ASTR 103 Lecture Notes - Lecture 15: Asymptotic Giant Branch, Supernova Remnant, Planetary Nebula
Document Summary
Low-mass stars go through two distinct red-giant stages. ~ a red giant when shell hydrogen fusion begins. ~ a horizontal-branch star when core helium fusion begins. Bringing the products of nuclear fusion to a giant star"s surface. As a low-mass star ages, convection occurs over a larger portion of its volume. Low-mass stars die by gently ejecting their outer layers, creating planetary nebulae. Helium shell flashes in an old, low-mass star produce thermal pulses during which more. Ultraviolet radiation from the exposed core ionizes and excites the ejected gases, than half the star"s mass may be ejected into space. This exposes the hot carbon-oxygen core of the star producing a planetary nebula. The burned-out core of a low-mass star cools and contracts until it becomes a white. No further nuclear reactions take place within the exposed core. Instead, it becomes a degenerate, dense sphere about the size of the earth and is called a white dwarf.
