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WaxRubiks
2015-Jul-10, 12:01 AM
The answer someone gave as to how Hawking radiation worked, was that pairs created near the event horizon had very specific location, so that would lead to very high uncertainty about their speed. Would this be true of ordinary matter as it approached the event horizon?
That is, as matter approached the event horizon, it would have less and less uncertainty about location, and atoms would acquire very high speed, and maybe become very hot?

Cougar
2015-Jul-13, 12:36 PM
The answer someone gave as to how Hawking radiation worked, was that pairs created near the event horizon had very specific location, so that would lead to very high uncertainty about their speed.

That doesn't seem to explain Hawking radiation, at least to me. The inversely related Heisenberg conjugate pair at issue is just that one that allows virtual particles to appear and disappear, i.e., the amount of energy vs. the length of time. Once they appear, the extreme gravity near the event horizon can pull one of the pair more strongly than the other, separating them so they cannot recombine and annihilate. They become real particles, promoted by the black hole's gravitational energy.

ShinAce
2015-Jul-13, 02:20 PM
The position of an electron in an atom is very much more constrained than a particle falling into a black hole. You we're given a hand waiving uncertainty argument, which is misleading.

Cougar has given a short, yet clear explanation of Hawking radiation.

Consider this, if it had to do with uncertainty, then why would Unruh radiation be so similar to Hawking radiation?

GarethMeredith
2015-Aug-14, 01:49 AM
You know, you don't even need Hawking radiation to see a glow round a black hole. There can be cases where black holes feed on charged particle clouds. The charged particles falling into a black hole will give off Larmor radiation, and a significant glow will occur.

malaidas
2015-Aug-14, 08:37 AM
Ok there's 2 new types of radiation I hadn't heard of. Time to go googling.

malaidas
2015-Aug-14, 08:51 AM
Ok if I am reading this right, the relationship between unruh radiation and hawking radiation depends on the apparent formation of an event horizon by the unruh effect. If so then such would for me suggest a reason for their similarity yes?

GarethMeredith
2015-Aug-25, 09:31 PM
yeah well, it should have been realized long before Unruh-Hawking radiation that any electron cloud around any strong gravitational hypersphere that those constituents of the field will naturally accelerate and give off radiation equal to the Larmor formula per charge. Hawkings way was not the ONLY way to observe a black hole or quasar.

ShinAce
2015-Aug-25, 11:21 PM
If you want to know a bit more about Unruh radiation, you can listen to Bill Unruh talk about it here:
https://www.youtube.com/watch?v=PqwIhjeRvXs

Gareth, the original question is not about being able to detect a black hole's presence. It's about the physics near an event horizon. Your trivial example of Larmor precession isn't appropriate as it assumes an external magnetic field. A black hole can be uncharged, and hence, have no magnetic field.

malaidas
2015-Aug-26, 12:05 AM
;
If you want to know a bit more about Unruh radiation, you can listen to Bill Unruh talk about it here:
https://www.youtube.com/watch?v=PqwIhjeRvXs

Gareth, the original question is not about being able to detect a black hole's presence. It's about the physics near an event horizon. Your trivial example of Larmor precession isn't appropriate as it assumes an external magnetic field. A black hole can be uncharged, and hence, have no magnetic field.

Cheers, great watching

GarethMeredith
2015-Aug-26, 12:06 AM
If you want to know a bit more about Unruh radiation, you can listen to Bill Unruh talk about it here:
https://www.youtube.com/watch?v=PqwIhjeRvXs

Gareth, the original question is not about being able to detect a black hole's presence. It's about the physics near an event horizon.

That is actually the boundary I speak of.

There is no crossroads

GarethMeredith
2015-Aug-26, 12:07 AM
Any electrically-charged cloud around a black hole will exhibit Larmor radiation.

ShinAce
2015-Aug-26, 12:51 AM
Do you have a source?

All I could find was this article, which refers to an uncharged black hole in a homogeneous external magnetic field:
http://link.springer.com/article/10.1007/BF00892482
click on 'look inside' to get the first two pages. The citation is before the first equation.

Reality Check
2015-Aug-26, 05:01 AM
Larmor radiation (https://en.wikipedia.org/wiki/Larmor_formula#Relativistic_generalization) is that any electrically charged particle that accelerates will radiate. An electrically charged particle in orbit around any body is accelerating. Thus there will be Larmor radiation from a charged particle orbiting any body including black holes.
Whether the radiation is physically significant (e.g. measurable) is another question! Too little acceleration and we cannot detect it. Too much acceleration and the charged particles spiral into the body - maybe too fast for us to detect.
ETA: There does not seem to be much literature on Larmor radiation in black hole environments. SAO/NASA Astrophysics Data System (ADS) (http://www.adsabs.harvard.edu/) has only 27 abstracts for 'larmor black hole'.