Dead and Dying Stars

1. The great width of spectral lines in white dwarfs is due to

a. high temperature

b. high pressure*

c. the presence of a binary companion

d. a high expansion velocity

e. strong gravitational fields.

2. White dwarfs are composed mostly of

a. perfect gases

b. degenerate gases*

c. equal amounts of perfect and degenerate gases

d. hot, solid material.

3. A star with a mass of less than 1.4 solar masses will probably end its life as a

a. white dwarf *

b. neutron star

c. black hole

d. pulsar

4. What keeps a white dwarf from collapsing further?

a. Gravity stops working.

b. The star has become compressed as dense as lead.

c. The high temperature creates pressure.

d. Pressure from electron degeneracy.*

e. None of these.

5. The Chandrasekhar limit tells us that

a. accretion disks can grow hot through friction.

b. neutron stars of more than 3 solar masses are not stable.

c. white dwarfs must contain more than 1.4 solar masses.

d. not all stars will end up as white dwarfs. *

e. stars with a mass less than 0.5 solar masses will not go through helium flash.

6. The fate of a white dwarf is to

a. collapse eventually to become a neutron star

b. eject a shell of material and become a planetary nebula

c. explode as a nova

d. cool until it no longer emits any light.*

7. A planetary nebula is

a. the expelled outer envelope of a medium mass star. *

b. produced by a supernova explosion.

c. produced by a nova explosion.

d. a nebula within which planets are forming.

e. a cloud of hot gas surrounding a planet.

8. A planetary nebula

a. produces an absorption spectrum.

b. produces an emission spectrum. *

c. is contracting to form planets.

d. is contracting to form a star.

e. is the result of carbon detonation in a 1 M star.

9. When the Sun becomes a white dwarf, approximately half its main sequence mass will be left. Where will the rest of the mass have gone?

a. It will have been consumed by nuclear burning.

b. It will be ejected as a planetary nebula.*

c. It will be ejected in a supernova explosion.

d. It will become a black hole.

e. None of these.

10. The Crab nebula is

a. a planetary nebula.

b. a Bok globule.

c. an open cluster.

d. an absorption nebula.

e. supernova remnant. *

11. A Type I supernova is believed to occur when

a. the core of a massive star collapses.

b. carbon detonation occurs.

c. a white dwarf exceeds the Chandrasekhar limit. *

d. the cores of massive stars collapse.

e. neutrinos in a massive star become degenerate and form a shock wave that explodes the star.

12. The theory that the collapse of a massive star's iron core produces neutrinos was supported by

a. the size and structure of the Crab nebula.

b. laboratory measurements of the mass of the neutrino.

c. the brightening of supernovae a few days after they are first visible

d. underground counts from solar neutrinos.

e. the detection of neutrinos from supernova 1987A. *

13. Synchrotron radiation is produced by

a. objects with temperature below 10,000 K.

b. high-velocity electrons moving through a magnetic field. *

c. cold hydrogen atoms in space.

d. the collapsing cores of massive stars.

e. helium flash.

14. Synchrotron radiation is produced

a. in planetary nebulae.

b. by red dwarfs.

c. in massive stars as their iron core collapses.

d. in supernova remnants. *

e. by neutrinos

15. A type-II supernova

a. occurs when a white dwarf's mass exceeds the Chandrasekhar limit.

b. is the result of helium flash.

c. is characterized by a spectrum that shows hydrogen lines.

d. occurs when the iron core of a massive star collapses.

e. c and d *

16. Would you expect the appearance of the Crab Nebula to change in the next 500 years?

a. It will grow bigger.

b. It will diffuse.

c. The filaments will change shape.

d. All of these.*

e. None of these.

17. In view of current theories about supernovae and pulsars, which of the following observations indicates that the Crab pulsar is young?

a. The Crab is rotating the most rapidly of all known pulsars, and since pulsars slow down with age, it must be the youngest.

b. Since we believe the Crab was formed in the supernova explosion of 1054 C.E., this association shows it to have a relatively young age.

c. The Crab nebula is the most compact supernova remnant that is known, indicating it has not had enough time to expand far.

d. All of these.*

e. None of these.

