NGC 604, a giant H II region in the Triangulum Galaxy

An H II region is a region o interstellar hydrogen that is ionised.[1] It is teepically a lairge, law-density clood o pairtially ionised gas in which starn formation haes recently taken place.


  1. Ian Ridpath (2012). A Dictionary of Astronomy (2 rev. ed.): H II region. Oxford University Press. ISBN 9780199609055. Retrieved 24 December 2015.