Study Guide for Quiz 2: ---------------------- Stellar Structure & Evolution ----------------------------- Energy Generation in Stars Nuclear Fusion Energy Proton-Proton Chain CNO Cycle Hydrostatic Thermostat Energy Transport Radiation Convection Conduction Thermal Equilibrium The Main Sequence Burn Hydrogen into Helium in their cores. In Hydrostatic & Thermal Equilibrium Mass-Luminosity Relationship for M-S stars The Main Sequence is a Mass Sequence Lower M-S: M < 1.2 Msun Radiative cores & Convective envelopes Burn H via p-p chain Upper M-S: M > 1.2 Msun Convective cores & Radiative envelopes Burn H via CNO cycle Red Dwarfs: lowest mass M-S stars Fully convective Burn H via p-p chain Dependence of M-S Lifetime on stellar Mass. Larger Mass = Shorter Life. Typical lifetimes of O-stars, M-stars, & the Sun Minimum and Maximum masses of stars Brown Dwarfs (M < 0.08 Msun) Star Formation Raw material is giant clouds of molecular hydrogen Triggers of cloud collapse and fragmentation into clumps Stages of star formation: cloud fragmentation into clumps free-fall contraction of clumps Protostar stage: in hydrostatic equilibrium and energy generation via Kelvin-Helmholz (gravitational contraction) Reaching the main sequence when H fusion ignites fully and star achieves Thermal Equilibrium Stages of Evolution of Low Mass stars (M < 4 Msun) Main Sequence phase through H exhaustion in core He core formation & H shell burning Ascent of the Red Giant Branch Helium Flash & the Triple-Alpha Process Descent to the Horizontal Branch He core burning & H shell burning C-O core formation Asymptotic Giant Branch star He and H burning Shells Onset of instability Envelope Ejection & Formation of a Planetary Nebula Core evolves into a White Dwarf star Stages of Evolution of High Mass O & B Stars (M > 4 Msun) Stars with 4 < M < 8 Msun Burn Hydrogen, then Helium, then Carbon Blow off their envelope after exhaustion of Carbin Burning Core becomes an O-Ne-Mg White Dwarf Stars with M > 8 Msun Burn Hydrogen up through Carbon, Neon, Oxygen & Silicon Iron Core Formation & burning shells Catastrophic collapse of Iron Core leading to Iron core bounce & supernova explosion ejecting envelope core collapses to a neutron star or black hole Supernovae Nucleosynthesis in Supernovae (main source of heavy elements) Role of supernovae in seeding interstellar space with heavy elements Endpoints of Stellar Evolution ------------------------------ White Dwarfs: Remnant cores of low-mass stars (M < 8 Msun) Held up by Electron Degeneracy Pressure Maximum Mass ~1.4 Msun (Chandrasehkar Mass) White dwarf evolution into a "Black dwarf" Neutron Stars: Remnant cores of massive stars (M > 8 Msun) Held up by Neutron Degeneracy Pressure Pulsar = rapidly spinning neutron star Model for a pulsar Pulsar evolution Black Holes: Black Holes are totally collapsed objects gravity so strong not even light can escape predicted by General Relativity theory remnant cores of very massive stars (M > 18 Msun?) Schwarzschild Radius & Event Horizon Find them by their Gravity X-ray Binary Stars & Black Hole Candidates Hawking Radiation & Black Hole Evaporation Tests of Stellar Evolution -------------------------- H-R Diagrams of Star Clusters Why clusters are good for testing stellar evolution Changes in the H-R diagram of a star cluster as it ages Estimating cluster ages from the Main-Sequence Turn-off Open Clusters Young clusters of few 100s - 1000s of stars Blue Main-Sequence stars & few giants Shapes of their H-R diagrams Range of ages from Few million to few billion years Globular Clusters Old clusters of a few 100,000 stars No blue Main-Sequence stars & many giants Shapes of their H-R diagrams 10-13 Billion years old