AnH II region is a region where hugeblue stars are formed fromhydrogen. They are named after theionisedatomichydrogen which they produce: H II.[2]
Thestars form inside a large cloud of hydrogengas. The short-lived blue stars formed in these regions give off huge amounts ofultraviolet light. This ionizes the surrounding gas.
H II regions can be several hundredlight-years across. The first known H II region was theOrion nebula, which was discovered in 1610.[3] These regions have extremely varied shapes. They often appear clumpy and filamentary, sometimes showing bizarre shapes such as theHorsehead nebula.
H II regions give birth to thousands of stars over several million years. Eventually, this produces astar cluster. In the end,supernova explosions and strongstellar winds from the most massive stars blow away the gases of the H II region. This leaves behind behind a cluster of stars such as thePleiades.[4]
H II regions can be seen at huge distances in the universe.The study of extragalactic H II regions helps to fix the distance and chemical composition of othergalaxies.
Spiral andirregular galaxies have many H II regions, whileelliptical galaxies have almost none. In spiral galaxies, like theMilky Way, H II regions are found in thespiral arms, but in the irregular galaxies they are distributed atrandom.
Some galaxies have huge H II regions, with tens of thousands of stars. Examples include the30 Doradus region in theLarge Magellanic Cloud andNGC 604 in theTriangulum galaxy.
