Chap 14 Questions
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York University *
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Course
1740
Subject
Astronomy
Date
Apr 3, 2024
Type
docx
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Review Questions
1.
What is degeneracy pressure, and how is it important to white dwarfs and
neutron stars? What is the difference between
electron degeneracy pressure
and
neutron degeneracy pressure
?
2.
Describe the mass, size, and density of a typical white dwarf. How does the size of a white dwarf depend on its mass?
3.
What happens to the electron speeds in a more massive white dwarf, and
how does this idea lead to the
white dwarf limit
for mass?
4.
What is an
accretion disk
? Describe how an accretion disk can provide a white dwarf with a new source of energy.
5.
What is a
nova
? Describe the process that creates a nova and what a nova looks like.
6.
What processes may cause a
white dwarf supernova
? Observationally, how do we distinguish white dwarf and massive star supernovae?
7.
Describe the mass, size, and density of a typical neutron star. What would
happen if a neutron star came to your hometown?
8.
How do we know that
pulsars
are neutron stars? Are all neutron stars also
pulsars? Explain.
9.
Explain how the presence of a neutron star can make a close binary star system appear to us as an
X-ray binary.
Why do some of these systems appear to us as
X-ray bursters
?
10.
In what sense is a black hole like a hole in the observable universe? Define the
event horizon
and
Schwarzschild radius
.
11.
What do we mean by the
singularity
of a black hole? How do we know
that our current theories are inadequate to explain what happens at the singularity?
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12.
Suppose you are falling into a black hole. How will you perceive the passage of your own time? How will outside observers see time passing for you? Briefly explain why your trip is likely to be lethal.
13.
Why do we think that black holes should sometimes be formed by supernovae? What observational evidence supports the existence of black holes?
14.
What are
gamma-ray bursts
, and how do we think they are produced?
15.
Why can emission of
gravitational waves
lead to mergers of white dwarfs, neutron stars, and black holes? What can result from such mergers? How and when was a black hole merger first detected?
Test Your Understanding
Does It Make Sense?
Decide whether the statement makes sense (or is clearly true) or does not make sense (or is clearly false). Explain clearly; not all these have definitive answers, so your explanation is more important than your chosen answer.
16.
The white dwarf at the center of the Helix Nebula has a mass three times the mass of our Sun.
17.
I observed a white dwarf supernova occurring at the location of an isolated white dwarf (not a member of a binary system).
18.
If you want to find a pulsar, you should look near the remnant of a supernova described by ancient Chinese astronomers.
19.
Scientists have just learned that there is a 10
M
Sun
black hole lurking near Pluto’s orbit.
20.
If your spaceship flew within a few thousand kilometers of a black hole, you and your ship would be rapidly sucked into it.
21.
We can detect black holes with X-ray telescopes because matter falling into a black hole emits X rays after it smashes into the event horizon.
22.
From your point of view, an object falling toward a black hole will
never
cross the event horizon.
23.
The best way to search for black holes is to look for small black circles
in the sky.
24.
Gamma-ray bursts are more likely to be observed in galaxies that are rapidly forming new stars than in galaxies containing only old stars.
25.
Gravitational waves are best observed with the Hubble Space Telescope.
Quick Quiz
Choose the best answer to each of the following. Explain your reasoning with one or more complete sentences.
26.
Which of these objects has the
smallest
radius?
a.
a 1.2
M
Sun
white dwarf
b.
a 0.6
M
Sun
white dwarf
c. Jupiter
27.
Which of these objects has the
largest
radius?
a.
a 1.2
M
Sun
white dwarf
b.
a 1.5
M
Sun
neutron star
c.
a 3.0
M
Sun
black hole
28.
If we see a nova, we know that we are observing
a.
a rapidly rotating neutron star.
b.
a gamma ray–emitting supernova.
c.
a white dwarf in a binary system.
29.
What would happen if the Sun suddenly became a black hole without changing its mass?
a.
The black hole would quickly suck in Earth.
b.
Earth would gradually spiral into the black hole.
c.
Earth would remain in the same orbit.
30.
What would happen to a neutron star with an accretion disk orbiting in a direction opposite to the neutron star’s spin?
a.
Its spin would speed up.
b.
Its spin would slow down.
c.
Its spin would stay the same.
31.
Why do some pairs of neutron stars collide and merge?
a.
Occasionally a neutron star moving through space will collide head-on with another neutron star.
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b.
Gravitational waves from close neutron star binary systems carry away orbital energy and angular momentum.
c.
Electromagnetic waves from pulsars carry away angular momentum.
32.
Which of these binary systems is most likely to contain a black hole?
a.
an X-ray binary containing an O star and another object of equal mass
b.
a binary with an X-ray burster
c.
an X-ray binary containing a G star and another object of equal mass
33.
Viewed from a distance, how would a flashing red light appear as it fell into a black hole?
a.
It would appear to flash more quickly.
b.
Its flashes would appear bluer.
c.
Its flashes would shift to the infrared part of the spectrum.
34.
Which of these black holes exerts the
weakest
tidal forces on an object near its event horizon?
a.
a 10
M
Sun
black hole
b.
a 100
M
Sun
black hole
c.
a 10
6
M
Sun
black hole
35.
Where do gamma-ray bursts tend to come from?
a.
neutron stars in our galaxy
b.
binary systems that also emit X-ray bursts
c.
extremely distant galaxies