Heating/Cooling in the ISM

1. Mar 31, 2013

vikasagartha

Hi! I am an student w/ little background in astronomy taking an upper level astro course, and am having some difficulty with basic concepts. Any help is appreciated.

Why are cosmic rays so important for the heating of molecular clouds? I read that hard xrays can heat as well, while soft xrays cannot. Help?

2. Mar 31, 2013

mathman

Cosmic rays are mostly protons, not photons.

Last edited: Mar 31, 2013
3. Mar 31, 2013

cepheid

Staff Emeritus
Welcome to PF,

I'm not 100% sure of the answer (not an ISM guy), but the relative importance of various heating mechanisms might have something to do with the optical depth of molecular clouds as well (which is large, in the visible). It could be that hard X-rays (and cosmic rays) can simply penetrate farther. Take this with a grain of salt. This is not a question that is too basic or to which you should already know the answer. Ask for clarification in your class!