Study Guide for Quiz 2: ----------------------------- Stellar Structure & Evolution ----------------------------- Energy Generation in Stars Hydrostatic equilibrium Nuclear Fusion Energy The Solar Age crisis Proton-Proton Chain Neutrinos CNO Cycle Hydrostatic Thermostat, thermal equilibrium Energy Transport: Radiation, Convection 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 Burn H via p-p chain Upper M-S: M > 1.2 Msun Burn H via CNO cycle Red/Brown Dwarfs: lowest mass M-S stars 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 t_MS ~ 1/M^3 Minimum and Maximum masses of stars Brown Dwarfs (M < 0.08 Msun) The 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 What are the timescales for these phases? Which way do stars move on the HR diagram? 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 What are the timescales for these burning phases? 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 we think BHs come from stars with M > 20-30 Msun Supernovae Nucleosynthesis in Supernovae (main source of heavy elements) Role of supernovae in seeding interstellar space with heavy elements Role of supernovae in producing neutron stars Star formation & the main sequence raw material for stars are giant molecular clouds cold and dense blobs of gas in galaxies steps in star formation: gravitational collapse establish hydrostatic equilibrium (proto-star phase) establish thermal equilibrium (pre-main sequence phase) land on the main sequence planets-forming debris disks around newly formed stars what energy source powers a protostar? what is the Kelvin-Helmholz timescale? which stars reach the main sequence the fastest? are low or high-mass stars intrinsically rarer? what are the minimum and maximum masses of stars? White Dwarfs: Remnant cores of low-mass stars (M < 8 Msun) About the size of the Earth R ~ 5000 km Held up by Electron Degeneracy Pressure Different from the Ideal Gas Law Equation of State Maximum Mass ~1.4 Msun (Chandrasehkar Mass) White dwarf just cools off over a long time. Can accrete from a binary companion, or run into another white dwarf to produce a Type Ia supernova; thermonuclear detonation; run-away C burning. Produces a lot of Iron, most of the Iron in the universe. Neutron Stars: Remnant cores of massive stars (M > 8 Msun) About the size of a city: R ~ 10 km. Held up by Neutron Degeneracy Pressure Pulsar = rapidly spinning neutron star Neutron stars cannot support themselves above 2-3 Msun. Neutron degeneracy pressure fails. Gravity wins. Black hole formation 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 > 20-30 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 Cosmic Distances: Trigonometric Parallaxes RR Lyrae Variables Cepheid Variables Period-Luminosity Relation The Milky Way Galaxy -------------------- The Milky Way is our Galaxy Diffuse band of light crossing the sky Galileo: Milky Way consists of many faint stars The Nature of the Milky Way Philosophical Speculations: Wright & Kant What is the geometry of the Milky Way? A spherical shell, or a disk? Size of the MW from Star Counts: Herschels Star Gauges Kapteyn Model Globular Cluster Distribution: Shapley, RR Lyrae stars First to locate the Sun outside the center of the Galaxy. The importance of dust obscuration in calculating the luminosity distance. Nature of the "Spiral Nebulae" ------------------------------ Two hypotheses: spiral nebulae are external, or internal to Milky Way? Island Universe Hypothesis (Kant & Humboldt) Nebular Hypothesis (Laplace) Role of finding distances in resolving the debate Leavitt: Cepheid Period-Luminosity Relation, distances Shapley-Curtis Debate (1920) Hubble: Cepheids in Andromeda The Milky Way & Andromeda ------------------------- Common Properties of the Milky Way & Andromeda Galaxies Disk & Spheroid Structure of the Galaxy Pop I Stars: Young, metal-rich, disk stars Ordered, nearly circular orbits in the disk Pop II Stars: Old, metal-poor, spheroid stars Disordered, elliptical orbits in all directions Chemical Evolution, connection to stellar populations Supermassive Blackholes