Lecture Notes and Schedule

• Introduction to topics to be covered
• Challenge of vast range of scales, in space and time
• We are but one star of several hundred billion in our galaxy
• And there are billions of galaxies.....
• Nature of astronomy as a science
• Most fundamental assumptions: A. Copernican principle and B. Universality of laws of nature
• Scientific method: what it is all about
• Four fundamental forces: gravity, electromagnetic, strong and weak (nuclear) forces
• Light as waves (and particles), involving the electromagnetic force

Lecture 2: Fundamental forces and light as waves (Thur, Jan 16)

• Great puzzle of planetary movements: Earth or Sun centric?
• The Copernicus - Tycho - Galileo - Kepler great eras of change and discovery
• Kepler and elliptic planetary orbits in clearly a Sun-centric system
• Newton and gravitation to explain Kepler's orbits
• How to live and feel the speed of "light"
• Why SI units have some merit, vs the "English" system
• Significance of "quantum mechanics": energy of a photon related to its frequency
• Interaction of light and atoms, yielding spectral lines unique to each atom
• Electron energy levels for hydrogen, and the birth of "quantum mechanics"
• Emission and absorption of light, and resulting spectra

Lecture 3: Emission and absorption of light (Tues, Jan 21)

• Kirchoff's Laws about emission and absorption features
• Continuous spectrum emitted by hot solid or high-density gas
• Thin hot cloud can absorb photons of light passing through it, yielding a "dark-line" spectrum (absorption) unique to the elements in that cloud
• Thin hot cloud glowing by itself yields a "bright line" spectrum (emission), again unique to the elements in cloud
• Subtleties of the 'black body' or thermal radiation spectrum
• Doppler effect for both sound and light: shift the frequency/wavelength

Lecture 4: Telescopes and issues of observing (Thur, Jan 23)

• Doppler broadening by rotation of star
• Supermassive black hole discovered in center of M84 using Doppler shifts
• And just what is the wavelength/frequency of your cell phone?
• Principles common to our eyes, cameras, telescopes
• Examine range of big telescopes used in astronomy
• Effects of our atmosphere on light
• Light pollution, twinkling by turbulence, absorption by atmosphere
• Reflectors prevail over refractors for astronomy (discussion)
• Resolution and sensitivy of telescope improved by size of mirror (or lens)

Lecture 5: Telescopes in space and radio telescope arrays (Tues, Jan 28)

• Adaptive optics is able to remove many image distortions by atmospheric turbulence
• What light gets through our atmosphere, what does not
• Nature of instruments on telescopes for real analysis
• How and what do we observe from space
• Conserving angular momentum, useful to point space telescopes
• X-ray telescopes (grazing reflections)
• Radio telescopes (often arrays of dishes, and `aperture synthesis')
• Discussion of instrumentation in focal plane of different telescopes: imaging, spectroscopy, timing

Lecture 6: Fiske Planetarium #1: Elements of Sun as a star (Thur, Jan 30)

• Planetarium visit begins with brief lecture
• Overview of our nearest star, the Sun
• Regions of the Sun and their function: core, radiative zone, convective envelope, atmosphere
• Why is a star round? Equilibrium between pull of gravity and push of pressure
• Why does the Sun shine? Fusion reactions convert H to He, keep the center very hot
• Front page in NY Times: DKIST solar telescope first images and videos

Lecture 7: Powering the Sun by nuclear burning of hydrogen to helium (Tues, Feb 4)

• Overview of solar structure from inside out
• Solar granulation and surface convection: also source of solar sound waves
• Fusion reactions (p-p chain) convert H to He, center very hot
• Examine details of p-p fusion, including making neutrinos and gamma-ray photons
• Energy yield from H fusion is vastly greater than from chemical burning!
• Fusion burning of 1 kg of H into He (7 grams turned into energy) is equivalent to chemical burning of two units trains of coal (200,000 Tons)!

