1	Astr 1050 Wed. Mar. 10, 2004 Today: Review HW if necessary End Ch. 11: Neutron Stars, Black Holes Review topics if time
2	Black Holes -- basics Nothing can stop collapse after neutron pressure fails Escape velocity from a surface at radius R: As R shrinks (but M is fixed), V_escape gets larger and larger At some point V_Escape= c (speed of light) Happens at Schwarzschild radius: Not even light can escape from within this radius
3	Examples: The Schwarzschild Radius: Mass in solar masses R_s (km) 10 3 2 1 0.000003 (Earth)
4	Examples: The Schwarzschild Radius: Mass in solar masses R_s (km) 10 30 3 9 2 6 1 3 0.000003 (Earth) 0.9 cm
5	Black Holes -- details Remember – gravity is same as before, away from mass Black holes do NOT necessarily pull all nearby material in A planet orbiting a new black hole would just keep on orbiting as before (assuming the ejected material or radiated energy didn’t have an effect) Any mass can potentially be made into a black hole – if you can compress it to a size smaller than R_S = 2GM/c² 1 M_Sun: 3.0 km 10⁶ M_Sun 3´10⁶ km 1 M_Earth 8.9 mm
6	Black Holes -- details If you do make material fall into a black hole, material will be falling at close to the speed of light when it reaches R_S If that falling gas collides with and heats other gas before it reaches R_S, then light from that hot material (outside R_S) can escape (important in quasars!).
7	Black Holes – detection By definition – can’t see light from black hole itself Can see large amounts of energy released by falling material just before it crosses R_S Can see motion of nearby objects caused by gravity of black hole
8	Black Holes – detection Example: Like White Dwarf accretion disk but w/ black hole instead Gas from red giant companion spills over towards black hole Gas spirals in toward black hole, through accretion disk Gas will be much hotter because it falls further, to very small R_S Gas will be moving at very high velocity Much faster than with white dwarf since much closer (P² µ a³) Signature of black hole: Very high energy release, very high velocity We find MASSIVE black holes in centers of most galaxies
9	Cygnus X-1
10	More Cool Stuff About Black Holes Time Dilation – originally “Frozen Stars” Gravitational Redshift Wicked Tidal Forces Hawking Radiation
11	Review Chapters 5-11 Chapter 5: Just a few topics Telescope resolution Function of size, wavelength Observations at different wavelengths
12	Review Chapters 5-11 Chapter 6: Starlight and Atoms Model Atom, parts, energy levels Emission and Absorption Lines Blackbody Radiation Wien’s Law, Steffan-Boltzmann Law Spectra of Stars Balmer thermometer, spectral types (OBAFGKM) Doppler Effect
13	Review Chapters 5-11 Chapter 7: The Sun Atmospheric Structure Temperature, density, etc., with radius Sunspots/Magnetic Phenomena What are they? Why do they exist? Nuclear Fusion – proton-proton chain What is it? How does it produce energy? Solar Neutrino “Problem” What is it? Is it still a problem?
14	Review Chapters 5-11 Chapter 7: The Sun – example question Q. The fusion process in the sun, the "proton-proton" chain, requires high temperatures because: c of the ground-state energy of the Hydrogen atom. c of the presence of Helium atoms. c the colliding protons need high energy to overcome the Coulomb barrier. c of the need for low density. c the neutrinos carry more energy away than the reaction produces.
15	Review Chapters 5-11 Chapter 8: The Properties of Stars Distances to Stars Parallax and Parsecs Spectroscopic Parallax Intrinsic Brightness: Luminosity Absolute Magnitude Luminosity, Radius, and Temperature Hertzsprung-Russell (H-R) Diagram Luminosity Classes (e.g., Main Sequence, giant) Masses of Stars Binary Stars and Kepler’s Law Mass-Luminosity Relationship
16	Review Chapters 5-11 Chapter 8: Properties of Stars—example question Q. A star’s luminosity depends only on the star’s: c distance and diameter. c temperature and distance. c distance. c temperature and diameter. c apparent magnitude Another version of the question can be made for apparent magnitude .
17	Review Chapters 5-11 Ch. 9: The Formation & Structure of Stars Interstellar Medium Types of Nebulae (emission, reflection, dark) Interstellar Reddening from dust Star formation Protostar Evolution on H-R Diagram Fusion (CNO cycle, etc.) Pressure-Temperature “Thermostat” Stellar Structure (hydrostatic equilibrium, etc.) Convection, radiation, and opacity Stellar Lifetimes
18	Review Chapters 5-11 Ch. 10: The Deaths of Stars Evolution off the main sequence (=> giant) Star Cluster Evolution on H-R Diagram Degenerate Matter Planetary Nebulae and White Dwarfs Binary Star Evolution (Disks, Novae, etc.) Massive Star Evolution and Supernovae
19	Review Chapters 5-11 Ch. 10: The Deaths of Stars—example question Q. Massive stars cannot generate energy through iron fusion because: c iron fusion requires very high densities. c stars contain very little iron. c no star can get high enough for iron fusion. c iron is the most tightly bound of all nuclei. c massive stars go supernova before they create an iron core.
20	Chapter 11: Neutron Stars & Black Holes Neutron Stars Pulsars (Radio pulsation, lighthouse model) Properties (size, density, composition) Black holes Schwarzschild Radius Properties Detection (Gravity, X-rays from Disks)