Answer to Question #87197 in Astronomy | Astrophysics for Amit

Question

What is the difference between the HII region and HI region of the interstellar medium? Explain the process involved in the detection of HI region in the ISM.

Answer 1

HII and HI regions are the regions of hydrogen.

The HI clouds are the regions of neutral Hydrogen atoms, whereas HII - regions of of ionized H+ ions (protons).

HI regions are usually detected through 21 cm emission line, which is observed with radio-telescopes.