Detecting hydrogen inside IMC's and GMC's

[dougettinger]

I am looking for a brief summary of current hydrogen detection within galaxies.

How are H I and H II detected? Is there a minimum required temperature and/or density ?
How is molecular hydrogen detected? Is this the only form of hydrogen with sufficient density that can become opaque thereby creating Bok globules?

Gas to gas, Doug Ettinger

 

[mathman]

I can't address the details. However, in general, hydrogen at high temperature has its own characteristic lines in spectra. At low temperature, hydrogen is detected by light shining through it (gas clouds) where the hydrogen lines show up as darkening.

 

[Drakkith]

This article had some information that might answer some of your questions.
http://en.wikipedia.org/wiki/Molecular_cloud

 

[dougettinger]

I remember reading that hydrogen cannot be detected by emission lines below 100 degrees Kelvin. So below this temperature how is hydrogen detected ?

Hydrogen is in basically three forms in interstellar space: only one proton, one proton and one neutron, and a hydrogen molecule, H2. Are all these forms equally detectable ? Does each type of isotope prefer a certain temperature range?

Regards, Doug Ettinger

 

[pmacias]

Currently, hydrogen (H) detection within galaxies is primarily done through the use of radio telescopes. This is because hydrogen emits a specific wavelength of light at 21 centimeters (cm), which can be detected by radio telescopes. This method allows scientists to map the distribution and movement of hydrogen gas within galaxies.

H I (neutral atomic hydrogen) and H II (ionized atomic hydrogen) can be detected through their 21 cm emission using radio telescopes. However, the detection of H II requires a higher density of hydrogen gas compared to H I. The minimum required density for H II detection is typically around 100 atoms per cubic centimeter (cm^3).

Molecular hydrogen (H2) can also be detected through its rotational and vibrational transitions at infrared and radio wavelengths. However, the detection of H2 is more challenging as it requires higher temperatures and densities compared to atomic hydrogen. The minimum required density for H2 detection is typically around 10^3-10^4 atoms per cm^3.

Bok globules, which are dense, dark clouds of gas and dust in space, are primarily composed of molecular hydrogen. However, other forms of hydrogen, such as H I and H II, can also contribute to their opacity. The high density of molecular hydrogen in Bok globules is what allows them to become opaque and create the dark patches we see in the night sky.