Download Review Sheet and Study Hints - Tufts Institute of Cosmology

Material Overview and Study Aid
History & Gravity
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Earth: the shape of the earth: flat versus round;
 longest/shortest days of the year: how to determine them;
 day and night: what causes them: sun rotating around earth, or earth rotating around its own
axis;
 how to determine the size of the earth
 size and distance of the sun & the moon & stars
Geocentric and heliocentric system - main difference; how do we know which is correct?
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Gravity: Explanations by Aristotle, Newton & Einstein – differences between them
Principle of Equivalence
What is the nature of Gravity? What is a force in the General Theory of Relativity?
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What is scientific methodology? What are natural Laws?
Newton’s thought experiments and the discovery of the universal law of gravity
Important Concepts
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Luminosity & Flux – Difference – Inverse square law
Parallax & Parsec; Light year -- difference
Magnitudes – define them
Distance Modulus
Energy & Light
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Nature of light:
 Give examples of what items emit light.
 How does each experiment prove either the Wave or the Particle nature?
 What is a photon? What is a quantum?
 What is the relationship between wavelength and frequency? (c=)
 How do you calculate the energy of a photon? (E=h)
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Electromagnetic Spectrum:
 Draw a schematic diagram of the Electromagnetic Spectrum and label major regions in order of
wavelength or frequency (e.g. IR, Visible, etc).
 What distinguishes these regions? What do they all have in common?
 Be able to show the direction of increasing wavelength, frequency, and energy.
 Can you hear radio waves?
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Black body radiation:
 Define black body radiation?
 What kinds of objects produce black body spectra?
 Draw a black body curve. Label the axis. Given several blackbody curves, be able to tell which one is
hotter, which one is redder, and which gives more energy per unit area.
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What is Wien's Law (know max is proportional to 1/T)?
What is the Stefan-Boltzman Law (know Flux is proportional to T4)?
Why are some stars red and others blue? What does that tell us about the stars?
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Types of Spectra (and “Kirchhoff’s Law’s”):
 What is the difference between emission, absorption, and continuous spectra?
 What types of objects produce emission line spectra?
 Under which conditions do you get an absorption line spectrum?.
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Spectral Classification:
 What are the spectral classes? What is the property which distinguishes them.
 Know the approximate temperature for A stars, G stars, and M stars.
 What spectral features distinguish the various spectral classes?
 Why do A stars have very strong Balmer lines and both B and K stars have weaker lines?
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Stellar Properties – be able to define them
 Herzsprung Russel Diagram – be able to draw it
 What are: Brightness, Luminosity, Energy of a Photon, Energy of a Star, Flux, Apparent and
Absolute magnitude; define these quantities.
 Be able to compare brightness, magnitude, luminosity, flux, intensity
 Luminosity, temperature, color and radii of different stars; --- be able to do basic calculations
involving ratios
 For which properties do you have to know the distance?
 The Interstellar Medium (ISM)
 List various types of Interstellar Clouds
 Comment on gas/dust densities and temperatures
 Comment on colors, and in particular explain the astrophysical processes that give rise to
the different colors (these include scattering of light and reflection; the process of reddening
due to “de-blueing”; the Bohr model, how that explains the emission from hot gas, and how
this explains why hot gas shimmers with a reddish tint)
 Parallel questions
 Why is the sky blue?
 Why is the sun red at sun set?
 Be able to distinguish between emitted and reflected light.
 Star Formation
 Under which conditions can stars form?
 comment on masses, densities and temperatures of ISM
 triggering mechanisms? what makes stars form?
 how does this depend on the mass?
 What do star formation regions look like?
 be able to comment on pictures!!!
 when and under which conditions can you see the “forming” stars?
 how does starlight affect the properties of the ISM?
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 Proto-Stellar Evolution
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What is the Energy Source?
The formation of Accretion disks & Formation of Planets
Why are jets formed?
Observations at Infra Red Wavelengths of Protostars
The Evolution in the HRD
Hydrostatic Equilibrium
 The Evolution in the Herzsprung Russel Diagram (HRD)
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Draw and label it
 Include magnitude (M), luminosity (L/Lo), color or color index (B-V), spectral type
OBAFGKM and temperature.
 Point towards increasing luminosity, temperature, radius, redder color.
 Point arrows towards increasing main-sequence-radius and m.-s.-mass.
