ASTRONOMY 1020
STELLAR AND GALACTIC ASTRONOMY
OUTLINE OF COURSE OF STUDY


 

THE NATURE OF LIGHT & MATTER

Prologue:  The Known Universe - this video journey, produced by the American Museum of Natural History touches on every single topic contained in this on-line outline of the Astronomy 1020 lecture & lab.

 

The short video above is based on the classic Powers of Ten short film by Charles & Ray Eames (1977):

 

I.  The Interaction of Light and Matter

A. Properties of Waves, from Slinky Coils to the Vacuum of Space

1.  waves transmit energy from one place to another via a propagating disturbance
2.  mechanical waves propagate through a medium
3.  properties of waves
a.  amplitude of wave (magnitude of disturbance)
b.  velocity of wave (speed of propagation of the disturbance)
c.  wavelength of wave (distance between peaks of the disturbance)
d.  frequency of wave (number of peaks which pass a point per unit time (units:  1 cycle/sec = 1 hertz)
4.  fundamental wave equation:  velocity of wave = wavelength x frequency (v = λf)
5.  electromagnetic waves:  disturbance in the electric and magnetic fields surrounding an accelerating (or changing) charge which propagates through the vacuum of space at 3 x 108 meters/second (light is an electromagnetic wave, so this speed is called the "speed of light", symbolized by the letter "c")
a.  electric and magnetic fields are oriented perpendicular to the direction of propagation:  E&M waves are transverse waves
b.  the electromagnetic spectrum:  (high frequency, short wavelength)  ------>  (low frequency, long wavelength)
gamma rays, X-rays, ultraviolet, visible, infrared, submillimeter ("terahertz radiation"), millimeter, mircowave, VHF, FM radio, AM radio

B.  Kirchhoff's Laws & Cavity Radiation

1.   Kirchhoff's Laws: The Interaction of Light and Matter
a.  the term "line spectra" comes from a common design of spectrographs in which the entrance aperture (located at the focal plane of a telescope or lens) had the shape of a narrow slit which produced spectra consisting of projected images of the slit (lines) offset by color (wavelength)
b.  Kirchhoff's laws:  a set of empirical laws describing the three main types of spectra and the state or physical characteristics of the matter that radiates those spectra
i. continuous spectra (cavity radiation):  emitted by hot solid (or hot plasma)
ii. absorption line spectra (dark line):  caused by low density cool gas absorbing light from an underlying continuous spectra source
iii. emission line spectra (bright line):  emitted by low density hot gas
2.  Cavity Radiation = Black Body Radiation
a.  black body radiator = perfect or ideal thermal radiator
b.  The closest set-up in the lab to a perfect absorber/radiator is a small hole which extends into an irregular cavity in a metal material; radiation from the cavity, emitted through the hole, will closely approximate a perfect thermal continuous spectrum = black body spectrum; this was also known as cavity radiation
a.  cavity or black body radiation is continuous over the entire E&M spectrum starting with zero intensity at zero wavelength, rising to a peak intensity, then the intensity approaches zero again as the wavelength approaches infinity
b.  the wavelength at which the peak in the spectrum occurs is inversly proportional to the absolute temperature, and the total power per unit area emitted (the intensity summed over the entire spectrum) is directly proportional to the absolute temperature to the forth power
c.  Wien's law:  describes the temperature dependance of the wavelength of the peak in the black body spectrum: 

                            λmax = constant/T
d.  Stefan-Boltzmann law:  describes the temperature dependance of the total radiated power per unit area of the black body (intensity summed over the entire E&M spectrum):

                                                                    P/A = σT4

                            

C.  Blackbody Radiation and the Ultraviolet Catastrophe

1.  the ultraviolet catastrophe:  when classical E&M theory is used to calculate the form of a black body spectrum (assumes light is emitted by oscillators with a continuous energy range) it fits the observations at longer wavelengths, however it diverges exponentally from the observed spectrum at short wavelengths and predicts the non-sensical result that as the wavelength approaches zero the intensity approaches infinity!
2. the Plank curve:  Plank's idea of constraining the oscillator energies to discrete values (later called quantizing the energies) was one of the first steps in the road to the theory now known as quantum mechanics or quantum theory

D.  Quantum Mechanics and Atomic Structure

1. the quantization of light and atoms
a.  Rutherford-Bohr atomic model:  the "solar system" model of the atom
i.  Rutherford determined though scattering experiments that the atom must consist of a very small, positively charged, comparitively massive nucleus orbited by light weight electrons of negitive charge
ii.  classical theory predicted that the Rutherford atom would be unstable; by quantizing the angular momentum (and energy) of the electron orbits, Bohr produced a stable model of the atom and explained the wavelengths of the line spectra of hydrogen
b.  Einstein and the photoelectric effect:  while Einstein was never completely confortable with quantum theory, he won a Nobel Prize for his work explaining the photoelectric effect by treating light as "particles" and became in effect one of the founding fathers of quantum theory;  these "particles" of light energy are called photons and their energy is proportional to their frequency:  Ephoton = hf, h = Planck's constant, f = frequency;  (using the basic wave equation this can also be written in terms of wavelength:  Ephoton = hc/λ )
c.  The interaction of photons with electrons in different energy levels (orbits) of an atom explain the origin of absorption and emission spectra; click here for a link to an interactive animated model of how line spectra arise
2. the wave-particle duality of nature:  the particle-like nature of light - photons (Einstein); the wave-like nature of particles - deBroglie waves (deBroglie); these ideas led to one of the fundamental principles of quantum theory:  all matter and energy can only be described as a wave in some situations and only as particles in other situations (but not both at once); this is called the wave-particle duality of nature

See a short time-line of the development of Quantum Mechanics - here.

