Name: 
 

Stars & Galaxies:  EXAM 3



Completion
Complete each sentence or statement.
 

 1. 

A(n) _______________ periodically emits large amounts of x-ray radiation as material accretes around a neutron star or black hole.
 

 

 2. 

A(n) _______________ is a rapidly spinning neutron star that accelerates charged particles near the poles of its magnetic field.
 

 

 3. 

The _______________ of a black hole is the radius from the black hole at which the escape velocity is equal to the speed of light.
 

 

 4. 

_______________ are caused by periodic eruptions in the helium fusion shell and may provide the energy to eject the material that forms a planetary nebula.
 

 

 5. 

A(n) _______________ is the sudden expulsion of the outer layers of a moderate mass star that has a dormant carbon core.
 

 

 6. 

A rotating black hole is referred to as a(n) _______________ black hole.
 

 

 7. 

Material within the _______________ of a rotating black hole is forced to orbit the black hole due to the curvature of space-time, but it could still escape the gravitational pull of the black hole.
 

 

 8. 

The maximum mass of a white dwarf is _______________ solar masses.
 

 

 9. 

Electrons moving in a strong magnetic field emit _______________ radiation.
 

 

 10. 

Most stars generate their energy by the thermonuclear fusion of _______________ to form _______________.
 

 

True/False
Indicate whether the sentence or statement is true or false.
 

 11. 

Once a star ejects a planetary nebula, it becomes a white dwarf.
 

 12. 

The event horizon marks the boundary within which the density is roughly the same as that of the atomic nucleus.
 

 13. 

The Orion region contains young main sequence stars and an emission nebula, but the original molecular cloud they formed out of has been dispersed.
 

 14. 

Synchrotron radiation occurs when high speed electrons move through a magnetic field.
 

 15. 

The sun makes most of its energy by the CNO cycle.
 

 16. 

Stars less massive than 0.4 solar mass never become giant stars.
 

 17. 

T Tauri stars are believed to be young, high mass main sequence stars.
 

 18. 

Neutron stars have densities roughly the same as that of the atomic nucleus.
 

 19. 

A Type II supernova produces a planetary nebula.
 

 20. 

If the accretion disk around a black hole emits X rays outside the event horizon, the X rays can escape.
 

 21. 

No known white dwarf has a mass greater than the Chandrasekhar limit.
 

 22. 

Planetary nebulae are sites of planet formation.
 

 23. 

Pulsars could not be pulsating stars because the pulses are too short.
 

 24. 

Nuclear fusion in stars is controlled by the dependence of density on mass.
 

 25. 

Many pulsars have periods that are gradually increasing as the spinning neutron stars lose energy.
 

 26. 

Neutron stars were first discovered in the 1930's.
 

 27. 

Some young star clusters contain large numbers of T Tauri stars.
 

 28. 

Hydrostatic equilibrium refers to the balance between weight and pressure.
 

 29. 

Energy flows by radiation or convection inside stars but almost never by conduction.
 

 30. 

A nova destroys the star and leaves behind a white dwarf.
 

 31. 

The sun will eventually become a supernova.
 

 32. 

Ninety percent of all stars fuse helium and lie on the main sequence.
 

 33. 

Because massive stars have more gravitational energy than the sun, they can fuse heavier nuclear fuels.
 

 34. 

Theory predicts that neutron stars may not exceed 3 solar masses.
 

 35. 

The sun has a core in which energy travels outward primarily by radiation.
 

 36. 

Type II supernovae are believed to occur when the core of a massive star collapses.
 

 37. 

We expect neutron stars to spin rapidly because they conserve angular momentum.
 

 38. 

An accretion disk can grow hot enough to radiate X rays.
 

Multiple Choice
Identify the letter of the choice that best completes the statement or answers the question.
 

 39. 

The lowest-mass stars cannot become giants because
a.
they do not contain helium.
b.
they rotate too slowly.
c.
they cannot heat their centers hot enough.
d.
they contain strong magnetic fields.
e.
they never use up their hydrogen.
 

 40. 

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.
 

 41. 

The carbon-nitrogen-oxygen cycle
a.
operates at a slightly lower temperature than the proton-proton chain.
b.
is most efficient in a star less massive than the sun.
c.
occurs when carbon and oxygen combine to form nitrogen, which produces energy.
d.
produces the energy responsible for bipolar flows.
e.
combines four hydrogen nuclei to form one helium nucleus, which produces energy.
 