Lecture 8: Solar neutrinos, helioseismology, and rich solar magnetism (Thur, Feb 9)

• Puzzle of the solar neutrinos: how to capture these elusive particles, and thus test products of p-p chain
• Workings of the solar thermostat to maintain stable energy production in core
• How temperature and density varies with radius inside the Sun
• Examining solar granulation and sunspot structures in high-resolution detail
• How sampling of sound waves at the solar surface yields probes of the interior
• What helioseismology tells us about interior flows and structures
• Measuring magnetic field strengths in sunspots with Zeeman splitting of spectral lines
• Coronal mass ejections and flares from magnetic field reconnections

Lecture 9: Solar magnetism and its cycles, dynamo simulations, space weather (Tues, Feb 11)

• The solar magnetic cycle involving sunspots and variable activity
• Extensive EUV video sequences of coronal loops and flaring, and coronal mass ejections, as captured with both SOHO and SDO satellites
• Solar magnetic fields and their complex 11-year cycles
• Use of supercomputers to simulate dynamics (convection and magnetic dynamos) deep within the Sun
• Solar magnetism, solar wind, space weather and northern lights
• Effects of solar activity on our planet... and our technological society

Lecture 10: Stars: linking temperature and spectral classes (Thur, Feb 13)

• Observing stars other than the Sun: brightness, position, spectrum
• Devising a classification for stars based on absorption features in spectra (O,B,A,F,G,K,M) [Annie Cannon]
• Why surface temperature of star and spectral classification (O,B,A ..) are closely linked [Cecelia Payne-Gaposchkin]
• Turn to First Mid-Term Exam for the rest of class period

Lecture 11: Stellar types and the H-R diagram (Tues, Feb 18)

• Stellar luminosity and apparent brightness
• Distance from stellar parallax
• Revisit devising a classification for stars based on absorption features in spectra (O,B,A,F,G,K,M) [Annie Cannon]
• Cecelia Payne-Gaposhkin showed that Saha equation can explain spectral classification (O,B,A,F,G,K,M) in terms of surface temperature of star
• Saha equation predicts ionization states of different elements, with resulting spectral line strengths most sensitive to temperature
• Luminosity classes by width of spectral lines (I, II to V)
• Where different stars lie on H-R diagram in overview
• Measuring brightness of stars: apparent vs absolute magnitude (luminosity) requires knowing distance
• Determine radii of stars, if know luminosity and temperature

Lecture 12: Mass influences light output on main sequence (Thur, Feb 20)

• Brief overview of where different stars lie on H-R diagram
• Determine radii of stars, if know luminosity and temperature
• Four varieties of binary stars (based on detection)
• Estimating stellar masses from binary star data -- the only way to determine masses of stars other than by theory
• `Observed' mass-luminosity relation for main sequence stars
• C-N-O fusion cycle powers the more massive stars
• Nuclear fusion reactions increase very rapidly with temperature: thus massive stars really pour out the energy!
• Estimate how lifetimes on main sequence vary with stellar mass
• Outcome: massive stars have very short lifetimes on main sequence

Lecture 13: Star birth: Getting to the main sequence (Tues, Feb 25)

• Complete discussion of lifetime of stars on main sequence
• Cities of stars come in two varieties: open clusters (small) and globular clusters (big)
• Test ideas about evolution by looking at H-R diagrams of star clusters
• Peel-off from main sequence helps estimate age of cluster
• Overview of spiral galaxy: stars and gas in disk rotate faster than spiral pattern, with gas compressed as they enter these `traffic jams', leading to vigorous star birth in molecular clouds
• How large clouds of gas and dust (recycled from previous generations in spiral galaxy) may begin to collapse and form new stars
• Tyranny of too much angular momentum as star is being assembled
• Seeing into the `dusty cocoons' with near infrared wavelengths
• Nuclear furnaces slowly turn on and protostar approaches the main sequence

Lecture 14: Low-mass star after main sequence: red giants and supergiants, planetary nebulae, white dwarfs (Thur, Feb 27)

• Revisit stages in star birth, on the way to joining the main sequence
• Life after main sequence for low-mass stars -- becoming a red giant
• Red giant star, with H shell burning, has shrinking inert He core
• Degenerate matter has no thermostat, such as in red giant's core
• Helium flash in core (triple-alpha burning of He) removes degeneracy
• Burning He in core (horizontal branch)
• Discussion on `City of Stars' as sampling stellar evolution in a population
• Red supergiant phase (with double-shell burning of H and He)
• Planetary nebula involves shells `puffed off' from supergiant
• Remarkable shapes of planetary nebulae (PN): what may cause these?
• Why electron degeneracy pressure can only support a white dwarf up to 1.4 solar masses
• White dwarf of one solar mass is roughly Earth-size; more massive are smaller!

