Deck 15: Stellar Remnants: White Dwarfs, Neutron Stars, and Black Holes

Question 1

______ are hot compact stars whose mass is comparable to the Sun's and size to Earth's.

A) White dwarfs
B) Neutron stars
C) Pulsars
D) Black holes

Answer 1

White dwarfs

Question 2

Which of the following objects do you expect to find at the center of a planetary nebula?

A) planet
B) neutron star
C) white dwarf
D) black hole

Answer 2

white dwarf

Question 3

A _____ happens when a white dwarf in a binary system accumulates more mass than the Chandrasekhar limit.

A) Nova
B) Type Ia supernova
C) Type II supernova
D) Pulsar
E) None of these choices is correct.

Answer 3

Type Ia supernova

Question 4

This event recurs and happens when one of the companions in the binary system is a white dwarf.

A) Nova
B) Type I supernova
C) Type II supernova
D) Pulsar
E) None of these choices is correct.

Question 5

Which of the following is a remnant of a dying star?

A) white dwarf
B) neutron star
C) black hole
D) All of these choices are correct.

Question 6

The Chandrasekhar limit is the largest ______ a white dwarf can have.

A) speed
B) mass
C) temperature
D) wavelength

Question 7

_______ are remnants of low-mass stars.

A) Neutron stars
B) Pulsars
C) White dwarfs
D) Black holes

Question 8

Type Ia supernovas involve a __________.

A) white dwarf
B) neutron star
C) black hole
D) planetary nebula

Question 9

Compared to the Sun, white dwarfs have higher _____ and lower ___________________.

A) masses; surface temperatures
B) volumes; surface temperatures
C) surface temperatures; luminosities
D) luminosities; surface temperatures

Question 10

White dwarfs have a surface composed of a thin layer of ____________.

A) hydrogen and oxygen
B) hydrogen and helium
C) carbon and oxygen
D) carbon and helium

Question 11

Astronomers use ____________ to determine the magnetic field of white dwarfs.

A) the doppler effect
B) Wien's law
C) conservation of angular momentum
D) the Zeeman splitting of spectral lines

Question 12

Why do white dwarfs have high temperatures?

A) heat left over from their formation
B) chemical reactions on their surfaces
C) nuclear fusion in their cores
D) frictional heating from motions inside the white dwarfs

Question 13

If left in isolation a white dwarf will eventually

A) cool off and become a black dwarf.
B) explode as a type la supernova.
C) form a brown dwarf.
D) become the seed for a new star.

Question 14

A __________ happens when a single high-mass star explodes.

A) Nova
B) Type Ia supernova
C) Type II supernova
D) Pulsar
E) None of these choices is correct.

Question 15

_____ are hot compact remnant stars whose mass is typically between one and several times that of the Sun, but their size is only 10 km or less.

A) White dwarfs
B) Neutron stars
C) Pulsars
D) Black dwarfs

Question 16

This recurring event happens in the case of a binary system in which one of the companions is a neutron star.

A) novae
B) Type I supernovae
C) Type II supernovae
D) X-ray bursts
E) None of these choices is correct.

Question 17

If stars rotate with periods of tens of days, why does a neutron star rotate several to thousands of times a second?

A) When a neutron star collapses, the intensified magnetic field causes it to rotate much more quickly.
B) When a neutron star collapses, its rotation is kicked up by the ejected material from the supernova.
C) When a neutron star collapses, its rotation rate speeds up because of conservation of angular momentum.
D) The collapsing neutron star becomes hot and the fast rotation is the result of thermal energy.

Question 18

Millisecond pulsars rotate about ______ times per second.

A) 10
B) 100
C) 1,000
D) 1 million

Question 19

In comparison to main sequence stars, which of the neutron star properties listed is not considered extreme?

A) magnetic field
B) spin rate
C) density
D) mass

Question 20

The first pulsars were observed using _______ telescopes.

A) optical
B) X-ray
C) infrared
D) radio
E) gamma ray

Question 21

The fast rotation of neutron stars is a consequence of __________________.

A) Wien's law
B) the doppler effect
C) their high temperature
D) the law of conservation of angular momentum

Question 22

Gravitational waves

A) are how pulsars pulse.
B) carry material into black holes.
C) are traveling distortions of space and time.
D) do not carry energy.

Question 23

When a high-mass star's core collapses the star could _________.

A) explode as a supernova
B) become a pulsar
C) become a neutron star
D) become a black hole
E) All of these choices are correct.

Question 24

Why are supernova explosions important for our existence?

A) They heat the interstellar medium and help keep Earth warm.
B) They liberate from the star's core the heavy elements of which we and Earth are made.
C) They destroy wandering stars that might otherwise collide with our Sun.
D) They bathe Earth in X-rays that may have helped life form.
E) They sterilized the young Earth and allowed life to originate by killing off competing bacteria.