 42. 

_______________ occurs when most of the material collapsing to form a protostar has fallen into a disk around the star, and a strong wind from the warm protostar ejects material from its poles.
a.
An emission nebula
b.
Hydrostatic equilibrium
c.
The proton-proton chain
d.
The thermonuclear fusion of hydrogen
e.
A bipolar flow
 

 43. 

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 surround a planet
 

 44. 

A pulsar requires that a neutron star

I.
rotate rapidly.
II.
have a radius of at least 10 km.
III.
have a strong magnetic field.
IV.
rotate on an axis that is different from the axis of the magnetic field.
a.
I & III
b.
I & IV
c.
II, III, & IV
d.
I, III, & IV
e.
I, II, III, & IV
 

 45. 

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.
 

 46. 

Synchrotron radiation is produced
a.
in planetary nebulae.
b.
by red dwarfs.
c.
by massive stars as their iron core collapses.
d.
in supernova remnants.
e.
by neutrinos
 

 47. 

None of the pulsars emit visible light because
a.
pulsars are too hot to emit visible light.
b.
pulsars contain black holes that won't let visible light escape.
c.
the gravitational field of a pulsar is so great that the visible light emitted is red shifted.
d.
pulsars are too far away for the visible light to be bright enough to be detected at Earth.
e.
The premise is false. A few pulsars are known to emit visible light pulses.
 

 48. 

Stars with masses between 0.4 Msgc_exam_3_web_files_files/i0510000.jpg and 4 Msgc_exam_3_web_files_files/i0510001.jpg
a.
undergo thermonuclear fusion of hydrogen and helium, but never get hot enough to ignite carbon.
b.
undergo thermonuclear fusion of hydrogen, but never get hot enough to ignite helium.
c.
produce type-I supernovae after they exhaust their nuclear fuels.
d.
produce type-II supernovae after they exhaust their nuclear fuels.
e.
undergo carbon detonation.
 

 49. 

Cygnus X-1 and LMC X-3 are black holes if the masses of the unseen companions are
a.
less than 5 solar masses.
b.
more than 5 solar masses.
c.
between 0.4 and 1.4 solar masses.
d.
less than 0.4 solar masses
e.
not larger than the masses of the stars that we can see.
 

 50. 

Massive stars cannot generate energy through iron fusion because
a.
iron fusion requires very high density.
b.
stars contain very little iron.
c.
no star can get hot enough for iron fusion.
d.
iron is the most tightly bound of all nuclei.
e.
massive stars supernova before they create an iron core.
 

 51. 

A supernova remnant is expanding in radius at the rate of 0.5 seconds of arc per year. Doppler shifts show that the velocity of expansion is 5700 km/sec. How far away is the supernova remnant?
a.
1140 pc
b.
11,400 km
c.
5700 pc
d.
24 pc
e.
2400 pc
 

 52. 

The proton-proton chain needs high temperature because
a.
of the ground state energy of the hydrogen atom.
b.
of the presence of helium atoms.
c.
the protons must overcome the Coulomb barrier.
d.
of the need for low density.
e.
the neutrinos carry more energy away than the reaction produces.
 

 53. 

At extremely high densities and temperatures, electrons can be forced to fuse with protons. This reaction produces
a.
hydrogen.
b.
Helium and energy.
c.
degenerate electrons.
d.
neutrons and neutrinos
e.
large amounts of radio radiation.
 

 54. 

The Schwarzschild radius of a 2 Msgc_exam_3_web_files_files/i0570000.jpg black hole is approximately
a.
6 km.
b.
4 km.
c.
2 km.
d.
12 km.
e.
36 km.
 

 55. 

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.
 

 56. 

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.
 

 57. 

The escape velocity of an object depends on

I.
the mass of the object.
II.
the mass of the particle trying to escape.
III.
the radius of the object.
IV.
the distance from the center of the object to the particle trying to escape
V.
the speed of light.
a.
I, II, III, IV, & V
b.
I & IV
c.
I, II, III, & V
d.
I, III, & V
e.
I, & III
 

 58. 

The density of a _______________ is greater than the density of a _______________.
a.
white dwarf; neutron star
b.
neutron star; black hole
c.
pulsar; neutron star
d.
pulsar; white dwarf
e.
white dwarf; black hole
 

 59. 