II. Optics, Telescopes and Instrumentation

A. Optical telescopes

1.  simple thin lenses:  converging lens optics
a. converging lens optical definitions:  focal point, focal length
b. two cases of conveging lens optics:  real inverted images, virtual erect images
2.  principle: objective lens/mirror focuses inverted real image of object, eyepiece magnifies real image
a. refracting telescopes: uses lenses
b. reflecting telescopes: uses mirrors
c. catadioptric telescopes: combination of lenses, mirrors
3.  3 functions of telescopes
a. magnification – applies primarily to telescopes used for visual observation: value of the angular magnification of a telescope = fobj/feye, fobj = focal length of objective lens/mirror, feye = focal length of eyepiece
b. resolution – ability to discriminate fine detail, optics limit determined by the diameter of the objective lens, but Earth’s atmosphere usually limits the resolution of ground bases telescopes
c. light-gathering power – ability to collect light and reveal fainter details, determined by the area of the objective lens/mirror (assuming a circular lens/mirror, then area proportional to the diameter squared) or mirror
4.  adaptive optics systems: the distortions caused by atmospheric turbulence can be measured and corrected by a flexible mirror in real time to overcome the resolution limit due to the atmosphere
5.  light pollution: for astronomers the unnecessary sky glow caused by poorly designed urban lighting is considered the main component of light pollution.  However, other aspects of this problem impact all of our lives:  glare, light trespass, trashy looking and confusing nighttime environments, and energy waste are some of the ways light pollution manifests itself.

B. Instrumentation

1. CCD camera systems
2. spectrographs

C. Other telescope types

1. radio telescopes
2. Earth-orbiting telescopes

 

MEASURING PROPERTIES OF STARS

III. The Nature of Stars (Measuring the Properties of Stars)

A. Stellar distances and velocities

1. stellar parallax:  determining stellar distances (1st step in the cosmic distance scale)
2. proper motion & transverse velocity:  proper motion - angular velocity across the sky; transverse velocity - proper motion and stellar distance combine to give the stellar velocity perpendicular to the line of sight to the star
3. radial velocity:  measuring the doppler shift gives the line of sight velocity of a star
4. space velocity relative to the Sun:  the velocity of a star through space relative to the Sun can be determined from the distance + proper motion (transverse velocity) and the radial velocity (line of sight velocity)

B. Magnitude scales 

1. apparent magnitude
2. absolute magnitude and luminosity

C. Star colors and surface temperatures

D. Stellar spectral classification

E. The Hertzsprung-Russell diagram
(Click here for HR Diagram graphic with magnitude & spectral type definitions and history.)

F. Luminosity Classes

G. Binary stars and stellar masses

1. binary star types
2. eclipsing-spectroscopic binaries

IV. Our Star, The Sun  (link:  http://solar.physics.montana.edu/YPOP/, a solar physics edu. site)

A.  Modeling the Sun:  How Do We Determine the Structure and Evolution of Stars?

1.  the "physics" of stars:  the equations & numerical models of stellar structure represent the known physics needed to determine the interior structure of a star and to predict its overall surface properties over time (stellar evolution); the balance between gravity (pulling the star's mass together) and pressure (pushing it apart) can be thought of as the main physical effect that determines the final structure and surface properties of a star.  This effect is described primarily by the equation for hydrostatic equilibrium.  However, the equation of hydrostatic equilibrium is only one of four interconnected equations that are used for modeling the interior and surface properties of stars.
  • a.  Hydrostatic equilibrium:  describes the "contest" between gravity and pressure which ultimately determines the star's structure
    b.  Conservation/continuity of mass:  describes the mass as a function of radius and relates the mass and its associated gravity forces
    c.  Energy transport (either via radiation, or convection - convection needing a semi-empirical treatment):  describes how energy is transported throughout the structure of the star
    d.  Energy generation through nucleosynthesis or gravitational contraction:  describes the fusion reactions that provide the energy generation  which maintains pressure against gravity or the conversion of gravitational energy into heat energy that occurs mostly during the pre-MS stages of a star's life

     

     






















    2.  computer modeling can determine the interior structure and surface properties of stars by solving (integrating) the above equations simultaneously; it also describes the changes in a star's interior structure and surface properties over time (stellar evolution); early models were "one dimensional" - all equations were written only as a function of radius; more realistic models using 2-D or 3-D modeling techniques can more fully take into account the energy transport via convection rather than using the semi-empirical approximation of 1-D models
    Link to a shockwave app that lets you graphically evolve different mass stars:   Watch stars evolve across the HR diagram 
    Link to an on-line version of the computer models referred to above, submit mass, composition & 2 parameters concerning convection to compute the interior structure of a ZAMS star:  Michael Briley's "The Stellar Interior Construction Site" (unfortunately, this site seems to be permanently disabled)
    •

    B. The Internal and Surface Structure of the Sun

    1. internal structure:  core, radiative zone, convective zone
    2. energy production in the core
    a. proton-proton chain
    b. CNO cycle
    3. photosphere: the solar "surface"  (Note:  This links to the most recent pair of solar images used in the solar rotation lab.  Note the limb darkening and the sunspot motion during the time interval between the image pair due to solar rotation, rot. period = 27 days at the equator.)
    a.  sunspot cycle:  11 year solar activity cycle, number of sunspots peak every 11 years (more sunspots = more activity)
    b.  the solar magnetic cycle:  the solar magnetic field reverses every 11 years, returning to its original state every 22 years (one complete solar magnetic cycle = 22 years)
    4. Probing the interior of the Sun
    a. solar neutrinos
    b. solar seismology

    C.  The Solar "Atmosphere" and the Solar Wind (solar atmosphere diagram)solar atmosphere diagram

    1.  chromosphere (~10,000 kelvin)           
    2.  hot corona (~106 kelvin)
    3.  solar wind:  stream of particles (electrons and hydrogen nuclei) accelerated out of the corona, reaches speeds in excess of 1,000,000 miles an hour

    An intense "reconnection" event causes a massive
    Solar Flare in this you-tube video:

     

    Click here for a more recent video of a solar flare and the formation of a sunspot group.

