Name: 
 

Einstein's Universe. Exam 2



Completion
Complete each sentence or statement.
 

 1. 

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

 

 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. 

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

 

 5. 

Electrons moving in a strong magnetic field emit _______________ radiation.
 

 

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

 6. 

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

 7. 

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

 8. 

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

 9. 

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

 10. 

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

 11. 

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

 12. 

A Type II supernova produces a planetary nebula.
 

 13. 

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

 14. 

To whether the compact object in an X-ray binary is a neutron star or a black hole, we must find the temperature of the compact object.
 

 15. 

Planetary nebulae are sites of planet formation.
 

 16. 

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

 17. 

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

 18. 

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

 19. 

The sun will eventually become a supernova.
 

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

 20. 

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

 21. 

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
 

 22. 

A nova is almost always associated with
a.
a star undergoing helium flash.
b.
a very massive star.
c.
a white dwarf in a close binary system.
d.
a very young star.
e.
a solar like star that has exhausted its hydrogen and helium.
 

 23. 

Synchrotron radiation is produced by
a.
helium flash.
b.
cold hydrogen atoms in space.
c.
objects with temperatures below 10,000 K.
d.
the collapsing cores of massive stars.
e.
high-velocity electrons moving through a magnetic field.
 

 24. 

The diagram below shows a light curve from a supernova. How many days after maximum light did it take for the supernova to decrease in brightness by a factor of 100?

eu_exam_2_web__files/i0270000.jpg
a.
250
b.
150
c.
100
d.
25
e.
50
 

 25. 

The Schwarzschild radius of a 2 Meu_exam_2_web__files/i0280000.jpg black hole is approximately
a.
2 km.
b.
36 km.
c.
6 km.
d.
4 km.
e.
12 km.
 

 26. 

Although neutron stars are very hot, they are not easy to locate because
a.
solid neutron material cannot radiate photons.
b.
they have small surface areas.
c.
light does not escape from their event horizon.
d.
they are only found in other galaxies.
e.
most lie beyond dense dust clouds.
 

 27. 

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

 28. 

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.
underground counts from solar neutrinos.
d.
calculation of models of core collapse.
e.
the detection of neutrinos from the supernova of 1987.
 

 29. 

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, & IV
b.
I & III
c.
II, III, & IV
d.
I & IV
e.
I, II, III, & IV
 

 30. 

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

 31. 

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

 32. 

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

 33. 

Stars with masses between 0.4 Meu_exam_2_web__files/i0360000.jpg and 4 Meu_exam_2_web__files/i0360001.jpg
a.
produce type-I supernovae after they exhaust their nuclear fuels.
b.
undergo thermonuclear fusion of hydrogen, but never get hot enough to ignite helium.
c.
undergo thermonuclear fusion of hydrogen and helium, but never get hot enough to ignite carbon.
d.
undergo carbon detonation.
e.
produce type-II supernovae after they exhaust their nuclear fuels.
 

 34. 

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

 35. 

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

 36. 

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

 37. 

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.
 

 38. 

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

 39. 

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

 40. 

The Chandrasekhar limit tells us that
a.
white dwarfs must contain more than 1.4 solar masses.
b.
stars with a mass less than 0.5 solar masses will not go through helium flash.
c.
neutron stars of more than 3 solar masses are not stable.
d.
not all stars will end up as white dwarfs.
e.
accretion disks can grow hot through friction.
 

 41. 

If the Schwarzschild radius of a black hole is approximately 75 km. determine its mass.
a.
20 Meu_exam_2_web__files/i0440000.jpg
b.
105 Meu_exam_2_web__files/i0440001.jpg
c.
25 Meu_exam_2_web__files/i0440002.jpg
d.
15 Meu_exam_2_web__files/i0440003.jpg
e.
None of the above
 

 42. 

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 Meu_exam_2_web__files/i0450000.jpg.
c.
looking for pulsars with periods less than one millisecond.
d.
searching for large spherical regions from which no light is detected.
 

 43. 

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

 44. 

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

 45. 

The density of a neutron star is
a.
about the same as an atomic nucleus.
b.
smaller than expected because the magnetic field is so strong.
c.
about the same as that of a white dwarf.
d.
about the same as that of the sun.
e.
about the same as a water molecule.
 

 46. 

A neutron star is expected to spin rapidly because
a.
they have high densities.
b.
they have high temperatures.
c.
they conserved angular momentum when they collapsed.
d.
they have high orbital velocities.
e.
the energy from the supernova explosion that formed them made them spin faster.
 

 47. 

A type-II supernova
a.
is the result of helium flash.
b.
occurs when a white dwarf's mass exceeds the Chandrasekhar limit.
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
 

 48. 

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, & III
b.
I, II, III, IV, & V
c.
I & IV
d.
I, III, & V
e.
I, II, III, & V
 

 49. 

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

 50. 

If the theory that novae occur in close binary systems is correct, then novae should
a.
not occur in old star clusters.
b.
repeat after some interval.
c.
produce synchrotron radiation.
d.
all be visual binaries.
e.
occur in regions of star formation.
 



 
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