If the sun produces energy by the proton-proton chain, then the center of the sun must have a temperature of at least
a.
104 K
b.
107 K
c.
1010 K
d.
1013 K
e.
1016 K
 

 60. 

As a white dwarf cools its radius does not change because
a.
pressure due to nuclear reactions in a shell just below the surface keeps it from collapsing.
b.
pressure does not depend on temperature for a white dwarf because the electrons are degenerate.
c.
pressure does not depend on temperature because the white dwarf is too hot.
d.
pressure does not depend on temperature because the star has exhausted all its nuclear fuels.
e.
material accreting onto it from a companion maintains a constant radius.
 

 61. 

The material that accretes onto a neutron star or black hole is expected to emit x-rays because
a.
the material will produce synchrotron radiation because of the strong magnetic field.
b.
hydrogen nuclei begin to fuse and emit high energy photons.
c.
the material will become hot enough that it will radiate most strongly at x-ray wavelengths.
d.
as the material slows down it converts thermal energy to gravitational potential energy.
e.
none of the above
 

 62. 

What is the escape velocity from the surface of a neutron star with a mass of 2 Msgc_exam_3_web_files_files/i0650000.jpg and a radius of 10 km?
a.
5.3sgc_exam_3_web_files_files/i0650001.jpg1016 m/sec
b.
1.6sgc_exam_3_web_files_files/i0650002.jpg108 km/sec
c.
2.3sgc_exam_3_web_files_files/i0650003.jpg108 m/sec
d.
2.3sgc_exam_3_web_files_files/i0650004.jpg108 km/sec
e.
3.0sgc_exam_3_web_files_files/i0650005.jpg108 m/sec
 

 63. 

_______________ is the thermonuclear fusion of hydrogen to form helium operating in the cores of massive stars on the main sequence.
a.
The CNO cycle
b.
The proton-proton chain
c.
Hydrostatic equilibrium
d.
The neutrino process
e.
none of the above
 

 64. 

In the proton-proton chain
a.
no neutrinos are produced.
b.
energy is released because a helium nucleus has a greater mass than a hydrogen nucleus.
c.
no photons are produced.
d.
carbon serves as a catalyst for the nuclear reaction.
e.
energy is produced in the form of gamma rays and the velocity of the created nuclei.
 

 65. 

The event horizon
a.
is believed to be a singularity.
b.
is a crystalline layer.
c.
has a radius equal to the Schwarzschild radius.
d.
marks the inner boundary of a planetary nebula.
e.
is located at the point where synchrotron radiation is created around a pulsar.
 

 66. 

Suppose that a planetary nebula is 0.5 parsecs in diameter and expanding at 20 km/s. How old is it? (Hint: 1 pc = 3.1sgc_exam_3_web_files_files/i0690000.jpg1013 km.)
a.
25,000 years
b.
12,000 years
c.
6,000 years
d.
49,000 years
e.
100,000 years
 

 67. 

The central cores of massive main sequence stars
a.
produce energy by the proton-proton chain.
b.
have a very low opacity.
c.
transmit energy outward by convection.
d.
burn their nuclear fuels more slowly than low mass main sequence stars.
e.
have lower temperatures than the central cores of low mass main sequence stars.
 

 68. 

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.
 

 69. 

A rotating black hole
a.
will produce a pulsar.
b.
will have a stronger gravitational field than a non-rotating black hole.
c.
is known as a Schwarzschild black hole.
d.
causes objects near it to produce large amounts of radio energy.
e.
possesses an ergosphere that lies just beyond the Schwarzschild radius.
 

 70. 

As material flows into a black hole
a.
the material will experience time dilation.
b.
the material will become hotter.
c.
the material will produce an absorption spectrum.
d.
the material will increase in mass.
e.
a and b
 

 71. 

A planetary nebula
a.
produces an absorption spectrum.
b.
produces an emission spectrum.
c.
is contracting to form planets.
d.
is contracting to form the star.
e.
is the result of carbon detonation in a 1 Msgc_exam_3_web_files_files/i0740000.jpg.
 

 72. 

Pulsars are believed to slow down because
a.
they are converting energy of rotation into radiation.
b.
they are dragging companion stars around in their magnetic field.
c.
of friction with the interstellar medium.
d.
of conservation of angular momentum.
e.
their mass is decreasing.
 