     

     

    STELLAR EVOLUTION
    (Click here for low and high mass stellar evolutionary track diagrams.)
     

    V. The Interstellar Medium and the Life Cycle of Stars

    A. The interstellar medium and star formation

    1. neutral atomic hydrogen (HI):  warm diffuse atomic gas (WDAG); cold atomic clouds (CAC)
    a.  temp: 50 K (CAC); 5000 K (WDAG)
    b.  density: 10-20 atoms/cm3(CAC); 0.1 atoms/cm3(WDAG)
    c.  size:  ~30 ly diameter (CAC); not in discrete clouds (WDAG)
    d.  mass:  103 solar masses (CAC); not in discrete clouds (WCAG)
    e.  pressure equilibrium:  P(CAC) = P(WDAG) = P(coronal gas)
    f.  relative volume (CAC + WDAG):  ~50% total ISM
    g.  relative mass (CAC + WDAG):  ~50% total ISM
    2. giant molecular clouds (H2)
    a.  temp: ~10 K
    b.  density: 1000 - 10,000  molecules/cm3
    c.  size:  ~5--100 ly diameter
    d.  mass:  106 solar masses
    e.  self gravitating:  gravity > pressure
    f.  relative volume:  ~1% total ISM
    g.  relative mass:  ~50% total ISM
    3. HII regions (ionized hydrogen), linked image is the Orion Nebula as imaged at NGAO
    a.  temp: ~104 K
    b.  density: 100 - 1000  ions/cm3
    c.  size:  ~10 ly diameter, small "blisters" on side of molecular clouds
    d.  mass:  negligible
    e.  self gravitating:  pressure > gravity (disperse in ~million years)
    f.  relative volume:  ~0% total ISM
    g.  relative mass:  ~0% total ISM
    4. coronal gas (super bubbles), created by supernova explosions,  shock waves, (sometimes superbubbles from many SN combine and burst out of the disk as in the linked image)
    a.  temp: ~1,000,000 K
    b.  density: 0.001  ions/cm3
    c.  size:  large, creates "superbubbles", sponge-like ISM
    d.  mass:  negligible
    e.   pressure equilibrium:  P(CAC) = P(WDAG) = P(coronal gas)
    f.  relative volume:  ~50% total ISM
    g.  relative mass:  ~0% total ISM

    B.  Stellar Life-Cycle Overview in Relation to the ISM  (Refer to the above 4 panel figure diagramming the 4 regions of the ISM)

    1.  Panel 1:  Stars form in Giant Molecular Clouds, in this panel star formation has just been initiated in one part of the molecular cloud (located roughly in the center of the panel).  Something (see panel 3) initiates the formation by causing the molecular cloud's density (at least in one part of the cloud) to exceed the critical density such that gravity begins to overcome pressure and a several 1000 solar mass cloud begins collapsing and sub-fragmenting, resulting in the formation of a cluster of stars.  (See next panel.)

    2.  Panel 2:  A cluster of stars has formed on the edge of the molecular cloud and massive stars within the cluster carve out a region of ionized hydrogen called an HII region.  This HII region "bubble of ionized gas" presses on the "parent" molecular cloud which initiates more star formation in the cloud.  (See panel 3.)

    3.  Panel 3:  One or more of the most massive stars in the star cluster has exploded as a supernova which creates a "bubble" of very, very hot ionized gas around the exploding star called a Coronal Gas region, sometimes called a "super bubble" if very large.  The shock wave from the supernova initiates more star formation in the molecular cloud.  The supernovae and HII regions create a "domino" effect of star formation in the molecular cloud.

    4.  Panel 4:  The molecular cloud has been "used up" producing many star clusters.  These stars (especially the more massive stars) blow material created in their interiors by stellar nucleosynthesis back into the interstellar medium.  In this way the ISM is enhanced in elements heavier than Helium.  Later generations of stars then have greater abundances of heavy elements as the cycle of stellar birth begins again.

