IS BLACK HOLE A PERFECT BLACK BODY ??

Posted on Friday, October 26, 2012 by Arnab Roy

In this article I've tried to answer this Question because I've faced this myself from Several of my dear readers quite a lot of time..

To find the correct answer whether a Black Hole is a Perfect Black body of Thermodynamics or not..what we need to do is simple. We will Just Put our Giant astronomical friend to test and see whether or not it fits into all the required criterion for an object to be considered as a 'Perfect Black body' or not..

So here Goes the definition of a Black body..


A Black body is a physical substance, which can absorb all Electromagnetic radiation incident on it, regardless of the frequency or the angle of incidence..it does not reflect or transmit any fraction of the incident radiation whatsoever.


Also there is one more property of a perfect black body which will come to use later..


A Black body when in Thermal equilibrium to the surroundings emits the radiation which it absorbed earlier following Planck's law, which means that the spectrum which that emitted radiation will create if plotted in a graph paper will show that it's only dependent on the temperature alone and is not at all dependent on the body's shape or size.


Other than what I've mentioned, there are scores of other parameters as well by which we can compare between a black hole and black body but the definition and that one property which I've mentioned is more than sufficient to find what we are after..

Anyways..

So now let our monster enter the room..however..treat him a bit cautious !!! As it's Gravity is enough to convert you into a cosmic soup..

So..let's ask why a black hole is black at all ??..

That's because it absorbs all the Electromagnetic radiation that is incident on it, reflecting nothing just like a perfect black body in thermodynamics will do and Since it does not reflect any radiation..it 's not possible to detect it. But does it emit radiation following Planck's law.
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No..It does not emit radiation in a Thermodynamic sense..however there is obviously the existence of Hawking's radiation, but that's not what we would consider..and that has absolutely no relation with Planck's law of black body radiation..but from this we cannot conclude that a Black hole is not a perfect black body. In fact if you investigate a Schwarzschild black hole and a Kerr–Newman black hole, you will find that there are Quite a few similarities between a Black hole and a Perfect black body..but there are also some good number of thermal Properties that are exclusive to the black hole and a black body does not have any of them like a big boy kind of a stationary black hole will..


That means..a Black hole can be regarded one way or the other as a Perfect black body system but only if it's not of a global stationary nature..and is inherently dynamic. But to all fairness even then there would be discrepancies between the nature of the two..but still they will be quite close.


So when I wrote this article..I was rather confused !! While Purists suggest that Black holes should be considered as Perfect black bodies..I did think otherwise and in fact still do..I thought it's a rather Quantum phenomenon where the Photons are just getting trapped past the event Horizon and hence are to all fairness erasing their existence itslef from our Universe..Isn't it ??

 So how can we count for that Photon and..in itself ask Questions like these ???..

 Anyways thanx a lot for reading this..I'll look forward to Your views on this issue which I Guess you'll be sharing in the comment box below in a few moments from now..Adios !!!
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