ASTR 103 Lecture Notes - Lecture 14: Horizontal Branch, Stellar Kinematics, Mass Transfer
Document Summary
Understanding how stars evolve requires both observations and ideas from physics. Because stars shine by thermonuclear reactions, they have a finite life span. When the lighter elements are depleted, there is nothing left to fuse. ~ that is, they fuse lighter elements into heavier elements. Interstellar gas and dust are concentrated in the disk of the galaxy. Interstellar gas and dust is ubiquitous the galaxy. Clouds within the interstellar medium are called nebulae. Dark nebulae are so dense that they are opaque. Emission nebulae, or h ii regions, are glowing, ionized clouds of gas. ~ they appear as dark blots against a background of distant stars. Star formation begins in dense, cold nebulae, where gravitational attraction causes a. As a protostar grows by gravitational accretion of gases, kelvin-helmholtz contraction clump of material to condense into a protostar causes it to heat and begin glowing.
