Astronomy Chapter Thirteen
- 1.
Degeneracy pressure is the source of the pressure that stops the crush of gravity in all the following except:
- A.
A brown dwarf.
- B.
A white dwarf.
- C.
A neutron star.
- D.
A very massive main-sequence star.
- E.
The central core of the Sun after hydrogen fusion ceases but before helium fusion begins.
Correct Answer
D. A very massive main-sequence star. -
- 2.
White dwarfs are so called because
- A.
They are both very hot and very small.
- B.
They are the end-products of small, low-mass stars.
- C.
They are the opposite of black holes.
- D.
It amplifies the contrast with red giants.
- E.
They are supported by electron degeneracy pressure.
Correct Answer
A. They are both very hot and very small. -
- 3.
A teaspoonful of white dwarf material on Earth would weigh
- A.
The same as a teaspoonful of Earth-like material.
- B.
About the same as Mt. Everest.
- C.
About the same as the earth.
- D.
A few tons.
- E.
A few million tons.
Correct Answer
D. A few tons. -
- 4.
Which of the following is closest in mass to a white dwarf?
- A.
The Moon
- B.
Earth
- C.
Jupiter
- D.
The Sun
Correct Answer
D. The Sun -
- 5.
What is the ultimate fate of an isolated white dwarf?
- A.
It will cool down and become a cold black dwarf.
- B.
As gravity overwhelms the electron degeneracy pressure, it will explode as a nova.
- C.
As gravity overwhelms the electron degeneracy pressure, it will explode as a supernova.
- D.
As gravity overwhelms the electron degeneracy pressure, it will become a neutron star.
- E.
The electron degeneracy pressure will eventually overwhelm gravity and the white dwarf will slowly evaporate.
Correct Answer
A. It will cool down and become a cold black dwarf. -
- 6.
Suppose a white dwarf is gaining mass because of accretion in a binary system. What happens if the mass someday reaches the 1.4-solar-mass limit?
- A.
The white dwarf undergoes a catastrophic collapse, leading to a type of supernova that is somewhat different from that which occurs in a massive star but is comparable in energy.
- B.
The white dwarf, which is made mostly of carbon, suddenly becomes much hotter in temperature and therefore is able to begin fusing the carbon. This turns the white dwarf back into a star supported against gravity by ordinary pressure.
- C.
The white dwarf immediately collapses into a black hole, disappearing from view.
- D.
A white dwarf can never gain enough mass to reach the limit because a strong stellar wind prevents the material from reaching it in the first place.
Correct Answer
A. The white dwarf undergoes a catastrophic collapse, leading to a type of supernova that is somewhat different from that which occurs in a massive star but is comparable in energy. -
- 7.
What kind of pressure supports a white dwarf?
- A.
Neutron degeneracy pressure
- B.
Electron degeneracy pressure
- C.
Thermal pressure
- D.
Radiation pressure
- E.
All of the above
Correct Answer
B. Electron degeneracy pressure -
- 8.
What is the upper limit to the mass of a white dwarf?
- A.
There is no upper limit.
- B.
There is an upper limit, but we do not yet know what it is.
- C.
2 solar masses
- D.
1.4 solar masses
- E.
1 solar mass
Correct Answer
D. 1.4 solar masses -
- 9.
How does a 1.2-solar-mass white dwarf compare to a 1.0-solar-mass white dwarf?
- A.
It has a larger radius.
- B.
It has a smaller radius.
- C.
It has a higher surface temperature.
- D.
It has a lower surface temperature.
- E.
It is supported by neutron, rather than electron, degeneracy pressure.
Correct Answer
B. It has a smaller radius. -
- 10.
Which of the following is closest in size (radius) to a white dwarf?
- A.
The earth
- B.
A small city
- C.
A football stadium
- D.
A basketball
- E.
The Sun
Correct Answer
A. The earth -
- 11.
After a massive-star supernova, what is left behind?
- A.
Always a white dwarf
- B.
Always a neutron star
- C.
Always a black hole
- D.
Either a white dwarf or a neutron star
- E.
Either a neutron star or a black hole
Correct Answer
E. Either a neutron star or a black hole -
- 12.
A teaspoonful of neutron star material on Earth would weigh
- A.
About the same as a teaspoonful of Earth-like material.
- B.
A few tons.
- C.
More than Mt. Everest.
- D.
More than the Moon.
- E.
More than the earth.
Correct Answer
C. More than Mt. Everest. -
- 13.
Which of the following is closest in size (radius) to a neutron star?
- A.
The earth
- B.
A city
- C.
A football stadium
- D.
A basketball
- E.
The Sun
Correct Answer
B. A city -
- 14.
From an observational standpoint, what is a pulsar?
- A.
A star that slowly changes its brightness, getting dimmer and then brighter with a period of anywhere from a few hours to a few weeks
- B.
An object that emits flashes of light several times per second or more, with near perfect regularity
- C.
An object that emits random "pulses" of light that sometimes occur only a fraction of a second apart and other times stop for several days at a time
- D.
A star that changes color rapidly, from blue to red and back again
Correct Answer
B. An object that emits flashes of light several times per second or more, with near perfect regularity -
- 15.
What causes the radio pulses of a pulsar?
- A.
The star vibrates.
- B.
As the star spins, beams of radio radiation sweep through space. If one of the beams crosses the earth, we observe a pulse.
- C.
The star undergoes periodic explosions of nuclear fusion that generate radio emission.
- D.
The star's orbiting companion periodically eclipses the radio waves emitted by the main pulsar.
- E.
A black hole near the star absorbs energy and re-emits it as radio waves.
Correct Answer
B. As the star spins, beams of radio radiation sweep through space. If one of the beams crosses the earth, we observe a pulse. -
- 16.
How does a black hole form from a massive star?
- A.
During a supernova, if a star is massive enough for its gravity to overcome neutron degeneracy of the core, the core will be compressed until it becomes a black hole.
- B.
Any star that is more massive than 8 solar masses will undergo a supernova explosion and leave behind a black-hole remnant.
- C.
If enough mass is accreted by a white-dwarf star so that it exceeds the 1.4-solar-mass limit, it will undergo a supernova explosion and leave behind a black-hole remnant.
- D.
If enough mass is accreted by a neutron star, it will undergo a supernova explosion and leave behind a black-hole remnant.
- E.
A black hole forms when two massive main-sequence stars collide.
Correct Answer
A. During a supernova, if a star is massive enough for its gravity to overcome neutron degeneracy of the core, the core will be compressed until it becomes a black hole. -
- 17.
Which of the following statements about black holes is not true?
- A.
If you watch someone else fall into a black hole, you will never see him or her cross the event horizon. However, he or she will fade from view as the light he or she emits (or reflects) becomes more and more redshifted.
- B.
If we watch a clock fall toward a black hole, we will see it tick slower and slower as it falls nearer to the black hole.
- C.
A black hole is truly a hole in spacetime, through which we could leave the observable universe.
- D.
If the Sun magically disappeared and was replaced by a black hole of the same mass, the earth would soon be sucked into the black hole.
- E.
If you fell into a black hole, you would experience time to be running normally as you plunged rapidly across the event horizon.
Correct Answer
D. If the Sun magically disappeared and was replaced by a black hole of the same mass, the earth would soon be sucked into the black hole. -
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