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It is very well know that above zero Kelvin every body emits thermal radiation

  1. What about other form of radiation such as gamma, x- ray, radio waves etc.?

  2. And will our most precise instruments will not be able to detect the presence of any body/matter at absolute zero in absence of any external light source?

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closed as unclear what you're asking by CuriousOne, ACuriousMind, John Rennie, sammy gerbil, peterh Aug 1 '16 at 0:38

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  • $\begingroup$ Thermal radiation is being emitted by a body in thermal equilibrium. If anything else comes out, then the body is not in equilibrium and talking about a temperature doesn't make sense. T=0 is simply ruled out by the third law of thermodynamics. $\endgroup$ – CuriousOne Jul 31 '16 at 4:42
  • $\begingroup$ The first two statements of yours seems absurd and about the last I agree with it but what if it Is an ideal process i.e. no entropy change takes place $\endgroup$ – Rohit Joshi Jul 31 '16 at 4:48
  • $\begingroup$ What sounds absurd to you? That there are bodies that don't have a temperature? You want an ideal process? How much time and money do you have? I am being paid by the hour and ideal processes take infinitely long, i.e. they are unphysical and expensive to observe. $\endgroup$ – CuriousOne Jul 31 '16 at 4:52
  • $\begingroup$ Then why the hell we study ideal process if they physically not possible considered the exmaples of Carnot Engine ( internally reversible) Blackbodies( ideal) we do not construct these bodies but we are rather curious to know how they work, so whats the problem in having a body at absolute zero, $\endgroup$ – Rohit Joshi Jul 31 '16 at 4:58
  • $\begingroup$ So you know what you can never achieve in reality, but mostly because the complete mathematical description of non-ideal processes is much, much harder. There is nothing wrong with having a body at absolute zero, except that nobody has ever seen one. Science is generally supposed to describe what has been observed and those things have not. $\endgroup$ – CuriousOne Jul 31 '16 at 5:10
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"gamma, x- ray, radio waves" are the same as thermal radiation - the difference only depends on the temperature of the source.

Objects at very low temperatures emit mostly longer wavelength radiation, as they heat up the radiation goes to shorter wavelengths. Very hot objects emit x-rays

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  • $\begingroup$ Although generally, gammas are considered as the photons emitted from nuclear transitions, not electronic. I suppose at high enough temperatures and densities they would be part of the black body spectrum. $\endgroup$ – Jon Custer Jul 31 '16 at 13:52
  • $\begingroup$ Yes - I couldn't think of an astronomical thermal gamma ray source. But there are thermal x-rays from accretion disks. $\endgroup$ – Martin Beckett Jul 31 '16 at 22:10
  • $\begingroup$ It's an interesting question- what conditions would lead to gammas being part of a 'thermal' spectrum. Neutron star formation phase? $\endgroup$ – Jon Custer Jul 31 '16 at 23:09

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