The Fate of the Solar System Determined by the Sun

• Hydrogen is burned into helium in the core via nuclear fusion • Burning spreads to a shell on the edge of the core as hydrogen in the core is exhausted • Outer layers pushed away; Sun expands • Mercury, Venus, and likely Earth engulfed Red Giant

• Radius reaches 1-2 AU • Surface temperature drops to 2600 K Red Giant Red Giant

• Thousands of mes more luminous • Lower temperature gives red color • Mass loss through strong solar wind • Planets moved outward • Habitable zone moves towards Jupiter or Saturn Helium Burning

• Core is increasing in size and temperature • Reaches 108 K – can burn helium • Helium fusion begins, creates carbon + oxygen • Sun contracts to ~10 mes inial size • Now a horizontal branch star • Helium runs out quickly Asymptoc Giant Branch Star Asymptoc Giant Branch Star

• Outer layers pushed away, expands again • Fusion does not ignite in the core • Instead of contracng again, envelope is completely shed • Expands out in a planetary nebula Planetary Nebula

Ring Nebula. Hubble. Planetary Nebulae

Cat’s Eye Nebula (X-Ray) Eskimo Nebula. NASA. Planetary Nebula Necklace Nebula

Bright, dense regions in the gas envelope glow due to absorbed ultraviolet radiaon. Helix Nebula. IRAC. Helix Nebula. NASA. Emerging Planetary Nebula

• Felt as a strong solar wind • Likely to strip atmospheres • Does not completely destroy planets • Eventually a couple of light years across Core Collapse

• Not hot enough for fusion, so gravity “wins” • Carbon and oxygen core collapses unl degeneracy pressure takes over • Quantum effect, stops collapse • Now a small, dense, and hot ball of carbon and oxygen: a white dwarf White Dwarf

• Hot: Surface temperature is ~104 Kelvin • Dense: ~ 106 g/cm3 (Sun is 1.4) • Small: Size of a terrestrial planet

• Strong magnec fields, some over 106 Gauss White Dwarf

• No source of energy • Slowly cools as it radiates its heat away • Grows dimmer and eventually fades away on mescales of trillions of years • Some crystalline structure developed • Surviving planets freeze over