    VI.  The Stages of Stellar Evolution

    A. Protostars

    1. Jean's theory & gravitational collapse
    2. dark nebulae and protostars
    a. Bok globules
    b. evolutionary tracks
    c. brown dwarfs
    d. cocoon nebula

    B. Pre-main-sequence stars

    1. T Tauri stars
    a. protoplanetary disks
    b. polar outflow (bipolar jetting)
    c. Herbig-Haro objects
    2. stellar winds (hot massive stars)

    C. Leaving the main sequence

    1. main sequence lifetimes
    2. shell "burning"

    D. Star cluster evolution

    1. clusters as probes of stellar evolution
    a. all stars in a cluster are at the distance from Earth
    b. all stars in a cluster are the same age
    c. range of masses, evolve at different rates
    2. cluster main sequence
    a. ZAMS
    b. turnoff point
    3. cluster types
    a. young, "metal-rich" clusters
    i. OB associations
    ii. open clusters

    b. old, "metal-poor" globular clusters

    E. Red giants

    1. low mass stars evolutionary tracks
    a. degenerate core
    i. Pauli exclusion principle
    ii. degenerate electron pressure
    b. core helium burning
    i. helium "flash"
    ii. triple alpha process
    c. post-helium-flash evolution
    i. stellar structure readjusts
    ii. horizontal branch
    2. high mass stars evolutionary tracks
    a. core helium burning
    i. smooth onset (non-degenerate core)
    ii. peak luminosity
    b. HR diagram "loops"
    3. mass loss from giant stars
    a. stellar winds
    b. Wolf-Rayet stars

    F. Stellar pulsations

    1. long-period variables
    2. instability strip pulsating stars
    a. RR Lyrae variables
    b. Cepheid variables

    G. The evolution of binary stars

    1. mass transfer
    2. blue stragglers

    H. AGB stars and planetary nebulae

    1. shell helium burning
    a. red supergiant
    b. asymptotic giant branch
    2. thermal pulses
    3. planetary nebulae

    I. White dwarfs

    1. degenerate electron pressure
    2. mass-radius relation and the Chandrasekhar limit
    3. black dwarfs

    J. High mass stars and heavy element synthesis

    1. nucleosynthesis in massive stars
    a. hydrogen -> helium
    b. helium -> carbon, oxygen
    c. carbon -> neon, magnesium, oxygen, helium
    d. neon -> oxygen, magnesium
    e. oxygen -> sulfur, silicon, phosphorus, magnesium
    f. silicon -> iron
    2. s and r processes
    a. s processes (slow neutron capture)
    b. r processes (rapid neutron capture)

    K. Supernovae (Type II)

    1. single star progenitor with iron core
    2. core collapse
    a. photodisintegration
    b. inverse beta decay
    i. intense neutrino pulse
    ii. degenerate neutron core
    3. core bounce shock wave
    a. turbulent shock front
    b. neutrinos interact with shock wave
    4. supernova explosion results
    a. neutron star
    b. total disruption
    c. black hole
    5. type characteristics
    a. hydrogen in spectra
    b. single star progenitor
    c. powered by gravitational energy

    L. Supernovae (Type Ia)

    1. semidetached binary progenitor
    a. carbon-oxygen white dwarf
    b. red giant companion
    2. mass transfer to white dwarf
    a. mass builds to 1.4 Mu
    b. catastrophic carbon burning
    i. detonation (burn-wave faster than sound)
    ii. deflagration (burn-wave slower than sound)
    3. supernova explosion results
    a. neutron star
    b. total disruption
    4. type characteristics
    a. no hydrogen or helium in spectra
    b. binary star progenitor
    c. powered by nuclear energy (we're talkin' star-sized nuclear bomb here...)

    M. Supernovae (Type Ib) (Lecture)

    1. single star progenitor with iron core
    2. outer hydrogen layer lost by intense stellar wind (Wolf-Rayet star)
    3. type II supernovae mechanism for explosion with same results
    4. type characteristics
    a. no hydrogen in spectra, but rich in helium
    b. single star progenitor
    c. powered by gravitational energy

    N. White dwarfs, black dwarfs

    O. Neutron stars

    1. pulsars and neutron stars
    a. discovery (LGMs)
    b. nature of pulsars
    2. properties of neutron stars
    a. density
    b. spin
    c. magnetic field
    3. energy loss and period lengthening
    4. interior of neutron stars
    5. millisecond pulsars
    a. spin-up by a binary companion
    b. the Black Widow Pulsar
    c. precise clocks and planetary systems
    6. neutron stars in binary systems
    a. pulsating X-ray sources
    b. bipolar jets
    c. novae (WD) and bursters (neutron star)

    P. Black holes

    1. definition
    a. massive core > 2.5 - 3 Mu
    b. escape velocity > c
    2. special and general relativity
    a. special relativity
    i. time dilation
    ii. Lorentz-Fitzgerald contraction
    iii. relativistic momentum
    b. general relativity
    i. principle of equivalence
    ii. space-time curvature
    3. "black holes have no hair"
    a. structure
    i. center singularity
    ii. event horizon
    b. mass, charge, and spin
    4. gravitational lens
    5. black hole candidates
    a. binary systems
    b. accretion disks and X-ray emission
         Next Section

     

    GALAXIES, GALAXY SYSTEMS

    VII.Our Galaxy

    A. The structure of the galaxy

    1. location of the Sun and the shape and size of the galaxy
    a. early measurements: the disk
    i. "star gauging"
    ii. affect of dust
    b. Shapley and the distribution of globular clusters: the spheroidal component (halo, nuclearl bulge)
    i. the direction to the galactic nucleus and galactic coordinates
    ii. the distance to the center and the size of the galaxy
    c. the solar neighborhood
    i. our position in the disk
    ii. the local superbubble
    2. spiral structure
    a. stellar populations
    b. spiral arm tracers
    i. stellar associations and young clusters
    ii. radio techniques: HI & CO2

    B. The Sun's orbit about the galactic center

    1. the Sun's direction of travel
    2. estimating the mass inside the Sun's orbit
    3. estimating the mass of the whole galaxy


















