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Transcript
Stellar Evolution Part 2 The fate of the Sun Stars like our Sun Stars with masses similar to our Sun fuse at a rate that allows them to “live” as mainsequence stars for about 10 billion years. Then they run out of Hydrogen in their core Hydrostatic Equilibrium is lost… They Shrink a bit And begin to fuse Hydrogen into Helium in a shell outside the core. This Fusion generates more nuclear force than before. Hydrostatic Equilibrium is lost again… and they grow until they reach a new Hydrostatic equilibrium. The heat is spread over a larger surface area So it becomes cooler, leaving the main sequence to become… A Red Giant Which it will be for 80 million years! The Helium Flash Eventually the Core super-heats Becoming hot enough to start fusing Helium into Carbon all of a sudden The Helium Flash This raises the temperature of the star and makes it a Yellow Giant. But it is no longer stable And moves into the “instability strip” with its size and luminosity changing A Pulsating Yellow Giant Which it will be for about 100 million years The Sun becomes a Supergiant and dies When the Sun like star starts to run out of helium its fusion slows and the core shrinks. This briefly speeds up fusion The Star expands… and cools Becoming a Red Supergiant for about 15 million years. In the cool outer layers flakes of Carbon and Silicon form They are blown away by photons from the Core taking the outer layers of gas with them forming a … Planetary Nebula So called because through a small telescope they look like a planet. They have nothing to do with planets! They spread out disappearing after about 10,000 years The ‘Ant nebula” The Ant nebula is a side view of a planetary nebula The End of a Sun-like Star The bare hot core of the star that is left behind becomes a white dwarf that fades slowly into a black dwarf