Lecture 15: High-mass star evolution to supernova end with neutron star (Tues, Mar 3)

• Revisit white dwarfs briefly
• Overview of massive star evolution
• Evolution of massive stars through giant and supergiant phases
• Fusion burning by He-capture of C, N, O .. in core and surrounding shells, like layers of onion: iron is the end of line!
• Strong winds from massive stars, even big ejecta (Eta Carinae)
• Sudden brightening of massive red giants/supergiants can yield "light echos"
• With enough core mass of iron, electron degeneracy can no longer support the star: `core collapse' supernova explosion
• Supernovae (SN) can create neutron stars, formed from their collapsed iron cores
• SN explosion leads to nucleosynthesis, making most elements in universe heavier than iron
• Remnant left behind could be a neutron star, supported by neutron degeneracy pressure, or black hole
• Pulsars: rapidly rotating neutron stars with fierce magnetic fields
• Listen to radio emission from several pulsars (some go with heavy metal beat, others like bongo drums, some are a fast buzz!)

Lecture 16: Fiske Planetarium #2: Massive stars, supernovae and black holes (Thur, Mar 5)

• Brief revisit of massive star evolution, ending in core-collapse supernova
• Discovery of radio pulses from unknown source, with very steady beat!
• Detailed look at pulsars: rapidly rotating neutron stars with fierce magnetic fields
• Synchrotron radiation is source of intense light beamed by pulsars
• Pulsars: `lighthouses in the sky' gradually slow down, using rotational energy to power the beams
• Fly through our galaxy, with stopping at many places, using full Fiske Sky
• "Black Holes: The Other Side of Infinity" (23 minute DMSN and Nova program, with CU faculty involved in original production)

Lecture 17: Supernovae, mass transfer in binaries and awakened white dwarfs (Tues, Mar 10)

• Revisit synchrotron radiation providing the beams from pulsars
• Demo of one variant of neutron star (the `bowling ball').
• Crab nebula supernova (4 July 1054) and pulsar show stunning behavior in Chandra and Hubble movies
• Mass exchange by Roche lobe overflow in binary system: Algol paradox
• How mass transfer onto a neutron star in a binary system can spin it up
• Binary mass transfer onto white dwarfs can yield recurrent novae, or even detonate entire star (fusion of carbon) in supernova explosion
• Such `white dwarf supernovae' are superb bright reference `candles'
• Observational differences between massive-star `core-collapse supernovae' (Type II) and white-dwarf supernovae (Type I)
• With white-dwarf SN, nothing left behind, as seen with Brahe and Kepler supernovae shells
• Hot accretion disks always formed around objects on receiving end of binary mass transfer
• Similar mass transfer onto neutron stars, with helium flash burning, may explain x-ray bursters

Lecture 18: Visiting a most famous supernova in modern times: SN 1987A (Thur, Mar 12)

• Revisit white-dwarf supernovae, and how they become "standard candles"
• Supernova 1987A as an explosion of a star in the nearby Large Magellanic Cloud observed ~160,000 years later by us on 24 Feb 1987 with modern equipment and satellites
• Star was a bright blue supergiant, so core-collapse supernova, with likely neutron star or black hole (but currently obscured)
• Brief burst of neutrinos detected from this SN for the first time
• Evolving structure, shocks and emission from SN 1987A -- seeing changes in `real time', as also predicted by Dick McCray here at CU
• As blast wave arrives at previous ejecta, systematic heating and brightening of seemingly ring-shaped structure
• Examined other famous SN remnants in Milky Way, from the time of Flamsteed in ~1680 (Cassiopeia A, with neutron star at center), Kepler in 1604 (probably white-dwarf SN), and Tycho Brahe in 1572

Lecture 19: Einsteins's spacetime: black hole singularities and detecting them (Tues, Mar 17)

