What mechanisms or physical processes are responsible for the emission of electromagnetic radiation in a galaxy in the different wavelength bands?


closed as too broad by Kyle Kanos, Emilio Pisanty, sammy gerbil, Chris, Mitchell Jan 31 '18 at 6:08

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    $\begingroup$ This is pretty broad as there are a wide variety of sources and processes across the whole EM spectrum. You may want to consider narrowing it down to one waveband you are interested in, otherwise this is likely to be closed as too broad. $\endgroup$ – Kyle Kanos Jan 30 '18 at 15:35
  • $\begingroup$ I'm not looking for an detailed answer, I just want to have an ideia of what is happening in galaxy when it emits infrared or milimetric for example $\endgroup$ – user3636673 Jan 30 '18 at 15:37
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    $\begingroup$ This question is somewhat akin to asking, "I just want to have an idea of what is happening when I walk around the city and I hear sounds." $\endgroup$ – Solomon Slow Jan 30 '18 at 15:55

Most of the non-darkmatter mass of the galaxy is in the form of plasma or neutron density neutron stars and black holes. Almost all of the gamma ray photons originate from the nuclei of the various elements in the plasma as they fuse together to form new elements, matter-antimatter annihilation, gamma ray burst events, or emissions from nucleons relaxing back to ground quantum states of nuclear isomers.

X-rays can also originate from relaxing nucleons, but for lower quantum energy drops than gamma rays. A good portion of the x-ray spectrum comes from plasma and electrons being accelerated into black holes or neutron stars but colliding with charged plasma on the way. In fact, these x-ray emissions from Cygnus x-1 led to the first evidence of black holes.

Although photons of almost every frequency are emitted by supernovae explosions, a huge proportion of the spectrum emitted is in the x-ray range. This due again to the very great acceleration or deceleration (Bremsstrahlung) of plasma nuclei and electrons through magnetic and electrical fields in plasma resulting from the supernova explosions. The study of distant supernovae was one of the main reasons for launching the Chandra x-ray space telescope.

The rest of the lower frequencies of photons which include UV, visible, IR, and radio mainly include the following sources:

  • $\begingroup$ Yes even in the darkest vacuum space is filled with radiation. $\endgroup$ – Bill Alsept Jan 30 '18 at 16:05
  • $\begingroup$ Nice short answer! I only wonder where the gamma rays with energies higher than the annihilation of nucleon anti-nucleons are produced. $\endgroup$ – freecharly Jan 30 '18 at 18:19
  • $\begingroup$ I'd add: VIS, IR, millimeter from atoms and molecules around cold sources, millimeter and radio from synchrotron radiation from electrons + ions $\endgroup$ – AtmosphericPrisonEscape Jan 30 '18 at 18:24
  • $\begingroup$ @freecharly They could be produced from binary star systems containing compact objects. That is according to one example. $\endgroup$ – Bill Alsept Jan 30 '18 at 21:42
  • $\begingroup$ @Bill Alsept - Thank you! I will do a search on that. It is also interesting what the highest measured energies of gamma photons actually are and where they were produced. $\endgroup$ – freecharly Jan 30 '18 at 22:26

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