Re: What is the difference in production at the atomic level of EM energies?

It's a good bit more complex than what you've mentioned, actually. Bremsstrahlung, for example, creates some of the highest-energy gamma rays. One difficulty here is that we have arbitrary human ranges which we've applied to the electromagnetic spectrum. Another is that there are many, many mechanisms of generating electromagnetic radiation. For example, hot objects emit a range of radiation: http://hyperphysics.phy-astr.gsu.edu/Hbase/wien.html

Hot objects emit radio waves, microwaves, infrared, and can (if hot enough, such as some types of violent astrophysical objects) emit significant amounts of their radiated energy in a continuous spectrum all the way up to the x-ray range.

Emission at discreet wavelengths requires an antenna or emitter of comparable wavelength or energy. Microwaves and radio waves are often emitted by molecular transitions. Infrared and visible light are often emitted by transitions of electrons in atomic energy levels. UV usually involves high-energy hydrogen energy level transitions or the capture of electrons by ions, causing photons in the UV range to have damaging energy (they can break chemical bonds or ionize atoms, causing chemical damage).

High-energy electrons orbiting in magnetic fields of objects like neutron stars can emit a spectrum of synchrotron radiation, as well. This radiation due to the acceleration of a charged particle is more complex and similar to Bremsstrahlung radiation: http://hyperphysics.phy-astr.gsu.edu/hbase/particles/synchrotron.html

There are indeed many such mechanisms. Some photons (Google [cosmic microwave background radiation ] for details or see here: http://map.gsfc.nasa.gov/m_uni/uni_101bbtest3.html ) are left over from the creation of the universe! Astronomers wouldn't have so much work to do if the answer weren't so complex.

If you want a bottom-line answer, though, I believe that most of the light we see from stars in space is thermal (see above with Wien's displacement law and blackbody radiaton). Peaks and especially absorption lines exist within this continuous spectrum, but the total amount of power we see coming from space is dominated by thermal emission.