AST 309 Chapter Notes - Chapter 7: Spiral Galaxy, H Ii Region, Star Formation
Document Summary
Hii regions are emission nebulae created when young, massive stars ionize nearby gas clouds with high-energy uv radiation. Composed primarily of hydrogen, and have temperatures of around. Can extend over several hundred light years, or be so compact they don"t stretch 1 light year across. Have a large range of densities, from a few atoms/cm^3 to millions of atoms/cm^3. In our galaxy, they follow a distribution pattern similar to that of molecular clouds, and are similarly concentrated in the spiral arms of other galaxies. Also found in association with newly formed stars throughout irregular galaxies making them highly visible traces of active star formation. Their lifespans are only a few million years, and they place a key role in the propagation of star formation during this time. Winds and uv radiation emitted by massive stars irradiate the gas in the. Hii region, and carve out a cavity in the surrounding molecular cloud.
