1. Stellar Physics 2 Multiple Choice Questions

2. Test Question Does this quiz work? A. Yes B. No

3. Stellar Physics 2 • 1. Which of the following statements are FALSE? • Low mass stars (<8 Msun) fuse up to carbon. y • High mass stars (≥8 Msun) fuse up to iron and nickel. • Low mass stars (~1 Msun) fuse up to carbon. • High mass stars (>1 Msun) fuse up to iron and nickel.

4. Stellar Physics 2 • 2. Which of the following is an incorrect statement about supernovae? • Supernovae brighten rapidly to ~109 Lsun in about 10 days, then slowly dim over about 100 days. • A supernovae can temporarily outshine its host galaxy. • The energy source of a supernovae is the release of gravitational potential energy by the contraction of the core. • Stars of the Sun’s mass and above will turn into black holes. y

5. Stellar Physics 2 • 3. The Heisenberg uncertainty principle relates what two variables? • Uncertainty in mass and uncertainty in momentum. • Uncertainty in mass and uncertainty in position. • Uncertainty in momentum and uncertainty in position. y • Uncertainty in momentum and uncertainty in time.

6. Stellar Physics 2 • 4. The central pressure required to a body against its own self gravity is given by Pc = ___πGρ2(R2/2). What is the scalar value that needs to be inserted in the blank to complete the expression? • 4/3. y • 5/3. • 7/3. • 1/3.

7. Stellar Physics 2 • 5. What is the Chandrasekhar Mass Limit? • The minimum mass that a white dwarf can be. • The minimum mass that a neutron star can be. • The maximum mass that a white dwarf can be. Y • The maximum mass that a white dwarf can be.

8. Stellar Physics 2 • 6. What is the pressure source in a white dwarf? • Electron degeneracy pressure. y • Neutron degeneracy pressure. • Proton degeneracy pressure. • Gravitational potential energy.

9. Stellar Physics 2 • 7. In a white dwarf, how does degeneracy pressure vary with density? • Pressure varies with density as ρ4/3. • Pressure varies with density as ρ5/3. y • Pressure varies with density as ρ7/3. • Pressure varies with density as 1/ρ.

10. Stellar Physics 2 • 8. Which of the following statements about white dwarfs is FALSE? • They are supported by electron degeneracy pressure. • They are very small but very bright. Y • They have much leftover gravitational energy from collapse so they are very hot. • They have a very high density: ~109 kg m-3.

11. Stellar Physics 2 • 9. How big would a neutron star of a few solar masses be expected to be? • Radius 1km. • Radius 10km. Y • Radius 100km. • Radius 1000km.

12. Stellar Physics 2 • 10. Which of the following statements about neutron stars is true? • Neutron stars are stars with a mass above the Chandrasekhar Mass limit and its electrons have become relativistic. Y • Neutron stars are stars with a mass below the Chandrasekhar Mass limit and its electrons have become relativistic. • Neutron stars are stars with a mass above the Chandrasekhar Mass limit, its electrons are yet to become relativistic. • Neutron stars are stars with a mass below the Chandrasekhar Mass limit, its electrons are yet to become relativistic.

13. Stellar Physics 2 • 11. What is the Oppenheimer-Volkoff Mass Limit? • The critical mass above which neutron degeneracy pressure is unable to support the white dwarf in a stable equilibrium. • The critical mass below which neutron degeneracy pressure is unable to support the neutron star in a stable equilibrium. • The critical mass below which neutron degeneracy pressure is unable to support the white dwarf in a stable equilibrium. • The critical mass above which neutron degeneracy pressure is unable to support the neutron star in a stable equilibrium. y

14. Stellar Physics 2 • 12. In a neutron star, how does degeneracy pressure vary with density? • Pressure varies with density as ρ4/3. • Pressure varies with density as ρ5/3. y • Pressure varies with density as ρ7/3. • Pressure varies with density as 1/ρ.