 73. 

In A.D. 1054, Chinese astronomers observed the appearance of a new star, whose location is now occupied by
a.
a globular cluster.
b.
a planetary nebulae.
c.
a white dwarf.
d.
a young massive star.
e.
a supernova remnant.
 

 74. 

Millisecond pulsars that are very old are
a.
believed to be the result of mass transfer from a companion that increases the mass of the pulsar.
b.
all single objects.
c.
not spinning as rapidly as they seem because they have four hot spots that produce the flashes.
d.
x-ray binaries.
e.
gamma-ray bursters.
 

 75. 

A typical planetary nebula will be visible for about
a.
50 years.
b.
500 years.
c.
50,000 years.
d.
5,000,000 years.
e.
5 billion years.
 

 76. 

Protostars are difficult to observe because
a.
the protostar stage is very short.
b.
they are surrounded by cocoons of gas and dust.
c.
they radiate mainly in the infrared.
d.
all of the above
e.
they are all so far away that the light hasn't reached us yet.
 

 77. 

The region of the sun just below the photosphere
a.
is undergoing thermonuclear fusion using the proton-proton chain.
b.
is undergoing thermonuclear fusion using the CNO cycle.
c.
is transporting energy to the photosphere by convection.
d.
is not in hydrostatic equilibrium.
e.
a and c above
 

 78. 

Pulsars cannot be spinning white dwarfs because
a.
white dwarfs are not that common.
b.
white dwarfs are not dense enough.
c.
white dwarfs do not have magnetic fields.
d.
a white dwarf spinning that fast would fly apart.
e.
all of the above
 

 79. 

Which of the following objects is considered to possibly contain a black hole?
a.
The central star of the Crab nebula
b.
The Orion nebula.
c.
LMC X-3
d.
Algol
e.
PSR 1257+12
 

 80. 

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
 

 81. 

We know that the central object in a planetary nebula has a surface temperature of at least _______________ K because the nebula contains large amounts of ionized hydrogen.
a.
5000 K
b.
10,000 K
c.
15,000 K
d.
20,000 K
e.
25,000 K
 

 82. 

An isolated black hole in space would be difficult to detect because
a.
there would be no light source nearby.
b.
it would not be rotating rapidly.
c.
it would be stationary.
d.
very little matter would be falling into it.
e.
there would be very few stars behind it whose light the black hole could block out.
 

 83. 

What causes the outward pressure that balances the inward pull of gravity in a star?
a.
The outward flow of energy.
b.
The opacity of the gas.
c.
The temperature of the gas
d.
The density of the gas
e.
c and d
 

 84. 

Interstellar gas clouds may collapse to form stars if they
a.
have very high temperatures.
b.
encounter a shock wave.
c.
rotate rapidly.
d.
are located near main sequence spectral type K and M stars.
e.
all of the above.
 

 85. 

A white dwarf is composed of
a.
hydrogen nuclei and degenerate electrons.
b.
helium nuclei and normal electrons.
c.
carbon and oxygen nuclei and degenerate electrons.
d.
degenerate iron nuclei.
e.
a helium burning core and a hydrogen burning shell.
 

 86. 

The Helix and Egg nebulae are
a.
supernova remnants.
b.
planetary nebulae.
c.
the result of carbon detonation.
d.
the result of the collapse of the iron core of each star.
e.
nebulae associated with Herbig-Haro objects.
 

 87. 

Glitches are associated with
a.
x-ray bursters.
b.
rapidly rotating black holes.
c.
the collapse of a white dwarf to form a neutron star.
d.
changes in the rotation rate of a pulsar.
e.
planets that orbit pulsars.
 

 88. 

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.
 

 89. 

As material leaves an expanding star and begins to fall into a white dwarf
a.
an accretion disk will form around the white dwarf.
b.
the material will cool off because it begins to move at high velocities.
c.
the material will fall directly onto the surface of the white dwarf.
d.
the white dwarf will produce a type-II supernova.
e.
the white dwarf's radius will increase.
 

 90. 

The search for black holes involves
a.
searching for single stars that emit large amounts of x-rays.
b.
finding x-ray binaries where the compact companion has a mass in excess of 3 Msgc_exam_3_web_files_files/i0930000.jpg.
c.
searching for large spherical regions from which no light is detected.
d.
looking for pulsars with periods less than one millisecond.
 



 
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