Learning Objectives: Chapter 13, Part 1: Lower Main Sequence Stars. AST 2010: Chapter 13. AST 2010 Descriptive Astronomy

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1 Chapter 13, Part 1: Lower Main Sequence Stars Define red dwarf, and describe the internal dynamics and later evolution of these low-mass stars. Appreciate the time scale of late-stage stellar evolution (accelerated aging) and explain it qualitatively. Describe the structure and internal dynamics of a low-mass star in the yellow giant phase. Identify the event that leads to the red supergiant evolution stage. Describe the ejection of a red supergiant s outer layers and explain the mechanism that causes it. Define planetary nebula and explain why these nebulae glow, i.e. emit light. Appreciate the time scale over which a planetary nebula exists. Describe the physical properties of white dwarfs and appreciate their nature as a stellar remnant. Based on the above predict, from stellar evolution models, the eventual fate of our Solar System. AST 2010: Chapter 13 1

2 Chapter 13, Part 2: The Evolution of Binary Stars Describe the mechanism of mass transfer in binary star systems. Explain the existence of binary systems consisting of a high-mass main sequence star and a low-mass giant. Define accretion disk and describe its role in mass transfer from a giant star to a white dwarf companion. Define nova and describe the physical mechanism that causes a nova explosion. Can a nova recur? Define what is meant by the Chandrasekhar limit, and explain why white dwarfs > 1.4 M sun are not found. Define Type 1a supernova and describe the physical process resulting in such a supernova explosion. Describe the observable remnant of a Type 1a supernova. Identify the maximum distance to which Type 1a can be used as standard candles. AST 2010: Chapter 13 2

3 Chapter 13, Part 3: The Deaths of Massive Stars Define nucleosynthesis and explain how and why it happens inside stars. Describe the process by which massive stars fuse successively heavier and heavier nuclei in their cores, and explain why each fuel type is exhausted more quickly than the previous. Explain why iron fusion cannot provide energy to support a star s weight. Appreciate the composition of the expanding gas cloud from the explosion, its role in seeding the ISM with heavier elements, and the role of the blast wave in triggering molecular cloud collapse. Discuss the light curves of Type II supernovae and explain why they are NOT useful as standard candles. Discuss the case of SN 1987a and explain its importance as supporting evidence for astrophysical models of Type II supernovae. Discuss a few examples of Type II supernova remnants. How do they differ from those of Type Ia supernovae? AST 2010: Chapter 13 3

4 Chapter 14, Part 1: Neutron Stars Define neutron star, and characterize its origin as a remnant of core-collapse supernova. Define pulsar and discuss their discovery and eventual explanation. Explain the mechanism by which regular pulses are produced by neutron stars. Define synchrotron radiation and its relation to neutron stars. Discuss the lighthouse model and how it explains the regularity of pulsar emissions. Define pulsar glitches and discuss their commonly accepted explanation.. Describe how the spin of neutron stars changes over time, and how this change leads to glitches. Discuss the theorized effects of gas pulled from a companion onto a neutron star. Define and distinguish x-ray pulsars and magnetars. AST 2010: Chapter 14 4

5 Chapter 14, Part 2: Black Holes Define black hole and describe how a core-collapse supernova remnant might become one. Define and distinguish Schwartzschild radius and event horizon. Discuss the predictions of GR that have been confirmed: deflection of starlight, precession of Mercury s orbit, gravitational red shift of light from white dwarf; success of GPS technology. Explain how to detect a black hole and give examples of objects that have met the criteria. Define gravitational waves and describe how astronomers are trying to detect them. Explain why Taylor and Hulse got the Nobel prize. AST 2010: Chapter 14 5

6 Chapter 14, Part 3: Compact Objects with Disks and Jets Define accretion disk, and explain why they are often found in binary systems of compact stellar remnants. Describe what a gamma ray burst is. Discuss the proposed explanations for each type of GRB: hypernovae for long-duration bursts, magnetar starquakes and kilonovae for the short-duration variety. Appreciate the luminosity of GRBs and discuss the possible effects on Earth of a GRB occurring inside our galaxy. AST 2010: Chapter 14 6

