Exam 3 Review - Stellar Evolution PDF

Exam 3 Review material Stars can be divided into three main groups based on mass: - Low mass stars: < 2 solar masses - Intermediate mass stars: 2-8 solar masses - High mass stars: > 8 solar masses ### Mass and Stellar Lifetime - More massive stars have shorter lifetimes despite having more hydrogen...

Exam 3 Review material Stars can be divided into three main groups based on mass: - Low mass stars: < 2 solar masses - Intermediate mass stars: 2-8 solar masses - High mass stars: > 8 solar masses ### Mass and Stellar Lifetime - More massive stars have shorter lifetimes despite having more hydrogen to burn - Higher mass leads to greater luminosity and faster hydrogen burning rates - M stars (0.1 solar masses) have longer lifetimes than G stars (1 solar mass) and O stars (40 solar masses) ## Evolution of Low Mass Stars ### Red Giant Phase - Core hydrogen is depleted and converted to helium - Core contracts and heats up - Star expands and surface temperature decreases - Luminosity increases significantly - Outer layers begin to be driven off due to decreased surface gravity - Can lose up to 80% of mass during thermal pulses in double shell burning phase ### Planetary Nebula Formation - Outer layers form expanding shells of gas - Core becomes exposed as a hot, dense white dwarf - Core temperature around 100,000 K with spectrum peaking in ultraviolet - UV radiation keeps nebula hot and glowing - Different emission lines create varied colors in nebula ### White Dwarf Stage - Final stage for low mass stars - Composed of ultra-dense carbon - Cannot fuse carbon due to insufficient core temperature - Supported by electron degeneracy pressure - Based on quantum mechanical principles: - Heisenberg uncertainty principle - Pauli exclusion principle - Electrons must move rapidly when tightly packed, creating pressure ## Evolution of Intermediate and High Mass Stars ### Intermediate Mass Stars (2-8 solar masses) - Evolve off main sequence quickly - Become supergiants briefly - Achieve helium fusion more rapidly than low mass stars - End with carbon/oxygen core - Form white dwarfs after outer layers are ejected ### Massive Stars (>8 solar masses) - Develop onion-like shell structure through successive fusion stages - Each fusion stage becomes progressively shorter - Core fusion stops at iron - Iron fusion requires rather than releases energy - Core collapse leads to: - Electron-proton combination forming neutrons - Formation of neutron star or black hole - Supernova explosion ### Supernova Characteristics - Release more energy in an instant than Sun's entire lifetime - Energy released as: - Light - Neutrinos - Shock waves - Create and disperse heavy elements - Last observed Milky Way supernova was in 1604 ## Stellar Lifecycles Comparison ### Low Mass Stars (~billions of years total) 1. Main sequence (80%) 2. Red giant (18%) 3. Helium burning (1%) 4. Double shell burning (