The bright stars at the center of an H II region (an emission nebula) are mostly:

Question

Quizplus · Accepted Answer

H II regions are formed by ionized hydrogen gas, which is caused by the radiation of hot young stars. O and B stars are the most massive and hottest stars, which emit a lot of ultraviolet radiation capable of ionizing hydrogen gas. Therefore, the bright stars at the center of an H II region are mostly young O and B stars. Red supergiants and hot white dwarfs are not typically found in H II regions, and T Tauri stars are not massive enough to ionize hydrogen gas.

The Bright Stars at the Center of an H II