• Einstein argued space and time are not distinct if speed of light is constant for all observers: thus need 4-dimensional `spacetime'
• Time slowed down by moving fast or experiencing strong gravity
• Strong gravity can seemingly bend light and redshift its frequency: warping of space and time by gravity
• Escape cones for light close at the `event horizon' around black holes, at a `Schwarzschild radius'
• Just three numbers describe a black hole: mass, electric charge, angular momentum
• Ergosphere: a spinning black hole drags nearby spacetime along
• Overview of Milky Way: spiral galaxy with thin disk, bulge and halo
• Since stars and gas are always moving, inspires the galaxy song `The Galaxy / Lighten Up'

Lecture 20: Our Milky Way Galaxy: Its overall structure and motions (Thur, Mar 19)

• What happens from view of mothership or probe when approaching a black hole
• Return to black holes topic: How to detect a black hole
• Cygnus X-1 first candidate for revealing a black hole in binary system
• The very strange object SS433, likely binary mass flow onto black hole that sends out precessing relativistic beams
• Motion of stars in our galaxy: disk stars in nearly circular motion, halo and bulge stars in swooping orbits that dive through disk
• Elements involved in building a spiral galaxy like our own Milky Way
• Explaining rotation curve with radius in disk calls for much more matter than is visible: thus `dark matter'
• Our galaxy, like most, embedded in a much large spherical halo of dark matter
• Inventory of galaxy disk: stars (~90% by mass), gas (~10%), dust (1%)
• A little dust goes a long way in absorbing/obscuring light
• Interstellar medium (ISM), or stuff between the stars: its various components visited

Lecture 21: Spiral structure and the interstellar medium (ISM) (Tues, Mar 31)

• Revisit "inventory" of interstellar medium (ISM) states: cold, warm, hot, really hot!
• Superbubbles blown by multiple supernovae, can even burst out of galactic disk
• Remarkably different views of ISM at distinct wavelength ranges
• First look at spiral patterns outlined by bright O & B star associations
• Resulting beautiful structures in star birth regions with O and B stars carving out holes
• Examine how spiral patterns are made in the disks of galaxies, including our own: gas and stellar traffic jams
• Spiral patterns outlined by bright O & B star associations, with vigorous star birth occurring in spiral arms through compression of molecular clouds
• What a micron-sized dust particle looks like, and how it absorbs and reddens visible light
• Longer wavelenghts of infrared and radio waves can see through the dust

Lecture 22: Mapping of Milky Way structure and discovery of other "island universes" (Thur, Apr 2)

• Role of dust in absorbing/scattering light, with mischief in confusing distance estimates
• Radio observation in 21-cm line of atomic hydrogen (HI) provide mapping of spiral structure in disk of our Milky Way
• Radio astronomy of 21-cm emission from spin up/spin down transition in HI paved the way for MRI imaging in medicine
• How we map spiral structure in our galaxy, with Doppler shift of 21-cm line crucial ingredient
• Detailed observational evidence for supermassive black hole (SagA*) at center of Milky Way
• A great step forward in 1924 with new 100-inch Hooker telescope on Mt Wilson above Pasadena and LA
• Edwin Hubble is able to distinguish Cepheid variables in Andromeda, shows that it lies way outside of Milky Way -- thus there are other island universes, now called galaxies!
• Classifying galaxies by appearance and shape: spirals, barred spirals, ellipticals, irregulars (Hubble's `tuning fork')
• Great surprises from Spitzer space telescope imaging Andromeda in infra-red

Lecture 23: Rich world of galaxies and measuring cosmic distances (Tues, Apr 7)

• What sample galaxies (spirals, barred spirals, ellipticals) look like, and where found
• Big picture of universe: network of galaxy clusters and superclusters, with about 100 billion galaxies in all
• Our local group of galaxies: Andromeda, Triangulum and Milky Way are the heavyweights, then LMC and SMC, plus small ones, about 21+ in all
• Hubble busily measures redshifts of many galaxies, announcing in 1929 that redshifts of galaxies appear to increase with distance from us
• Hubble's Law and what it means: we are in an expanding universe!
• Measuring cosmic distances is a big challenge: identify `standard candles'
• Parallax, main-sequence fitting, Cepheid variables, Tully-Fisher relation and white dwarf each provide ways to estimate increasingly greater distances
• Distance ladder using overlapping standard candles

Lecture 24: Expanding universe, quasars as active galaxies, galaxy collisions (Thur, Apr 9)

