Download WEDNESDAY JULY 1

WEDNESDAY JULY 1
TIPS FOR SUCCESS
 Pay attention to the objectives of each lecture
 Math problems
 Write down what you’re given, what you want, and anything else you
know that is not stated explicitly
 Write down any/all formulas you may need
 Formulate a plan to get from what you have to what you want
 Calculations themselves don’t get you many points, setup does
 Answer all the parts of each question
 Come back to difficult questions later and don’t freak out
THE SUN
 Core: fusion
Radiative zone: energy transferred by photon collisions
Convective zone: energy transferred by bulk motion
Photosphere: “surface” of Sun that we see, magnetism
Chromosphere: lower atmosphere with activity
Corona: extends throughout Solar System
 Discuss: In what ways does the Sun interact with Earth?
 Think-Pair-Share: Sunspots appear dark because…
 A- they are not giving off light
 B- light is being absorbed in an outer layer of the Sun
 C- they are cooler than the surrounding regions
 D- the Sun’s light is being absorbed by magnetic fields
 E- an object is passing in front of the Sun
STELLAR PROPERTIES
 Wien’s law: relates wavelength (color) to
temperature
 maxT = 2.9 x 10-3 mK
 Stefan-Boltzmann law: relates temp, size,
and luminosity
 L = AT4 = 4R2T4
 High-mass stars use their fuel at a faster
rate than low-mass stars so they live a
shorter amount of time
 Think-Pair-Share: Star A is 3 times as hot
as Star B but Star B is 15 times as luminous.
Which is bigger?
FUSION
 Stars shine because (nuclear
binding) energy is released
during fusion
 Up to a certain point, which
is ________________
 Nuclear fusion requires
both high pressures and
densities
 Discuss: How does fusion
sustain a star? Consider
self-regulation of fusion.
STELLAR EVOLUTION
 Low-mass stars become white
dwarfs within a planetary nebula
 Under special conditions they can
become Type Ia Sne
 High-mass stars can become neutron
stars or black holes
 Each new phase of stellar evolution
involves collapse
 Discuss: A supernova explosion
within 100 ly of Earth could be
catastrophic for us. How would you
go about determining if you were in
any danger from it?
GALAXIES
 Spirals: disk, halo, bulge
 Star-forming regions, “young”
 Elliptical: spheroidal
 Old “red and dead”
 Milky Way: large spiral
 Nebulae, satellites, Sgr A*, stars, ISM,
globular clusters
 Dust causes reddening that is separate
from redshift
 Think-Pair-Share(s): In the Venn
diagram shown to the right, what is the
position of each of the following
characteristics?
 Star formation, lots of gas/dust, no
gas/dust, mostly cool stars, groups of
hot bright stars
AGN
 Quasars: quasi-stellar radio sources
 Remnants of the early Universe
 Important for cosmology because they
provide evidence of a young Universe
and can help us determine conditions in
the beginning
 Powered by accretion of mass from a
disk onto a supermassive black hole
 Broad and narrow lines, radio jets, dusty
torus, accretion disk, SMBH
DARK MATTER
 Dark matter makes up 80% of all the
matter in the Universe
 The interesting stuff is non-baryonic (not
protons and neutrons and stuff that we
know/understand)
 No lab detections yet
 Main astronomical evidence
 Flat rotation curves of spiral galaxies
 Gravitational lensing
 Bullet Cluster collision
 Main candidates: MACHOs and WIMPs
EXPANSION
 Hubble’s law gives the relationship between
how fast a galaxy is receding from us and its
distance
 v = H0d
z = v/c = /
 Space itself is expanding
 Hubble’s law only applies over very large
distances
 But not too large cuz then dark energy
 Nearby galaxies under influence of gravity
 Hubble’s constant does not change
throughout space but does over time
 Type 1a supernovae are great standard candles
BIG BANG
 6 main stages
 Big Bang: start
 Separation of 4 forces: gravity, strong nuclear,
weak nuclear, electromagnetic
 Inflation: rapid growth
 Annihilation: matter-antimatter asymmetry
 Nucleosynthesis: forming of protons, neutrons,
and nuclei
 Recombination: electrons paired with nuclei and
photons escaped
 Discuss any problems with the Big Bang theory
(not the TV show) that you can think of.
EVIDENCE
 Observational evidence killed the steady-state theory
 Cosmic Microwave Background was detected in every direction
 Mostly smooth, some fluctuations  What are these fluctuations?
 Created during era of recombination
 Discuss the significance of the tiny variations or “ripples” in the cosmic
microwave background.
 Why is the CMB at ~3K when recombination occurred at ~3000K ?
 Other evidence: Hubble’s law, Olbers’s paradox, abundance of elements
WRAP-UP
 Don’t sweat the math but also don’t skip it entirely
 Really don’t skip anything

No make-up this time so just write stuff
 Use the process laid out in this lecture!
 Study lecture objectives
 Mostly conceptual
 Good luck!
 Write your paper – due Thursday