Fall 2000 ASTR 1120-001 Review for Quiz 3

The quiz will contain 12 multiple-choice questions, and will be 10 minutes long. The intention is that all material on the quiz (saving matters of logic and common sense) is referred to somewhere here.

Bennett's book, Chapters 15-17, is an excellent resource for most of the questions posed below. Chapter S5 covers quantum mechanics and electron degeneracy.

You can also ask about the answers in the review session at 6-7pm on Monday 16 October in Duane G1B30 (our usual lecture hall).

The quiz will not cover the observational evidence for black holes, since I do not yet know exactly what Mitch Begelman will cover on that subject. That material will be covered on Quiz 4.

  1. Hertzsprung-Russell diagram. The Hertzsprung-Russell diagram was the observational key that unlocked our understanding of the stars at the beginning of the 20th century. You should have a thorough understanding of what an HR diagram is, where stars appear in it, and how they evolve in it. Don't forget Stefan-Boltzmann.

  2. Star Clusters. Why are star clusters useful in studies of the HR diagram? The HR diagrams of different star clusters often look very different. Why? Describe the differences.

  3. Main sequence. What is the main sequence? What is it a sequence of?

  4. So Simple a Thing as a Star. The structure and evolution of stars is simpler to understand scientifically than, for example, human beings. Why?

  5. Stellar evolution. We focused on the evolution (a) of a star like the Sun, and (b) of a massive star (greater than about 8 solar masses). Draw the evolution of these stars on an HR diagram, and label the chief events in their lives.

  6. Gravitational Energy. At the beginning of this course we discussed the great principle that when a gravitating system loses energy, it heats up, and we mentioned one example ¾ how a protostar gets hot enough to ignite hydrogen. We have now encountered several other examples. What are they, and what happens specifically in each case? For example, what role does gravitational energy play: (a) when a main sequence star exhausts hydrogen at its core? (b) when a core collapse supernova occurs? (c) in heating the material in an accretion disk up to x-ray emitting temperatures as it swirls on to a neutron star or black hole?

  7. Quantum Mechanics. According to quantum mechanics, all particles are also waves, with a wavelength inversely proportional to their momentum, and a frequency proportional to their energy. Particles also have spin, a bit like a gyroscope, so they know about direction in space. Particles such as electrons satisfy an `exclusion principle': two electrons cannot occupy the same place simultaneously.

  8. Electron Degeneracy. Electron degeneracy is a quantum mechanical effect that arises because electrons are waves, and they do not like to be packed closer than one wavelength. The fact that the outer electrons of solid metals are electron degenerate is what gives metals their characteristic metallic properties of high conductivity and reflectivity. Electron degeneracy provides the pressure support for white dwarfs and the cores of red giant stars (for stars less massive than about 3 suns). Electron degeneracy plays a crucial role in the Helium flash, and in supernovae of both Types. How does electron degeneracy solve Eddington's paradox: `If a star always grows hotter when it loses energy, how can it ever cool down?'

  9. Helium flash. What is the Helium flash? When does it happen? What happens? Why does it occur? What does helium-burning produce that is crucial to the existence of life?

  10. Red Giant. What is a red giant? What is it made of? What is happening at its center? Red giants typically have strong stellar winds; what does the wind do to the red giant? Are red giants necessarily more massive than main sequence stars? Are they necessarily older? Are they necessarily larger? Are they necessarily cooler?

  11. White Dwarf. What is a white dwarf? What is the observational evidence for their existence? What pressure holds it up against gravity? What happens as the mass of a white dwarf increases, say because a binary companion is losing material on to the white dwarf?

  12. Planetary Nebula. What is a planetary nebula? What is the connection between a red giant, a planetary nebula, and a white dwarf?

  13. Chandrasekhar Limit. What is the Chandrasekhar Limit? What role does the Chandrasekhar Limit play in each of the two Types of Supernova?

  14. Type Ia supernova. What observational evidence suggests that Type I (definition: spectrum does not contain H lines) supernovae represent the explosion of a white dwarf? [Note: actually it's just Type Ia supernovae that represent the explosion of a white dwarf; it is now recognized that some Type I supernovae, classified Type Ib and Type Ic, are core-collapse supernovae in which the massive star has lost its hydrogen envelope in a wind.] Why does the light curve (the brightness of the supernova as it changes with time) suggest that the light is powered by the radioactive decay of Nickel 56? What causes the white dwarf to explode? What is the source of the energy of the explosion? Does the supernova leave behind any part of the star?

  15. Type II supernova. What observational evidence suggests that Type II (definition: spectrum contains H lines) supernovae represent the explosion of massive stars? Describe the sequence of events inside a star more massive than about 8 solar masses which is thought to lead up to a supernova. What powers the explosion? The core of the star is made of iron just before it collapses. Why iron? What stops the collapse of the core? The electrons and protons of the iron core combine into neutrons, emitting in the process what kind of particle? What is the source of the energy of the explosion? Does the supernova leave behind any part of the star?