true.

[Bored chemist]

we'd see a burst of gamma rays

The calculator shows how long that "burst" would be.
A 3.34 E 10 tonne  BH would emit gammas.
The lifetime is about a million times longer than the history of the universe.

[samcottle (OP)]

Anything smaller than that would also. Anything larger than that would also. What we detect from anything larger than that (or, 'much larger) would be INITIALLY gamma radiation undergoing a subsequent redshift. I don't think there's much more that needs to be said.

[Kryptid]

I see you told Bored Chemist to post a source for his claims. I would now like to ask you to do the same. Please post a source that supports your claim that Hawking radiation starts off as gamma rays.

[samcottle (OP)]

https://link.springer.com/article/10.1007/BF02676709?noAccess=true

[samcottle (OP)]

It would be anyway because of GR.

[Kryptid]

That link is about primordial black holes. I am talking about stellar mass and supermassive black holes.

[samcottle (OP)]

The size of the black hole is irrelevant. I think I've basically pointed this out already. So I don't start sounding like a broken record, perhaps I'll try and put it somewhat differently. From what theory tells us about smaller black holes, we infer that larger black holes, as they evaporate away, will end their lives in a burst of gamma radiation. Prior to that point, they are giving off gamma radiation, all the time; the overwhelming majority of it falls straight back into the black hole, some manages to escape the black hole's colossal gravitational forces, and find its way into space whereupon it's become redshifted. Any photons 'created' (again, a notion I reject; though my rejection of it is not so relevant in this argument) anywhere close to the event horizon of a black hole will be subject to huge gravitational forces and, hence, blueshifting. Again, some do manage to escape and become redshifted eventually. In any case, they start out as gamma photons. I suspect this comes down to the collosal forces present in black hole interiors due to their huge densities and pressures; any photon caught up in all that material (whatever it is; quark-gluon plasma, or whatever) will, of course, be, in essence, blueshifted.

[Bored chemist]

Any photons 'created' (again, a notion I reject; though my rejection of it is not so relevant in this argument) anywhere close to the event horizon of a black hole will be subject to huge gravitational forces and, hence, blueshifting.

If we see it then it has got out of the BH and will have been red shifted.

[samcottle (OP)]

As I said, yes.

[Bored chemist]

As I said, yes.

What you very clearly said was

Any photons 'created' (again, a notion I reject; though my rejection of it is not so relevant in this argument) anywhere close to the event horizon of a black hole will be subject to huge gravitational forces and, hence, blueshifting.

Do you realise that blue is not red?