• Knowing the redshift of an object, can use Hubble's Law itself, once calibrated, for estimating biggest distances (or `lookback time')
• Most mapping of 3-D structure of galaxy clusters and superclusters thus accomplished using Hubble's Law
• Quasars - how discovered at large redshifts through bright emission lines of hydrogen
• Model of `active galaxies', including quasars: accretion disk around supermassive black hole, particle beams on axis of spinning disk form jets
• Synchrotron emission from jets can explain beams, seen also as great `radio tails'
• Examine radio galaxies for their synchrotron emission from jets and tails
• Visit elliptical galaxy Centaurus A with jet and central supermassive black hole (SBH); has big dust lane and is radio source with big lobes
• Remarkable scaling of SBH in many galaxies with their halo masses
• Collisions or `interactions' between galaxies must be common
• Simulations of colliding galaxies yield bridges and tails, many of which are observed
• Modelling the `Mice' and the `Antennae' as interacting galaxies

Lecture 25: Galaxy evolution and active galactic nuclei (Tues, Apr 14)

• Modelling the possible future crash of Andromeda with our Milky Way
• Many messages from galaxy interactions (collisions):
• 1. Must be common early in dense clusters
• 2. Spiral galaxies can tumble together to form elliptical galaxy
• 3. Vastly increased star birth (starburst)
• 4. Rapid feeding of massive black hole (quasars and radio galaxies);
• 5. Rapid variability of quasars says that emission region is very small
• Revisit "active galactic nuclei" (AGN), for the beautiful emission tails or jets revealed by radio telescopes.
• Examine very high resolution images by HST of accretion disks around the central supermassive black holes in elliptical galaxies hosting an AGN

Lecture 26: Gravitational lensing and dark matter (Thur, Apr 16)

• Case for dark matter as huge surrounding halo to spiral galaxy: Flat rotation curves
• Galaxy clusters reveal presence of dark matter in three ways:
• 1. Large random velocities of member galaxies,
• 2. Hot x-ray emitting gas in cluster,
• 3. Gravitational lensing by galaxy clusters
• Many examples now of gravitational lensing by clusters
• Just what might be dark matter? MACHOs and WIMPS may offer possibilities
• Cosmological models of universe, first look

Lecture 27: Third Mid-Term Exam (on Canvas/Quizzes) occupies the full class interval. Tues, Apr 21)

Lecture 28: Cosmology and general relativity predictions or options (Thur, Apr 23)

• Cosmological models of universe
• Brief history of how Einstein's General Relativity Theory (GRT) was quickly used by Friedman and Lemaitre
• Dark matter and fates of universe
• Three choices for fate of universe: coasting (open), critical (flat), recollapsing (closed)
• Cosmic microwave background (CMB) and its many implications
• Subtle aspects of the very small variations in CMB

Lecture 29: First three minutes and later eras in universe (Tues, Apr 28)

• Implications of high-resolution mapping of CMB
• Dark energy approximately ~68%, cold dark matter ~27%, ordinary (baryonic) matter ~5%
• Remarkable that stars make up only about 10% of ordinary matter: the vast majority must be intergalactic gas, especially amidst the giant clusters of galaxies, as seen in strong x-ray emission
• This is an accelerating flat universe with dark energy as key ingredient
• Gamow led the way with calculating nucleosynthesis within the big bang and which elements would be produced - looking at first 3 minutes in the `fires of creation'
• Discuss rapid eras of particles, nucleosynthesis, and nuclei
• Recombination: after 380,000 years, universe cooled to about 3000K, atoms can form and photons can begin to travel freely -- now viewed as CMB

Lecture 30: Building the large-scale structure and galaxies in our universe (Thur, Apr 30)

• Era of galaxies and stars started after about 1 billion years
• Simulations reveal large-scale structure formation in universe, leading to voids and sheets and galaxy clusters
• These major cosmological simulations (Millenium, Illustris, ...) reveal crucial role of cold dark matter in resulting structure
• Ordinary barionic matter and photons by being too mobile (or hot) would not build such large-scale structures themselves, but barionic matter would be pulled into the gravitational wells in due course
• Discuss the great outstanding questions about cosmology and our universe
• Revisit our Andromeda galaxy (M31) for a celebration of what high-resolution IR imagery from space can reveal