15. Stellar Physics 2 • 13. How does the radius of a neutron star depend on its mass? • It doesn't - all neutron stars have the same finite radius. • It doesn't - all neutron stars have zero radius (i.e. are point-like). • More massive neutron stars are larger. y • More massive neutron stars are smaller.

16. Stellar Physics 2 • 14. Which of the following statements about neutron stars is FALSE? • They are mostly made up of neutron degenerate matter, with an outer ‘crust’ of white-dwarf-like material. • They have exhausted most of their gravitational potential energy so they are cool. y • They are extremely small. • They are supported by neutron degeneracy pressure.

17. Stellar Physics 2 • 15. The escape velocity is given by Ve = (2GM/R)1/2. Schwarzschild replaced Ve with c and rearranged to find the radius named after him. What does this expression become? • Rs = GM/c2. • Rs = 2GM/c2. y • Rs = GM/c. • Rs = 2GM/c.

18. Stellar Physics 2 • 16. A planet could sit in a stable orbit close to a black hole (outside Rs) without being sucked in, true or false? • True. Y • False.

19. Stellar Physics 2 • 17. Can energy escape a black hole? • No. • Yes. Y • Yes, but who knows where, maybe in a parallel universe.

20. Stellar Physics 2 • 18. What will happen to a 5 solar mass black hole in a dense nebula? • The black hole will not interact with the nearby space at all, so its mass will remain constant. • In-falling matter and radiation will exceed Hawking radiation, so the black hole will grow. • Hawking radiation will exceed in-falling matter and radiation, so the black hole will evaporate. y • None of the above.

21. Stellar Physics 2 • 19. _________ = 1066(M/Msun)3. What is this an expression for and what are its units? • The rate of energy loss for a black hole through Hawking Radiation in J/s. • The time for a black hole to completely evaporate through Hawking Radiation in years. y • The time for a black hole to completely evaporate through Hawking Radiation in seconds. • The rate of energy loss for a black hole through Hawking Radiation in J/year.

22. Stellar Physics 2 • 20. Which of the following is the correct form of the distance modulus formula? • M – m = 5log10d – 5. • m – M = -2.5log10 – 5. • M – m = -2.5log10 – 5. • m – M = 5log10 – 5. y

23. Stellar Physics 2 • 21. Neutron stars do not have a very large angular momentum? • True. • False. y

24. Stellar Physics 2 • 22. In order to calculate the centrifugal break up limit, you need to know an equation for the centripetal acceleration, which of the following is such an equation? • a = ω2r. y • a = ω2/r. • a = ωr. • a = ω/r.

25. Stellar Physics 2 • 23. The plasma making up a collapsing stellar core has a magnetic field, what will happen to the magnetic field lines as the star collapses? • They will move closer together. • They will remain unchanged. y • They will move further apart. • They will disappear.

26. Stellar Physics 2 • 24. What is a pulsar? • It is a neutron star that does not lie in hydrostatic equilibrium and thus pulses in size and luminosity. • It is a neutron star of which the magnetic field pulses in and out thus accelerating a stream of charged particles with each pulse. • It is an asymmetric neutron star (due to an accretion disk), which, as it rotates shows its brighter and then darker side to earth thus giving the appearance of pulsation. • It is a rapidly rotating neutron star with a strong magnetic field at the poles which accelerates charged particles into a beam at either pole. y

27. Stellar Physics 2 • 25. Which of the following statements about observational signatures of black holes are true? • There is strong evidence of both gravitational microlensing and gravitational waves. • There is promising signs of gravitational microlensing but none of gravitational waves yet. y • There is promising signs of gravitational waves but none of gravitational microlensing yet. • There is no evidence at all of either gravitational microlensing or gravitational waves.

28. Stellar Physics 2 • 26. In a degenerate gas of electrons and protons, why can the protons still be non- relativistic even when the electrons have become relativistic? • Protons are positively charged, whereas electrons are negatively charged, so electrons become relativistic first. • Protons are much more massive than electrons, and since both the protons and electrons have the same individual particle momentum the protons move much more slowly. y • Protons individually have less momentum than electrons in a degenerate gas. • They can't - all particles become degenerate at the same point.