what are it's features?
It vary greatly in their physical properties, their size is also known as the Stromgren radius and essentially depends on the intensity of the source of ionising photons and the density of the region, their densities range from over a million particles per cm³ in the ultra-compact H II regions to only a few particles per cm³ in the largest and most extended regions
H II region
H II regions vary greatly in their physical properties. They range in size from so-called "ultra-compact" (UCHII) regions perhaps only a light-year or less across, to giant H II regions several hundred light-years across. Their size is also known as the Stromgren radius and essentially depends on the intensity of the source of ionising photons and the density of the region. Their densities range from over a million particles per cm³ in the ultra-compact H II regions to only a few particles per cm³ in the largest and most extended regions. This implies total masses between perhaps 100 and 10 solar masses.
where could be found hii emission nebula regions Sometimes several hundred light-years across, are often associated with giant molecular clouds what does this region mean? It is a region of interstellar atomic hydrogen that is ionized how did it get the name? The term H II is pronounced "H two" by astronomers. "H" is the chemical symbol for hydrogen, and "II" is the Roman numeral for 2.
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H II region [SEP] Physical properties
There are also "ultra-dense H II" regions (UDHII). Depending on the size of an H II region there may be several thousand stars within it. This makes H II regions more complicated than planetary nebulae, which have only one central ionising source. Typically H II regions reach temperatures of 10,000 K. They are mostly ionised gases with weak magnetic fields with strengths of several nanoteslas. Nevertheless, H II regions are almost always associated with a cold molecular gas, which originated from the same parent GMC. Magnetic fields are produced by these weak moving electric charges in the ionised gas, suggesting that H II regions might contain electric fields.