    C. Spiral arm formation                                                   (M33 visible light = red, radio [HI] = blue) 

    1. flocculent spiral galaxies
    a. self-propagating star formation
    b. differential rotation
    2. grand-design spiral galaxies
    a. density wave theory  [Use GalCrash to make your own density waves!  Go to the GalCrash link below and run the applet.  In the control panel input the following initial conditions:  all angles (red, green theta; red, green phi) = 0; Peri (kpc) = 25.0; Red Galaxy Mass = 1.0 (ie. same mass as green galaxy); Number of Stars = 2000 (this is max no.);  check the Green Centered box and the Big Halos box, leave the Friction box blank.  Now start the simulation and watch as the close pass of the red galaxy causes spiral density waves to form in the green galaxy.  Note how the spiral density waves keep their shape and only slowly change as the stars (white dots) orbit around the galaxy's disk continously.]
    b. stellar orbits and epicycles
    c. shock waves and star formation
    d. density wave "drivers"

    D. Galactic nucleus

    1. visual observations
    a. estimated brightness
    b. completely obscured by dust
    2. radio and IR observations
    a. a look through the dust
    b. heated dust and synchrotron radiation
    3. galactic nucleus "zoom"
    a. star forming regions and dust streamers
    b. the "expanding arms"
    c. Sagittarius A
    i. gas filaments and magnetic field lines
    ii. the "pinwheel"
    iii. the molecular gas ring
    iv. stellar number density
    v. Sagittarius A*: supermassive black hole?

    VIII. Galaxies Upon Galaxies

    A. Properties of galaxies

    1. the distance to galaxies
    a. Shapley-Curtis debate
    b. Cepheid variable stars
    2. Hubble classification scheme (tuning fork diagram):
    a. elliptical
    b. barred spirals
    c. normal spirals
    d. irregulars

    B. Hubble redshift relation

    1. discovery
    2. modern measurements: This linked diagram shows the evolution of the measured value of the Hubble Constant from Hubble's first measurements through the beginning of the 1980's.  At that time the value seemed to partially converge to two possible values:  one around 100 km/s/Mpc and the other around 50 km/s/Mpc.  With the launch of the HST, a project to precisely determine the value of the Hubble Constant was begun.  By 1999 the results from the HST were in and the Hubble Constant had satisfyingly converged to a single value in-between the two earlier possibilities.  (See 2.b below.)
    a. standard candles:  Note that with the HST, the SN Ia standard candle can be directly calibrated by using the Cepheid PL relation and several of the intermediate standard candles shown on the linked diagram can be skipped.  This allows a more accurate determination of Hubble's Constant.  (See 2.b below.)
    b. the value of H0:  the present value of Hubble's constant as constraned by the HST SN Ia project is 70 km/s/Mpc +/- 10 km/s/Mpc (a more recent determination using WMAP data [see next section] is consistent with this value and gives 71 +/- 4 km/s/Mpc).  Click here to see Hubble's original diagram, the HST Hubble Constant Project diagram, and an extended Hubble diagram that we will see again in the Cosmology Section.

    C. Hierarchy of galaxy clustering

    1. the ultimate address:  (...to illustrate the tendency of objects to cluster on scales ranging from human to universal)
    Dr. Joseph H. Jones    (a cluster of molecules)
    Physics Dept.    (a cluster of physicists)
    NGCSU    (a cluster of academic departments)
    Dahlonega, GA 30597   (a cluster of homes, businesses, & institutions), (a cluster of cities and towns)
    U.S.A., North America    (a cluster of states), (a cluster of countries)
    Western Hemisphere, Earth    (a cluster of continents), (two hemispheres)
    Solar System Sol, Ursa Major Group    (a cluster of planets around a star), (a cluster of stars)
    Carina-Cygnus Spiral Arm, Milky Way Galaxy    (a spiral arm of stars, gas & star clusters), (a vast stellar system with spiral arms in a disk)
    Local Group, Virgo Supercluster    (a small cluster of galaxies), (a large cluster of clusters of galaxies)
    Local Megastructure, Universe    (a large structure of clusters of clusters of galaxies), (a cluster of all the megastructures)
    Multiverse?????????    (a cluster of many universes?)
    2. missing mass or the dark matter problem
    a. kinematics of clusters
    b. gravitational lens and dark matter
    3. using the Hubble relation, the overall structure of the Universe can be measured:

    In the following simulation of the distribution of dark matter in the Universe, the structure closely models the visual structure as discerned from actual observations of the structure of the Universe measured using the Hubble relation (see figure below the video):
     

    Here is the inner portion of the observed 2dF Galaxy Redshift Survey:

    D. Galactic formation and evolution

    1. formation of spirals and elliptical
                  a. 1st stars form in large "clumps" resembling dwarf irregular galaxies (small "protogalaxies")
                  b. small protogalaxies fall together to form larger galaxies
                                 i. stars of small protogalaxies fall together to form spheroidal component with highly
                                elliptical orbits, random orbit inclinations; star formation ends in spheroidal component
                                 ii. gas/dust component of small protogalaxies merge together into a disk component
                                due to conservation of angular momentum; star formation continues in disk, density
                                waves develop into spiral arms
                 c. initial conditions determine galaxy type
                                i. high initial angular momentum, large initial mass (no.s of protogalaxies) --> barred spiral
                                ii. lower initial angular momentum, large initial mass --> normal spiral
                                iii. high or lower initial angular momentum, low initial mass --> gas/dust component
                                of small protogalaxies used up before forming disk,
                                no ongoing star formation = regular elliptical
    2. colliding galaxies
    a. starburst galaxies:  galaxy interactions can cause a tremendous burst of star formation as in M82
    b. galaxy mergers:
    i.  Univ. Hawaii galaxy merger MPEG movies.
    ii.  Case Western Reserve Univ. JAVA galaxy crash simulations.  Note: this links to the index of JAVA applets, run Galcrash or Cannibal.
    c. galactic cannibalism:  many types of galaxies may merge in a rich cluster of galaxies to form a giant elliptical galaxy (cd elliptical, cd = central dominant)
    3. Hubble telescope investigates galaxy formation