7 Chapter 15, Part 1: Discovery of the Galaxy Identify the shape of the Milky Way Galaxy, and discuss some simple observations that support this idea. Discuss the Herschels model of the Galaxy, the methods they used to arrive at it and the problems with those methods. Characterize Shapley s model of the Galaxy and explain how he determined the location of its center. What is notable about this model? Discuss the sources of error in Shapley s calculations. Give the modern value for the size of the Galaxy and compare with those of the Herschels, Kapteyn, and Shapley. AST 2010: Chapter 15 7

8 Chapter 15, Part 2: Structure of the Galaxy Define the elements of the Galaxy s structure: disk, central bulge, halo. Locate the globular clusters within the volume of the Galaxy. Describe and contrast the motion of disk stars from that of halo stars. Define differential rotation as it applies to the Galaxy. Define rotation curve and explain how the distribution of mass in the Galaxy is measured. Explain why the Galaxy s measured rotation curve differs from what is expected based on the distribution of visible matter, and know the currently accepted explanation for this result. AST 2010: Chapter 15 8

9 Chapter 15, Part 3: Spiral Arms and Star Formation Identify the clues from other galaxies that suggest that our own galaxy may have spiral arms. Define spiral tracer and identify the spiral tracers that are used to map out the spiral arms in our Galaxy. Explain why only short-lived objects are chosen as spiral tracers. AST 2010: Chapter 15 9

10 Chapter 15, Part 4: The Nucleus of the Galaxy Explain why the center of the Milky Way is invisible to us in optical wavelengths. Describe the evidence that points to a very massive and powerful object at the very center. Be aware that this object is called Sgr A*. Explain how the mass of Sgr A* is measured and characterize the result. Be aware of the currently favored hypothesis about the nature of Sgr A*. AST 2010: Chapter 15 10

11 Chapter 15, Part 5: Origin and History of the Milky Way Identify the various elements formed within stars: helium, carbon & oxygen, iron; with the types of stars that can produce them via nucleosynthesis. Define and distinguish Population I from Population II stars, and locate them within the structure of the galaxy. Define galactic cannibalism and explain why astronomers suspect such events may be an important factor in the galaxy s history and evolution. Narrate the projected evolution of the Milky Way Galaxy. With what nearby galaxy is our galaxy expected to collide, and when? AST 2010: Chapter 15 11

12 Chapter 16, Part 1: The Family of Galaxies Define surface brightness and explain why galaxies have low surface brightness. Define the notion of zone of avoidance and explain it in terms of the opaqueness of the galactic disk. Identify and distinguish the three main types of galaxies as identified by Hubble and be aware that our Milky Way is a barred spiral. Know which types of galaxies are rich in gas and dust and show evidence of ongoing star formation. Appreciate that the sizes of galaxies vary widely. AST 2010: Chapter 16 12

13 Chapter 16, Part 2: Measuring the Properties of Galaxies Identify and characterize the three main approaches to measuring how far away galaxies are. Discuss the two most important standard candles used for galaxies (Cepheid variables and Type 1a supernovae), their ranges and other limitations. Discuss Hubble s law and understand how it is used for distance measurements to very faraway galaxies. Understand how rotation curves are used to determine the masses of galaxies. Briefly explain how gravitational lensing is used to measure galactic masses and to map out mass distributions in galaxy clusters. Characterize the results of mass measurements and explain why they support the dark matter hypothesis. AST 2010: Chapter 16 13

