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HI region




An interstellar cloud composed primarily of atomic hydrogen, detectable by its radio wave emission in the 21-centimeter line. HI regions have a density of 1 to 10 atoms/cm3 and a temperature of about 125 K (the spin temperature of neutral hydrogen). At least 95% of interstellar hydrogen is HI.


Related category

   • INTERSTELLAR AND INTERPLANETARY MATTER