Astronomy Chapter Thirteen

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1. What is the upper limit to the mass of a white dwarf?

There is no upper limit.

There is an upper limit, but we do not yet know what it is.

2 solar masses

1.4 solar masses

1 solar mass

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2. 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?

The white dwarf immediately collapses into a black hole, disappearing from view.

3. What kind of pressure supports a white dwarf?

Neutron degeneracy pressure

Electron degeneracy pressure

Thermal pressure

Radiation pressure

All of the above

4. After a massive-star supernova, what is left behind?

Always a white dwarf

Always a neutron star

Always a black hole

Either a white dwarf or a neutron star

Either a neutron star or a black hole

5. A teaspoonful of white dwarf material on Earth would weigh

The same as a teaspoonful of Earth-like material.

About the same as Mt. Everest.

About the same as the earth.

A few tons.

A few million tons.

6. What causes the radio pulses of a pulsar?

The star vibrates.

The star undergoes periodic explosions of nuclear fusion that generate radio emission.

The star's orbiting companion periodically eclipses the radio waves emitted by the main pulsar.

A black hole near the star absorbs energy and re-emits it as radio waves.

7. From an observational standpoint, what is a pulsar?

An object that emits flashes of light several times per second or more, with near perfect regularity

A star that changes color rapidly, from blue to red and back again

8. White dwarfs are so called because

They are both very hot and very small.

They are the end-products of small, low-mass stars.

They are the opposite of black holes.

It amplifies the contrast with red giants.

They are supported by electron degeneracy pressure.

9. Which of the following statements about black holes is not true?

A black hole is truly a hole in spacetime, through which we could leave the observable universe.

10. Which of the following is closest in size (radius) to a white dwarf?

The earth

A small city

A football stadium

A basketball

The Sun

11. What is the ultimate fate of an isolated white dwarf?

It will cool down and become a cold black dwarf.

As gravity overwhelms the electron degeneracy pressure, it will explode as a nova.

As gravity overwhelms the electron degeneracy pressure, it will explode as a supernova.

As gravity overwhelms the electron degeneracy pressure, it will become a neutron star.

The electron degeneracy pressure will eventually overwhelm gravity and the white dwarf will slowly evaporate.

12. Which of the following is closest in mass to a white dwarf?

The Moon

Earth

Jupiter

The Sun

13. Degeneracy pressure is the source of the pressure that stops the crush of gravity in all the following except:

A brown dwarf.

A white dwarf.

A neutron star.

A very massive main-sequence star.

The central core of the Sun after hydrogen fusion ceases but before helium fusion begins.

14. A teaspoonful of neutron star material on Earth would weigh

About the same as a teaspoonful of Earth-like material.

A few tons.

More than Mt. Everest.

More than the Moon.

More than the earth.

15. How does a black hole form from a massive star?

A black hole forms when two massive main-sequence stars collide.

16. Which of the following is closest in size (radius) to a neutron star?

The earth

A city

A football stadium

A basketball

The Sun

17. How does a 1.2-solar-mass white dwarf compare to a 1.0-solar-mass white dwarf?

It has a larger radius.

It has a smaller radius.

It has a higher surface temperature.

It has a lower surface temperature.

It is supported by neutron, rather than electron, degeneracy pressure.

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