Question 25

When a spinning object changes its size, its rotation rate

A) remains the same.
B) always increases.
C) always decreases.
D) increases or decreases, depending on whether it shrinks or expands.

Question 26

The change in rotation rate of a spinning object caused by its size change is a consequence of

A) conservation of magnetic energy.
B) the law of action-reaction.
C) conservation of angular momentum.
D) the special theory of relativity.
E) None of these choices is correct.

Question 27

The law of conservation of angular momentum states that when an object of a fixed mass changes its radius R, its rotation velocity V will change so that

A) V/R = constant.
B) VR = constant.
C) R/V = constant.
D) V²R = constant.
E) R²V = constant.

Question 28

If a spinning object's radius shrinks by a factor of 5, its rotation velocity will

A) get five times faster.
B) get five times slower.
C) remain the same.
D) get 10 times faster.
E) get 25 times faster.

Question 29

The Sun rotates now with a rotation speed of about 2 km/sec. If its radius shrank to the size of Earth, about how fast would it spin?

A) 20 km/sec.
B) 2,000 km/sec.
C) 200 km/sec.
D) 0.2 km/sec.
E) 400 km/sec.

Question 30

A method for identifying a black hole is to

A) observe them directly through the space-based telescopes.
B) look for voids (holes) in the star fields.
C) look for its effect on nearby companions.
D) search for radio waves from the accretion disk.

Question 31

The escape velocity inside a black hole is

A) zero.
B) infinity.
C) unknown.
D) half the speed of light.
E) greater than the speed of light.

Question 32

What is the escape velocity at the event horizon of a black hole?

A) speed of sound
B) supersonic speed
C) speed of light
D) half the speed of light

Question 33

Which of the following can actually escape a black hole?

A) electrons
B) very high energy gamma rays
C) visible light
D) very low energy radio waves
E) None of these choices is correct.

Question 34

The mass of a black hole can be determined by _____________.

A) measuring its volume and density
B) the electromagnetic radiation it emits
C) how rapidly it is spinning
D) applying the modified version of Kepler's Third law, if the black hole is in a binary system

Question 35

The temperature of black holes is estimated to be ______________.

A) hotter than the Sun
B) less than 1 millionth of a degree
C) hotter than 1 million degrees
D) hotter than a white dwarf
E) Black holes do not have temperature.

Question 36

Black holes emit radiation in the form of ______ waves known as Hawking radiation.

A) gravitational
B) electromagnetic
C) seismic
D) nuclear

Question 37

An isolated black hole will

A) eventually suck in all of the universe.
B) implode due to its own gravity.
C) not change in any way.
D) slowly evaporate away through the emission of Hawking radiation.

Question 38

Which of the following elements is NOT produced in a Type Ia supernova?

A) Silicon
B) Nickel
C) Cobalt
D) Iron
E) Neon

Question 39

Why do pulsars "pulse"?

A) They have extremely strong magnetic fields.
B) They have extremely fast rotation rates.
C) Their rotation axis is misaligned with their magnetic field axis.
D) Their surface expands and contracts rapidly, causing changes in brightness.

Question 40

Which of the following elements is NOT produced by neutron star mergers?

A) Silver
B) Gold
C) Uranium
D) Copper
E) Lead

Question 41

The surface temperature of a white dwarf is higher than the surface temperature of the Sun.

Question 42

The more mass a white dwarf has the larger it is.

Question 43

A chunk of material from the interior of a white dwarf would weigh about 100 times more than an Earth rock of the same size.

Question 44

White dwarfs have magnetic fields as much as 100 million times larger than Earth's magnetic field.

Question 45

The interior of a white dwarf behaves like a degenerate gas, i.e., the temperature has little effect on the pressure.

Question 46

Typically, if the mass of a white dwarf increases, the white dwarf shrinks and then explodes if the mass exceeds 1.4 solar masses.

Question 47

The spectral lines of white dwarf stars are redshifted, because their high gravity reduces the energy carried by light escaping from the white dwarf.

Question 48

Nova explosions involve a binary system of a white dwarf and a companion star and can occur in the same system repeatedly.

Question 49

A Type Ia supernova results in the formation of a neutron star.

Question 50

The strong gravitational field of a white dwarf slows down the speed of escaping light, and results in the gravitational redshift.

Question 51

The fast rotation of neutron stars is a consequence of the law of conservation of angular momentum.

Question 52

Neutron stars must have a mass smaller than the Chandrasekhar limit.

Question 53

Pulsars are rotating white dwarfs.

Question 54

A gravitational wave can carry energy away from two very dense objects if they are orbiting each other or collide.

Question 55

If the Sun were instantly replaced by a black hole of the same mass as our Sun, Earth would be sucked into the black hole.

Question 56

A black hole is an object with escape velocity about half the speed of light.