# How are stellar EM radiation formed?

1. Jun 15, 2012

### ehabmozart

How are stellar EM radiation formed??

I've read this in many books and sites... Any object above 0 K will emit EM radiation of all wavelengths... Now this is confusing me a lot... I mean, how for example a sun emit wavelength s of a Radio and it is the same sun which emits ultra violet and gamme rays.. How is it possible to emit all kind of wavelengths. Being particular, when we look at a star by prism method, how can we detect an O star which has it's peak wavelength beyond visible light i guess... Finally, why is a peak wavelength formed. Thanks in advance to whoever gives me a good reply!

2. Jun 15, 2012

### krd

Re: How are stellar EM radiation formed??

This was confusing me too. But I think I found the answer.

Atoms will emit photons at discrete wavelengths - so you can see characteristic lines for gases like hydrogen etc.

Then there is black body radiation - which is a continuous spectra.

And how this happens. When a body is hot, the atoms jiggle against each other, which causes their electro-magnetic fields to interact. This effectively creates lots of phonons - since atoms movements are largely random you get a broad band of wavelengths - a continuous spectra. Some atoms are moving very fast and some are moving very slowly - two fast atoms hit each other head on they'll slow down to a crawl, and then you'll get a radio wave phonon..........and the effect is you can get light with really long wavelengths.

The phonons become photons when they leave the body and travel into empty space.

When a body gets hotter - the intensity of the continuous spectra increases - and because the atoms are moving faster, the peak frequency of the spectra gets higher. And you can tell the temperature of a body by knowing the peak frequency of the black body radiation it's emitting.

There's some lovely formulas too, than govern what you see in the spectra.........which I can't remember.........If anyone else does?

3. Jun 15, 2012

### Bob S

Re: How are stellar EM radiation formed??

Also, spiraling relativistic electrons in magnetic fields near astronomical objects (e.g., Crab nebula) emit a continuous wavelength EM spectrum called synchrotron radiation. See http://en.wikipedia.org/wiki/Crab_Nebula