What is an H II region?
Q: What is an H II region?
A: An H II region is a region where huge blue stars are formed from hydrogen, and they are named after the ionised atomic hydrogen which they produce.
Q: How do these regions form?
A: The stars form inside a large cloud of hydrogen gas, and the short-lived blue stars formed in these regions give off huge amounts of ultraviolet light which ionizes the surrounding gas.
Q: How big can H II regions be?
A: They can be several hundred light-years across.
Q: When was the first known H II region discovered?
A: The first known H II region was the Orion nebula, which was discovered in 1610.
Q: What happens to an H II region over time?
A: Over several million years, thousands of stars will be born in the region, eventually producing a star cluster. Supernova explosions and strong stellar winds from the most massive stars will then blow away the gases of the H II region, leaving behind a cluster of stars such as the Pleiades.
Q: Where can we find extragalactic H II regions?
A: Extragalactic H II regions can be seen at huge distances in the universe and their study helps to fix the distance and chemical composition of other galaxies. Spiral and irregular galaxies have many H II regions while elliptical galaxies have almost none - spiral galaxies like our Milky Way usually have them concentrated in their spiral arms but irregular galaxies tend to have them distributed randomly throughout their space.
Q: Are there any particularly large examples of an H II Region?
A Yes - some galaxies have huge H II Regions with tens of thousands of stars such as 30 Doradus in Large Magellanic Cloud or NGC 604 in Triangulum galaxy
