Hello, could someone pretty please explain what the interstellar medium is and what HI, HII, and molecular clouds are? Studying for a test and my book keeps mentioning them without unpacking the difference between these. Thank you.
In: Physics
The interstellar medium is the gas, dust, and radiation that exists between stars. Space is never perfectly empty. There are always some atoms or molecules of stuff in any given volume of space. It’s mostly hydrogen and helium with some heavier elements like carbon and oxygen. Molecular clouds are regions of the interstellar medium where hydrogen exists as a molecule. These regions can serve as “nurseries” for stars if there’s enough hydrogen to coalesce. An HI region is a cloud consisting mostly of neutral hydrogen and some other trace elements, and an HII region is a cloud of mostly ionized hydrogen. HII regions are often start-forming.
So to sum it up:
* Molecular cloud – Cloud of mostly hydrogen in its molecular form (H2) with some other elements.
* HI region – Cloud of mostly neutral hydrogen atoms with some other elements.
* HII region – Cloud of mostly ionized hydrogen atoms with some other elements.
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