Evolutionary Tracks
 draw the position of main sequence stars, white dwarfs, giants and supergiants,
horizontal branch stars, variable stars, protostars
 draw evolutionary tracks in the HRD for stars of different masses
 comment on relative evolutionary time-scales
globular cluster HRD’s
 main sequence turnoff and ages
 distance determinations
use the HRD to determine star-formation histories in galaxies
 The Evolution of Stars
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how do we study the evolution of stars?
how, in what order, and under which conditions, do stars evolve into red giants, super
giants, horizontal branch stars, cepheid variables, asymptotic giant branch stars, white
dwarfs, neutron stars and black holes?
how does the star’s mass affect its evolution?
 what are the basic differences in evolution between low and high mass stars?
what happens in the cores of stars?
what do we observe on the surface?
 how do luminosity, radius and surface temperature change?
Concepts: hydrostatic and thermal equilibrium
 The Death of Stars
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what are stellar end-states?
 which factors determine the ultimate fate of stars?
 general properties of
 white dwarfs;
 neutron stars and pulsars
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 black holes
 comment on chemical composition, masses, densities, sizes
mass loss, stellar outbursts and remnants
 supernova, nova, and planetary nebula
 what do these look like? comment on pictures
 under which conditions do you get what?
 exactly why and how do they happen?
 The Formation of Elements
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Light elements
 H He and He C
 why do only low mass stars have a He-flash
 why is electron degeneracy important? (what is electron degeneracy?)
heavier elements
 onion shell analogy
 under which conditions do you form heavier elements?
 why will the sun never form elements heavier than oxygen?
 why can you only produce elements up to iron inside stars?
 how do you form elements heavier than iron?
 The Milky Way
 The Size and Shape of the Milky Way
 How to go from the Milky Way in the sky to an image of our Galaxy
 Counting stars, determining distances; Kaptyn’s Universe;
 Shapley-Curits Debate --the size and shape of the universe
 Resolution of debate – both scientists were right and wrong
 Observing the Milky way at different wavelengths
 What constituents of the Galaxy do you see in the Visual, IR, radio, Xray
 What is 21 cm emission ?
 How do you observe molecular clouds ? Dust ? Gas ?
 How do you study the spiral arm structure of the Milky Way ?
 What produces the Spiral Arms
 The Winding dilemma
 Spiral Desnity waves
 Galaxies
 Classification
 What are the major differences in shape between spiral and elliptical galaxies?
 What are the major differences in other properties of spiral and elliptical galaxies?
 What is the tuning fork diagram?
 Explain how color, stellar populations and gas and dust vary along the Hubble sequence.
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Is the Hubble sequence a good classification?
 Stellar Evolution in Galaxies
 How do you identify young/old star clusters?
 Overall color and luminosity evolution
 Globular cluster diagrams and ages
 Role of Gas and Dust in a galaxy – interplay with stars
 Stellar Populations
 How to study the stellar populations – how to model them
 What information do you get from spectra of galaxies
 How do stellar spectra relate to galaxy spectra
 Why do interacting/peculiar galaxies show such a wide spread of colors
 What are starburst galaxies
 Evolution and Formation
 Describe a theory about the formation of spirals.
 What evidence do we have for that?
 In what sense is the formation of ellipticals different from that of spirals?
 In what sense was Hubble correct/incorrect with this evolutionary proposal?
 How do galaxies in the past look different from galaxies today?
 Be able to look at pictures of field galaxies and clusters and comment
 Be able to look at the Hubble deep fields and comment
 What information have we obtained from the Hubble Deep fields about galaxy
evolution?
 Environments of Galaxies
 Where do you find mostly Spiral galaxies? Elliptical?
 What does that tell you about galaxy evolution?
 Mechanisms to transform spirals to ellipticals – be able to list and explain them
 Galaxies with Black Holes
 How do you identify an active galaxy ?
 How is an active galaxy different from a normal galaxy ?
 Comment on differences in appearance
 Comment in differences in radiation mechansims
 Comment on differences in spectra
 What makes an active galaxy active ?
 Waht types of active galaxies exist ?
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Evidence for black holes in galaxies?
Do all galaxies have back holes in their centers – why/ why not ?
Is there evidence (what evidence ?) in our own galaxy about a black Hole ?
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Radio-galaxies – lobes & Jets
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Schematic diagrams
Structure differences in radio lobes
Optical jets – radio jets differences/similarities
Do superluminal jets exist ?
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How were active galaxies discovered ?