18. A crucial role that supernovae play in the scheme of cosmic evolution is that

a. supernovae are the only source of neutrons

b. some elements heavier than iron are believed to be manufactured chiefly in supernovae *

c. supernovae serve to disperse gas around the galaxy so that new stars can form

d. supernovae are a major source of light in most galaxies

e. supernovae have always been considered as omens that govern the affairs of man

19. Observations from the Compton Gamma Ray Observatory showed that gamma-ray bursters were located throughout the sky. This told us that

a. the bursts were not produced among stars in our galaxy. *

b. neutron stars are very common.

c. the bursts are not associated with neutron stars or black holes.

d. gamma rays are easily produced by very cold material.

e. the bursts are associated with the Big Bang.

20. In A. D. 1054, Chinese astronomers observed the appearance of a new star, whose location is now occupied by

a. a pulsar.

b. a neutron star.

c. a supernova remnant.

d. all of the above*

e. a and b

21. The core of a star remaining after the supernova event may become a

a. quasar

b. white dwarf

c. neutron star*

d. black dwarf

e. planet

22. Which of the following is NOT a general characteristic of a typical neutron star?

a. size about 10-20 km

b. density about 10¹⁷ kg/m³

c. composed mostly of neutrons

d. triple-alpha process going on in core *

e. very strong magnetic field

23. The density of a neutron star is

a. about the same as that of a white dwarf.

b. about the same as that of the sun.

c. about the same as an atomic nucleus. *

d. about the same as a water molecule.

e. smaller than expected because the magnetic field is so strong.

24. The internal properties of a neutron star are most similar to those of a ______ star.

a. main sequence

b. red giant

c. red dwarf

d. white dwarf*

e. solar-type

25. Stellar remnants with masses between 1.4 and 3 solar masses will be

a. white dwarfs

b. neutron stars*

c. black holes

d. planetary nebula.

26. A neutron star is expected to spin rapidly because

a. they conserved angular momentum when they collapsed. *

b. they have high orbital velocities.

c. they have high densities.

d. they have high temperatures.

e. the energy from the supernova explosion that formed them made them spin faster.

27. Although neutron stars are very hot, they are not easy to locate because

a. light does not escape from their event horizon.

b. most lie beyond dense dust clouds.

c. solid neutron material cannot radiate photons.

d. they are only found in other galaxies.

e. they have small surface areas. *

28. Pulsars are probably

a. pulsating white dwarfs

b. pulsating neutron stars

c. rotating white dwarfs

d. rotating neutron stars*

e. rotating black holes.

29. The pulses of radiation received from a pulsar are caused by rapid

a. temperature changes

b. size changes which produce rapid luminosity changes

c. temperature changes which produce rapid luminosity changes

d. changes in the magnetic properties of the star

e. changes in the viewing angle of the magnetic pole.*

30. Which of the following observed properties of pulsars is most important in the inference that pulsars are neutron stars?

a. Pulsars are concentrated in the galactic plane.

b. One binary pulsar has been discovered to date.

c. All pulsars give off radio pulses.

d. The fastest pulsars have periods of less than 1 sec. *

e. The Crab Nebula pulsar has been observed to be pulsing at optical wavelengths.

31. Pulsars are believed to slow down because

a. they are converting energy of rotation into radiation. *

b. they are dragging companions stars around in their magnetic field.

c. of friction with the interstellar medium.

d. of conservation of angular momentum.

e. their mass is decreasing.

32. Why don't all supernova remnants contain pulsars?

a. All supernova remnants do contain pulsars.

b. Some supernova explosions form white dwarfs instead of the neutron stars necessary for pulsars.

c. Pulsars slow down and quite producing the pulses before the supernova remnant dissipates.

d. The pulsar may be tipped so that the beams do not sweep past Earth. *

e. b and c above.

33. The accretion disk surrounding a neutron star is very hot due to compression caused by gravitational forces. In which spectral region will the object emit strongly?

a. x-ray*

b. ultraviolet

c. visual

d. infrared

e. radio.

34. As a massive star collapses, the gravitational field on the stellar surface

a. doubles

b. increases strongly*

c. decreases with the square of the decreasing size

d. remains the same.