    See below a visualization of a computer simulation of the formation of a disk galaxy from small protogalaxies:  gas = green; young stars = blue; old stars = red

    IX. Active Galaxies and Quasars

    A. Discovery of active galaxies

    B. Quasars (quasi-stellar radio sources = "radio loud") and QSOs (quasi-stellar objects = "radio quite")

    1. discovery of quasars
    a. 3C 48
    i. Allan Sandage
    ii. star-like radio source
    b. 3C 273
    i. Maarten Schmidt
    ii. enormous redshift
    2. origin of redshifts
    a. relativistic redshifts
    b. Hubble's law and quasar distance
    i. closest: 800,000,000 ly
    ii. average distance, 3 billion ly
    3. properties of quasars
    a. extraordinarily luminous
    i. distance from Hubble relation (redshift) combined with measured apparent brightness indicates extreme power output
    ii. extreme power output hard to explain due to estimated size of power source (see below)
    b. nonthermal radiation indicates high magnetic field environments with high energy charged particles
    i. synchrotron radiation = continuous spectrum produced by high energy charged particles trapped in high strength magnetic fields
    ii. polarized = nonthermal processes as above generate polarized radiation
    c. Arp and discordant redshifts:  Arp skeptical of large distances due to extraordinary energy density of power source required by objects located at such distances; he tried to find "connections" between quasars and "foreground" galaxies, implying much closer quasar distances and eliminating the extreme power outputs needed if quasars were indeed at large distances;  most recent observations of quasars show them to be at the distances determined by the Hubble relation and therefore Arp's ideas have been rejected
    d. quasar "fuzz"; faint light surrounding some quasars, difficult for ground based telescopes to measure, has more recently been confirmed to be the surrounding "host galaxy" of the quasar = AGN
    i. host galaxies have been imaged by HST, confirming that quasars and QSOs are indeed very powerful distant AGNs.
    ii. recent Hubble results:  quasar host galaxies

    C. Seyfert galaxies and radio galaxies

    1. Seyfert galaxies
    a. resemble faint "radio quite" quasars (QSOs)
    b. compact nuclei with energetic activity
    2. radio galaxies
    a. resemble faint "radio loud" quasars
    b. bi-polar jets
    c. double radio sources (radio lobes)
    d. head-tail radio sources

    D. Active galactic nuclei (AGNs)

    1. Quasars, Radio Galaxies, and Seyfert Galaxies are all classified as AGNs
    a. all have very luminous galactic nuclei, variable on short time scales, & emit nonthermal radiation indicating a similar "central engine" or power source in the nuclei of these galaxies
    b. differences in total luminosity and viewing orientations explain the major differences between the AGN types
    2. AGNs in order of luminosity:  a. = most powerful ---> c. = least powerful
    a. quasars & qsos (,,,and  blazars = BL Lacertae objectst [see below])
    b.  radio galaxies
    c. Seyfert galaxies
    3. variability of sources
    a. limits size of light source:  variations in a given time interval indicate maximum size is the distance light can travel in that time interval
    b. fluctuations of AGNs can occur with time scales of "days" up to " about a year",  indicating light sources must be maximum of 1 ly across (approximate size of our solar system)
    4. AGN power source model   [schematic -> 
    a. supermassive black hole at the center of a thick accretion disk as the "central engine"
    i. Eddington limit = mass at which a normal star would blow apart from its own light pressure:  central engine cannot be a super-massive "normal" star
    ii. rotation curves of host galaxies near the galactic nuclei indicate millions to billions of solar masses in the galactic nuclei which along with the variability of the central power source (limit on volume of power source) indicate the presence of a super-massive black hole
    iii. stellar densities near galactic nuclei are consistent with a process of coalescing stars and stellar size black holes which would eventally form a super-massive black hole in the glactic nuclei
    b. thick accretion disk
    i. "centrifugal barrier" shock front:  as material spirals into the black hole, at the inner edge of the accretion disk where conservation of angular momentum causes the material to go fast enough to (almost) achieve a stable orbit around the central black hole a shock front forms causing the infalling material in the outer accretion disk to "pile up" at that point producing a thick donut shaped inner ring to the accretion disk
    ii. mass is expelled from the thin inner accretion disk by various processes (related to the vast rotational energy of the central black hole and tidal compression of material as it nears the black hole), this outflowing mass is directed into powerful bi-polar jets by the funnel shaped cavity created by shock front (thick donut shaped inner ring of the accretion disk) and also by magnetic fields associated with the rotating accretion disk "plasma"
    iii.extremely powerful relativistic jets are expelled from "poles" of accretion disk
    iv. jets "focused" by interstellar medium of host galaxy and by entrained magnetic fields
    c. angle viewed partially determines type of AGN we observe
    i. directly into jet -> blazar
    ii. close angle to jet -> quasar, type I Seyfert
    iii. close angle to plane of the accretion disk -> radio galaxy, type II Seyfert

     

    COSMOLOGY AND BEYOND

    X. Cosmology: Past, Present, Future of the Universe (click here for video-text comparison figure)

    A. Early scientific cosmologies and Olber's paradox

    1. a static, infinite universe
    2. "Why is the sky dark at night?"

