région H II

CONT: La partie restante relativement petite du milieu diffus entoure les étoiles chaudes qui l'ionisent par leur rayonnement. On y rapporte les nébuleuses diffuses, les champs d'hydrogène, les radiosources métriques. A la différence des premières, ces zones s'appellent régions H II.

CONT: Since hydrogen is the main constituent of the gas, we often characterize a region of interstellar space according to whether its hydrogen is neutral-an ""H I region"" - or ionized-an ""H II region"". The gas in the H II regions glows by the process of fluorescence. The light emitted from these regions of ionized gas consists largely of emission lines, so they are also called ""emission nebulae"".