AST 112 Study Guide - Midterm Guide: Dark Matter Halo, Spiral Galaxy, Satellite Galaxy
Document Summary
Stars divided into 3 different populations according to age: population i: stars born in spiral arms of galaxies. Some born very recently, associated with star formation regions. Atmospheres contain lots of metals: population ii: stars in haloes and bulges of spiral galaxies, following elliptical orbits. Older stars, whose atmospheres contain few metals: population iii: first generation of stars, ancient, with no metals (just hydrogen and helium). Using ultraviolet light we discover that massive young stars are concentrated in the arms of spiral galaxies. Measuring hydrogen emissions also helps us find massive stars forming in the spirals. In red/infrared light, older stars are seen to be less concentrated in arms. Recent star formation only happens in the arms of spirals dust lanes . There is a lot more mass in the galaxy than we can account for . Using kepler"s law we can predict velocities of stars orbiting the galaxy, but actual velocities are different.