    B. The expanding universe

    1. Hubble's law (rubber rulers & raisin bread)
    2. cosmological redshift verse doppler shift

    C. The big bang

    1. cosmological principle
    a. homogeneous
    b. isotropic
    2. running the "movie" backwards
    a. light horizon (cosmic particle horizon)
    b. Hubble age
    c. Olber's paradox revisited
    3. the initial singularity (the balloon model)
    a. Where was it?
    b. What's "outside" the universe?
    c. What happened before or at the moment of the Big Bang?
    i. Plank time
    ii. wave-particle duality

    D. Evidence of an expanding universe

    1. the Hubble law (redshifted galaxy clusters)
    2. the composition of the universe
    a. too much helium (25% by mass)
    b. early universe had to have conditions of temperature and density similar to the present core of the Sun
    3. the cosmic microwave background radiation (CBR for short)
    a. Penzias and Wilson, discovery
    b. Cosmic Background Explorer (COBE)
    i. very accurate measurement of the CBR spectrum
    ii. average temperature of the universe:  2.73 K
    iii. extremely isotropic after correction for our peculiar velocity
    iv. some extremely small fluctuations:  helps account for galaxy formation
    c. Radiation dominated early universe
    i. average density of matter is much greater than the average mass density of radiation at the present time -> matter dominated universe
    ii. 1 million years after the Big Bang:  matter density = radiation density era of recombination
    iii. before: opaque plasma

    E. The future of the expanding universe 

    1. relativistic cosmologies and the deceleration parameter ||| UPDATE NOTE!  the cosmologies described below assume that the cosmological constant is zero (the cosmological constant was included by Einstein to make his models static, but later assumed by most to be zero since observations showed the universe was expanding):  The most recent observations by two different groups using SN Ia data have shown that the universe is not only expanding, but actually ACCELERATING with time due to a NON-ZERO cosmological constant.  This data combined with the BOOMERANG, MAXIMA and WMAP data (see below) implies that the universe is flat with its overall density equal to the critical density.  However matter (including dark matter) makes up only about 27% of the critical density (normal baryonic matter = 4.4%, dark matter 23%), the rest (73%) comes from so called "dark energy" that is associated with the non-zero cosmological constant.  Some other characteristics of the universe derived from this data include:  the mysterious dark matter must be "cold" (ie:  made up of slow moving particles, this also leads to the conclusion that the neutrino mass must be less than 0.23 eV), The universe is 13.7 +/- 0.2 billion years old, the Hubble constant is 71 +/- 4 km/s/Mpc, the first stars formed only 100 to 400 million years aftter the big bang. |||
    a. open universe:  infinite in extent, unbounded, as time approaches infinity - rate of expansion of universe approaches constant velocity
    i. density less than the critical density
    ii. universe expands forever
    iii. 0 <= deceleration parameter < 1/2
    b. flat universe:  infinite in extent, unbounded, as time approaches infinity - rate of expansion of universe approaches zero
    i. density = critical
    ii. universe just barely expands forever
    iii. deceleration parameter = 1/2
    c. closed universe:  finite in extent, unbounded (like the surface of a sphere is unbounded), after finite time - universe begins to contract back to the "big crunch"
    i. density > critical
    ii. universe undergoes "big crunch"
    iii. deceleration parameter > 1/2
    2. relativistic cosmologies and the shape of the universe
    a. open universe:  negative curvature 
    i. hyperbolic
    ii. density < critical




















    b. flat universe:  zero curvature 
    given random inital conditions, this is the least likely case; however, see below for new evidence that the universe is indeed FLAT!
    i. flat
    ii. density = critical















    c. closed universe:  positive curvature 
    i. spherical
    ii. density > critical


















    3. measurements of the state of the universe
    a. deceleration parameter:  NOTE - recent SN Ia data indicates the universe is ACCELERATING with time, not decelerating!  This implies a non-zero cosmological constant (see E.1 above)
    b. density parameter
    i. number density with redshift
    ii. angular size with redshift
    iii. ave. size of angular variations in the Cosmic Microwave Background:   latest results from BOOMERANG, MAXIMA & WMAP  (best figure) projects indicate an almost flat universe as predicted by the inflationary big bang; density = critical density
    4. end state of the universe
    a. closed universe = Big Crunch
    b. open or flat universe = infinite expansion, black hole evaporations:  recent observations indicate this is the likely end state of the universe

    XI. The Early Universe

    A. Inflation

    1. flatness problem
    2. isotropy problem
    3. inflationary epoch

    B. Creation of matter and energy

    1. vacuum energy
    2. Heisenberg uncertainty principle
    3. pair production (virtual pairs) and annihilation

    C. After inflation, standard Big Bang

    1. thermal equilibrium and symmetry breaking
    2. neutrino-antineutrino background
    3. production of helium
    4. era of recombination
    a. density fluctuations in the early universe
    b. superclusters of galaxies
    i. hot dark matter
    ii. cold dark matter

    D. GUTs and TOEs

    1. four fundamental forces
    a. gravity
    b. electromagnetic
    c. strong nuclear
    d. weak nuclear
    2. GUTs unify EM, strong, & weak nuclear
    3. TOEs unify all, including gravity

    E. Super string theory - elementary "particles" are NOT point-like but rather string-like, existing in a 10 dimensional space-time with 6 dimensions "closed" on a subatomic scale:  current best bet for a correct GUT  (See the You Tube video "Large Hadron Collider Rap" for a take on how researchers at CERN are investigating GUT theories and the conditions just after the Big Bang!)