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Unification models
 Why were they proposed
 What is the general idea behind them
 Draw schematic diagrams
 Be able to explain those schematic diagrams
Cosmology Topics in Astronomy
 General questions:
 How do we know the universe is evolving? Exactly what is evolving?
 What did the Universe look like in the past? How do we know that? Extrapolate into the
future - what will the universe look like in the future?
 Redshift.
 Explain the concept.
 How do we measure redshifts and velocities?
 What is the difference between redshift and reddening? Difference between Doppler
shift, cosmological redshift and gravitational redshift?
 Expansion of the Universe
 Hubble’s law
 determining the age of the Universe.
 Why is the accuracy of Ho so important? How do we measure Ho?
 Why does the expansion of the universe slow down?
 The Big Bang Theory
 Evidence for the Big Bang?
 Is there a possibility of a Big Crunch? Under which conditions? What evidence do we
have that this may happen?
 Problems with the Big Bang Theory?
 4D-Space-Time.
 Why do we need it? Visualization aids of the expanding universe.
 Is the universe finite or infinite (in what sense is it finite or infinite)? Does it have and
edge, or a center?
 What does it expand into (why is this a wrong question)?
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 Universe Models
 What are the possible fates of the universe? Be able to comment on the open, closed and
critical universe (draw how the scale of the universe changes with time).
 What is the geometry of space-time in those models? How can we visualize that?
 How will we be able to differentiate between these models?
 The cosmological constant, Einstein’s blunder, and why it may nevertheless be
important.
 The Metric
 What is it – how can it be derived
 What does the general form of the Robsertson-Walker Metric tell us?
 How and when do we use the metric?
 Be able to explain in what sense the metric is able to describe the Structure of Space
Time
 General Relativity
 Difference between GTR and Newtonian Gravity
 Principle of Equivalence
 Proof of GTR
 Understand Einstein’s “Link” between Structure of Space time and Kinematics
 The Cosmological Principle
 What does it state?
 What’s the meaning of Homogeneous and Isotropic
 Is the Universe truly homogeneous and Isotropic?
 Tests for homogeneity
 Age and Fate of the Universe
 Be able to calculate the age of the mass-less Universe
 How does this age differ for an open critical and closed universe
 B able to calculate the age of the critical Universe
 The need for an accelerating universe
 Ho, qo and 
 Definitions of all of them
 Be able to summarize efforts and challenges in determining Ho
 Be able to summarize (at least two) tests of determining qo
 Be able to explain how to “measure” 
 The Cosmic Microwave Background
 What type of radiation is this
 How was this radiation discovered
 From what epoch of the early universe is it? (Be able to calculate z of recombination)
 What are the general conditions of the universe when this radiation was emitted?
 What cannot we see beyond the CMB?
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Why is it Black Body Radiation?
In what sense is this radiation “evidence” for the Big Bang?
What do COBE and WMAP data tell us?
 Problems with the Big Bang Model
 Flatness Problem
 Horizon Problem
 Matter-Anti matter Problem and Symmetry Breaking
 How the Inflationary Universe solves these problems
 The first 3 minutes
 What is the Planck Time?
 What is the Heisenberg Uncertainty Principle and what is its significance in the Early
Universe?
 What is the significance of the Planck Mass & Planck Length?
 What is the condition for creating a new (non-virtual) particle?
 What is Baryo-synthesis?
 What is Neutrino decoupling and why could this be an important epoch?
 When was the inflationary epoch and what is it?
 What & when is the era of recombination?
 What & when is the era of decoupling?
 Forces of Nature
 What are the four forces of Nature?
 What are the carriers of each of the four forces?
 What are Grand Unified theories and when are they important?
 What do we mean by Symmetry breaking?
 Nucleosynthesis
 Making Hydrogen – when & how?
 How to make Helium in the Big Bang
 Why & how do we get 25% of Helium
 Where do all the remaining elements from?
 Dark Matter
 Example of Baryonic dark matter
 Examples of Hot dark Matter
 Examples of cold dark matter
 Possible distributions of Dark Matter – why this is relevant to galaxy formation
 Galaxy Formation and Evolution
 Formation scenarios for galaxies like the Milky Way
 Formation scenarios for Elliptical galaxies
 Nature versus Nurture debate – do ellipticals form through merging?
 Evidence from the HDF and UHDF – what does that tell us about galaxy formation and
the subsequent evolution of galaxies?
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