14 Chapter 16, Part 3: Evolution of Galaxies Know the criteria used to classify clusters as either rich or poor and general demographics of each type. Know the name for the our own galaxy cluster (the Local Group). Is it rich or poor? Discuss the findings from studies of the Hubble Deep Field images as they pertain to galaxy evolution. Understand why collisions between galaxies are expected to be common, and why collisions between stars are spectacularly rare. Discuss the evidence for galactic cannibalism and for collisions and mergers between galaxies. Describe the currently favored model of galaxy evolution. AST 2010: Chapter 16 14

15 Chapter 17, Part 1: Active Galactic Nuclei Define and characterize what is meant by an active galactic nucleus. Characterize and distinguish Seyfert galaxies from Radio galaxies. What properties do they have in common and how do they differ? Be aware that there are objects that fit the definitions of both. Define quasar and identify their commonalities and differences with/from Seyfert and radio galaxies. Characterize especially the luminosity and distance of quasars. How do we know they are so luminous? Be aware that the radiation coming from AGNs has the characteristics of synchrotron radiation. Explain how we know that quasars are so small. How does the fluctuation time of an object s brightness imply a limit on its size? AST 2010: Chapter 17 15

16 Chapter 17, Part 2: Supermassive Black Holes Know the current leading hypothesis for the energy source of AGNs: accretion disk around a supermassive black hole in the core of a galaxy. Be able to explain why astronomers have ruled out ordinary stars or neutron stars. Also identify the evidence for compact massive objects at the cores of most galaxies. Be aware of the correlation between SMBH mass and bulge mass. Explain why the SMBHs inside modern galaxies are no longer active, and be aware that collisions between galaxies are thought to be capable of reactivating them. AST 2010: Chapter 17 16

17 Chapter 18, Part 1: Introduction to the Universe Define and explain the meaning of cosmology. Understand Hubble s law as a consequence of expanding space. Explain the expansion redshift in terms of General Relativity: stretching of light waves by expansion of space. Define the Cosmological Principle. Define and explain the meaning of the Hubble time: the age of the Universe assuming that the rate of expansion has been constant since the beginning. Explain what Olbers paradox is and understand how modern cosmology resolves it. Define and distinguish the concepts of cosmic horizon and visible universe. AST 2010: Chapter 18 17

18 Chapter 18, Part 2: The Big Bang Theory Know the three main predictions of the Big Bang Theory. Define primordial or Big Bang nucleosynthesis and know that only H and He plus trace Li could have formed during the first few minutes of the Universe. Know that the observed abundances of H and He are consistent with the theory. Be aware that the early Universe was opaque to radiation, and the significance of the Recombination Era. Define the Cosmic Microwave Background and understand why it has a temperature of ~3 K today. Be aware that the CMB isn t perfectly isotropic (i.e. uniform over the sky). AST 2010: Chapter 18 18

19 Chapter 18, Part 3: Space and Time; Matter and Energy Define intrinsic curvature, be comfortable with the idea of curved space, and know how curvature affects the relationship between distance, linear size, and observed angular size Define the critical density ρ c = density of matter in a flat universe, and minimum density for universe to collapse back assuming gravity determines the Universe s fate ( Geometry is destiny ). Know that observed abundances of deuterium and lithium fix the density of ordinary matter at 0.04 ρ c. Know that CMB fluctuations imply that the Universe is flat. Understand the implications of large scale structure and early galaxy formation: dark matter, and know that WIMPs are the currently favored candidate for what DM is made of. AST 2010: Chapter 18 19

20 Chapter 18, Part 4: Twenty- First Century Cosmology Appreciate the age problem : if geometry is destiny, with H = 70 km/s/mpc, globular clusters seem to be older than the Universe. Appreciate the missing mass problem : not enough gravity from ordinary matter plus dark matter to make the universe flat. Understand the implications of the Type Ia supernova measurements: expansion is accelerating. Know the properties of hypothetical Dark Energy: positive density, negative (repulsive) gravity, and appreciate how Dark Energy can cause the expansion to accelerate. Appreciate how DE resolves both the age problem and the missing mass problem AST 2010: Chapter 18 20