Physics Help Forum BlackHole-gravity or temperature
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 Jun 27th 2017, 06:16 AM #1 Member   Join Date: May 2017 Location: tampa bay florida Posts: 31 BlackHole-gravity or temperature Supposedly the gravitational pull of Black holes is so intense that not ever light can escape. Isn't this nonsense? The temperature of a BH is near absolute zero. At Zero there is no light being created or attempting to escape. So the blackness of a BH is due to temperature not gravity, correct?
 Jun 27th 2017, 12:33 PM #2 Senior Member   Join Date: Nov 2013 Location: New Zealand Posts: 534 I am told that black holes do in fact radiate energy, something called Hawking radiation, so not sure its temperature is zero.
 Jun 27th 2017, 12:39 PM #3 Member   Join Date: May 2017 Location: tampa bay florida Posts: 31 Quite form Physics.org "The most massive black holes in the Universe, the supermassive black holes with millions of times the math of the Sun will have a temperature of 1.4 x 10-14 Kelvin. That's low. Almost absolute zero, but not quite."
Jun 27th 2017, 02:03 PM   #4

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 Originally Posted by kiwiheretic I am told that black holes do in fact radiate energy, something called Hawking radiation, so not sure its temperature is zero.
 Originally Posted by wad Quite form Physics.org "The most massive black holes in the Universe, the supermassive black holes with millions of times the math of the Sun will have a temperature of 1.4 x 10-14 Kelvin. That's low. Almost absolute zero, but not quite."
Hawking radiation is a quantum phenomenon. The idea is that you can have a particle-antiparticle pair occur very close to the horizon of the hole. The antiparticle then falls into the hole, decreasing the hole's mass by a little and the other particle then flies away which is the radiation that is measured. (Don't ask me why it is the antiparticle going down the hole. There's some sort of thermodynamic process going on there.)

So, yes, the black hole will radiate energy in terms of an outflux of particles which gives it a "temperature."

-Dan
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 Jun 27th 2017, 04:14 PM #5 Member   Join Date: May 2017 Location: tampa bay florida Posts: 31 True - there may some particles that escape as "radiation" very slowly and over hundreds of billions of years, but the notion that "light" (as photons or waves) cannot escape a black hole because of the enormous gravity is specious. There is no light to escape because of the temperature. That gravity is holding light back is a widely held yet incorrect concept.
 Jun 27th 2017, 04:15 PM #6 Member   Join Date: May 2017 Location: tampa bay florida Posts: 31 sorry" over hundreds of millions of years"
Jun 27th 2017, 04:40 PM   #7

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 Originally Posted by wad True - there may some particles that escape as "radiation" very slowly and over hundreds of billions of years, but the notion that "light" (as photons or waves) cannot escape a black hole because of the enormous gravity is specious. There is no light to escape because of the temperature. That gravity is holding light back is a widely held yet incorrect concept.
The particle-antipartical pair are on the limits of that. One goes in, one escapes. The escaped particle is what tells you the "temperature."

I'm not clear on what you are referring to. "the notion that "light" (as photons or waves) cannot escape a black hole because of the enormous gravity is specious." The horizon of the hole (defined to be at the Schwartzchild radius) is the limit where the escape speed from the hole is the speed of light. What exactly are you saying is wrong?

-Dan
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 Jun 28th 2017, 08:40 AM #8 Member   Join Date: May 2017 Location: tampa bay florida Posts: 31 I understand the Schwartzchild (gravitational radius) and the radius is directly proportional to the mass of the black hole by [2GM / c^2 ], but this is my point. It is true that light, if there were any to escape, could not because of the mass / gravity of the BH. My point simply is that in the first place there is no light to escape because the temperature of the BH is near zero. This is why the black sphere ("hole") is black.

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