are x-ray,uv, microwaves considered thermal radiation?

Question

I am trying to connect everything. so in the electromagnetic spectrum, i know that infrared and visible lights are thermal radiation. It also says that anything above absolute zero temperature emit thermal radiation. So does that mean other radiations in the electromagnetic spectrum are duet to thermal radiations??

Answer 1

If an object is hot enough, it can emit significant amounts of electromagnetic radiation anywhere in the spectrum, including ultraviolet light and x-rays. Things really have to get hot to emit significantly at these energies, but if they get hot enough, they emit a lot of it.

Blackbody thermal radiation in the microwave region is very weak even from very hot bodies, but it exists. It doesn't take much heat to emit in the wavelengths corresponding to microwaves. Objects at room temperature emit almost as much thermal microwave radiation as much hotter objects, little though that may be.

This is far from making the blanket statement that radiation in the electromatic spectrum actually is due to thermal radiation; only that it can be. Lasers and the line spectra from electrically excited gases, the output of manmade electromagnetic oscillators are examples of electromagnetic radiation produced nonthermally. At least, it isn't thermal radiation in the conventional blackbody sense.

Incidentally, it is by looking at the background (thermal) radiation in the microwave part of the spectrum that astronomers have determined the direction and speed of the earth with respect to the universe as a whole.

Answer 2

Yes - electromagnetic radiaiton can be caused by heat. Even x-rays if teh heat source is hot enough. Consider that a photon with an energy of 1/40 eV is equivalent to the thermal energy at room temperature. X-rays are in the keV (thousand eV) region so you'd need a heat source at a temperature of 40,000 time room temperature or about 800,000 C. Nuclear explosions and centers of stars approach these kinds o temperature.

Answer 3

All electromagnetic radiation can be thermal. It just takes a source with the appropriate temperature.

1K will produce microwaves.
1000K will mostly produce IR radiation.
5000K will be right smack in the visible (sun!).
10000K will be in the near UV and higher temperatures will be in the far UV and x-ray region.
Near black holes matter can be heated to temperatures where mostly x-rays and low energy gamma rays are being produced.

I am not aware that there are processes in or near thermal equilibrium which will produce high energy gammas (>>1GeV). But I might be wrong. It is not impossible, after all, but it would take incredible power sources to heat even small amounts of matter that high.