     

    XII.The Chances of Companionship (Epilogue)

    A. Life on Earth

    1. Characteristics:  Carbon based chemistry, single and multi-cell organisms with DNA in nuclei
    2. Origin:  Mechanism unknown, but seems to have developed as soon as Earth's environment was stable enough to support it

    B. Could life develop elsewhere?

    1. Since we currently have only one example of life arising in the universe, we do not know what the probability of the development of life may be:  it could be an extremely rare event, or it could be very common throughout the universe were similar conditions exist
    2. It does seem to be likely that the same (or at least very similar) conditions that existed on the young Earth, exist or have existed on many worlds in the galaxy, and we know that many of the organic chemicals that are the building blocks of life on Earth exist in abundance in interstellar space and other places in the universe

    C. Detecting "intelligent" life in the galaxy:  SETI - Search for Extra-Terrestrial Intelligence (a scientific method for detecting other "radio-communicating" civilizations)

    1. Defining "intelligent":  in order to have a measurable physical quantity that would unambiguously signal the presence of intelligent life and could be detected at extremely large distances, we must limit our definition of "intelligent" to those life forms that develop and maintain radio communications as part of their civilization - radio signals characteristic of intelligent communications could be detected by radio telescopes on the Earth even if they originate at very large distances from Earth
    2. Estimating the probability of detection - Drake's equation:  N = R* fp ne fl fi fc L
    a.  N = total number of "technological" civilizations currently existing in the galaxy
    b.  R*= number of Sun like stars formed per year in the galaxy (rate of Sun like star formation in the galaxy)
    c.  fp = fraction of Sun like stars with planets
    d.  ne = number of Earth like planets per Sun like star
    e.  fl = fraction of Earth like planets on which life arises
    f.  fi = fraction of  planets where life has arisen on which intelligent life evolves
    g.  fc = fraction of  planets where intelligent life has evolved that develop a "technical" = radio communicating civilization
    h.  L = effective life-time of a radio-communicating civilization
    3. Estimating the probability of detection - the terms of Drake's equation:  N = R* fp ne fl fi fc L
    a.  The main problem in using the Drake equation is that we have no way of estimating the values of most of the terms of the equation:  however the first two terms are related to observable astrophysical phenomena and can be reasonably estimated at least to within a factor of 10; R*= 1 to 10 Sun like stars/year, fp = quite likely close to 1 (100%) of Sun like stars have planetary systems (there are now at least five dozen Sun like stars with known planetary systems; present technology limits the detection to very massive planets, it is likely that with increased sensitivity and time smaller planets will be detected even for those stars where planetary systems have not yet been detected)
    b.  If we estimate fairly optimistic values for the next four terms we find that the last term in the equation (L = life-time of civ.) becomes the controlling term of the equation: let ne = 1 Earth like planet for every 10 Sun like stars (ne =  0.1) (note that this term may become less speculative as our detection limits for extra-solar planetary systems become more sensitive); now for the really speculative terms let us be completely optimistic and assign a value of one (100%) for all three fractions;  fl = fi = fc = 1 (i.e.:  all Earth like planets develop intelligent, radio communicating life forms); the Drake equation then becomes:  N = (1/year)(1)(0.1)(1)(1)(1)L = 0.1L  and the value of N becomes dependent mostly on the value of the life-time of the average radio-communicating civilization
    c.  The pessimistic estimation:  our civilization has only become sufficiently advanced to send or receive interstellar radio signals for only about the last 60 or so years and some would say our technical civilization has been lucky to last even that long;  let us take L = 50 years for our pessimistic estimation, which gives:  N = 5, if correct then the average distance between technical civilizations in our galaxy is 20,000 light-years which precludes any dialogue between extra-terrestrial civilizations (however, by sending out radio signals with information about themselves, a technical civilizations might at least ensure a continuing knowledge of their brief existence)
    d.  The optimistic estimation:  it is possible that when a civilization becomes sufficiently advanced to send or receive interstellar radio signals that is quickly becomes stable enough to exist for an extremely long period of time;  let us imagine that such a civilization could exist for a time equal to the present age of the disk component of our galaxy, approximately 10 billion years or L = 1010 which gives:  N = 1 billion, if correct then the average distance between technical civilizations in our galaxy is about 30 light years and we should be hearing from someone out there very soon... and you could be the person who detects the first contact!!!  See the SETI at Home website for details!

    D. Detecting "intelligent" life in the galaxy:  UFOs, evidence for extra-terrestrial civilizations?

    1.  Evidence that "unidentified flying objects" are extra-terrestrial spacecraft is almost exclusively anecdotal (someone reports an encounter or some other phenomena related to a UFO encounter with no physical evidence); this sort of evidence is almost never usable in a scientific investigation of any phenomena unless some sort of measurable quantities can be reliably and repeatedly extracted from the reports (which to my knowledge has never been the case for UFO reports); even imagery such as photographs or video are insufficient forms of evidence that at most allows others to experience the visual component of an encounter, but contain less potential information than the original encounter
    2.  While most scientists are optimistic that intelligent life exists somewhere else in the universe beyond ourselves, most would reject UFO as evidence of its existence.  See Phil Plait's Bad Astronomy web site for a short discussion of one chapter in his book Bad Astronomy which deals with UFOs and the reasons that most scientists (and amateur astronomers) reject the idea that UFOs are evidence for extra-terrestrial intelligence
    3.  The truth is out there.....?

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