35. The Schwarzschild radius of a non-rotating black hole is

a. the main sequence radius

b. the size of a star whose gravitational field does not allow light to escape*

c. the theoretical size of the smallest possible white dwarf

d. the size of a star when it begins hydrogen burning

e. the size of the early protosun.

36. Which of the following is not a fundamental property of a black hole?

a. mass

b. electrical charge

c. temperature*

d. spin or angular momentum

e. all the above are fundamental properties of a black hole.

37. If black holes exist, we might expect them to form

a. from stars that slowly cool off, becoming a cinder

b. from stars whose cores are too massive to allow a neutron star to form when the core collapses *

c. from solar-type stars when they stop giving off light

d. from neutron stars that are less massive than white dwarf stars

38. Why is a black hole blacker than a black piece of paper?
A black piece of paper

a. does not emit radiation in the visible but may emit in other spectral regions.*

b. is red in the infrared region of the spectrum.

c. is violet in the ultraviolet region of the spectrum.

d. All of these.

e. None of these.

39. If you were traveling in space an approached within one of the following limits of a rotating black hole, from which one could you not escape?

a. The photon sphere.

b. The ergosphere.

c. The event horizon.

d. You cannot escape from any of them.*

e. You can escape from all of them.

40. Which of the following lists the objects in order of decreasing mass?

a. neutron star, white dwarf, black hole

b. black hole, neutron star, white dwarf*

c. white dwarf, black hole, neutron star

d. black hole, white dwarf, neutron star

e. they all have approximately the same mass.

41. Light coming from matter approaching a black hole will be

a. strongly redshifted*

b. strongly blueshifted

c. none of the above; there is no spectral shift

d. none of the above; light cannot fall into a black hole.

42. A mass is transferred through the inner Lagrangian point in a binary system toward a white dwarf, the material forms a rapidly growing whirlpool of material known as a(n)

a. accretion disk.*

b. Lagrangian point.

c. Algol paradox.

d. planetary nebula.

e. supernova remnant.

43. A nova is almost always associated with

a. a very massive star.

b. a very young star.

c. a star undergoing helium flash.

d. a white dwarf in a close binary system. *

e. a solar like star that has exhausted its hydrogen and helium.

44. If the theory that novae occur in close binary systems is correct, then novae should

a. produce synchrotron radiation.

b. occur in regions of star formation.

c. not occur in old star clusters.

d. all be visual binaries.

e. repeat after some interval. *

45. What evidence do we have that material is being ejected from novae?

a. We can measure the ejected material's motion from photographs.*

b. Ejected material makes novae bright.

c. There are no other plausible mechanisms for novae.

d. Ejected material is measurable from infrared radiation.

e. None of these.

46. If we see a massive main-sequence star (M > 8 M_¤), what can we assume about its age, relative to most stars?

a. It is younger.*

b. It is about the same age as other stars.

c. It is older.

d. It is older than a red giant.

e. None of these.

47. Which of the following is NOT a characteristic that differentiates novae from supernovae?

a. More energy is released in a supernova than in a nova.

b. Supernova explosions involve most or the entire star, whereas in novae, only the outer part of the star explodes.

c. Novae occur more frequently than supernovae.

d. Supernovae are only seen to occur in binary star systems. *

48. If novae occur in close binary star systems, the source of the nova outburst is

a. the collision of the two stars

b. the infall of matter on a white dwarf star *

c. the explosion of the less highly evolved star

d. the start of helium burning in both stars

49. Why can the precession of an accretion disk that is emitting gas jets at great velocity cause varying Doppler shifts?

a. Because gas jets will be moving in random directions.

b. Because gas jets will be oscillating back and forth.

c. Because precession carries the gas jets around so that they are at differing angles from us.*

d. Because rotating gas jets must give differing Doppler shifts at different points.

e. None of these.

50. Could we detect a black hole that was not part of a binary system?

a. Yes, from x-rays given off by captured gas.

b. Yes, by gravitational effects on other stars.

c. Yes, by point-like brightness distributions.

d. Effects given in a, b, and c might indicate a possible black hole, but it would be difficult to prove.*

e. The only way to detect a black hole is by its effects in a binary system.