ASTR 1103 Lecture Notes - Lecture 14: Thin Disk
9 Feb 2020
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Document Summary
Age of the galaxy: disk - 9 billion years, halo - 13 billion years. Stellar populations: population i, disk population, metal-rich 2-3, young stars, population ii, halo population, metal poor < 0. 1, very old stars. Abundance of elements: hydrogen and helium, the two lightest elements, are by far the most abundant elements in the universe. History of the galaxy: monolithic collapse model an early hypothesis that says that the galaxy formed from the collapse of a single large cloud of turbulent gas over. Observations confirmed by model: star populations with different compositions, thin disk (300ly) contains metal rich stars with circular orbits in the galaxy, age of clusters. Shortfalls and changes of model: not all globular clusters have the same age, some of the younger clusters are in the outer halo. Bottom up model: new hypothesis, high-mass stars formed in original cloud and died quickly, small galaxies captured. It is a region of complex magnetic fields and rapid star formation.
