Deck 20: White Dwarfs, neutron Stars, and Black Holes

Question 1

Compared to low mass white dwarfs,massive white dwarfs are

A)Smaller and less dense
B)Smaller and denser
C)Larger and denser
D)Larger and less dense

Answer 1

Smaller and denser

Question 2

Which of the following best describes how the appearance of a star changes as it evolves after becoming a white dwarf?

A)It becomes hotter and brighter
B)It becomes hotter and dimmer
C)It becomes cooler and dimmer
D)It becomes cooler and brighter

Answer 2

It becomes cooler and dimmer

Question 3

The Chandrasekhar limit is the

A)Greatest mass a white dwarf can have
B)Most massive main sequence star that can exist
C)Distance at which parallaxes can no longer be measured
D)Maximum brightness of a supernova

Answer 3

Greatest mass a white dwarf can have

Question 4

Why are there no white dwarf stars that can be seen with the unaided eye?

A)The nearest white dwarf is thousands of parsecs away
B)White dwarfs are very small in size
C)Even the hottest white dwarf is very cool
D)White dwarf stars are surrounded by thick dust shells

Question 5

Pulsars are

A)Spinning neutron stars with beamed radio emission
B)Black holes with accretion disks
C)Pulsating red giant stars with close companions
D)White dwarfs with periodic stellar winds
E)Binary systems with regular eclipses

Question 6

The Chandrasekhar limit is the largest mass that a white dwarf star can have.About how large is the Chandrasekhar limit?

A)1 solar mass
B)1.4 solar masses
C)2.5 solar masses
D)5.2 solar masses

Question 7

What fraction of the white dwarfs have masses greater than 8 times the mass of the Sun?

A)Nearly 100%
B)About 1 in a 100
C)About 1 in 10
D)None have masses that large

Question 8

A white dwarf star has the same mass as the Sun but a radius 1/100 that of the Sun.How does the surface gravity of the white dwarf compare with that of the Sun?

A)1/100 as large
B)The same
C)100 times as large
D)10,000 times as large

Question 9

Which of the following objects can rotate a thousand times per second without being torn apart?

A)White dwarf
B)Main sequence star
C)Red giant
D)Neutron star

Question 10

Which of the following is true of the central star of a planetary nebula?

A)It is about to become a white dwarf
B)It is about to produce a supernova outburst
C)It is a main sequence star
D)It is a proto-star

Question 11

Which of the following is true of neutron stars?

A)Many of them rotate faster than once per second
B)They are about as large as the Moon
C)They have small magnetic fields
D)They eventually become supernovas.

Question 12

What type of star is supported by the pressure produced by its degenerate electrons?

A)A white dwarf
B)A neutron star
C)A main sequence star
D)A pulsar

Question 13

Which of the following best describes the relationship between mass and radius for white dwarf stars?

A)Radius is independent of mass
B)More massive white dwarfs are larger
C)More massive white dwarfs are smaller
D)All white dwarfs have the same size

Question 14

Which of the following is true of a massive neutron star compared to one of smaller mass?

A)It is larger and lower in density
B)It is larger and higher in density
C)It is smaller and higher in density
D)It is smaller and lower in density

Question 15

A white dwarf star such as Sirius-B balances the inward gravitational force by

A)Radiation pressure
B)Degenerate electron gas pressure
C)Degenerate neutron gas pressure
D)Gas pressure from heat derived from fusion
E)Energy from recurrent novae

Question 16

Which of the following is true for white dwarf stars?

A)They have small radii and large densities
B)They have large radii and small densities
C)They have high luminosities and large radii
D)They have small masses and high luminosities

Question 17

The approximate size of a white dwarf is

A)10 km
B)The size of the Earth
C)The size of the Sun
D)Between 1.4 and 2.5 solar radii

Question 18

A neutron star has a radius of about

A)0.1km
B)10 km
C)1000 km
D)100,000 km

Question 19

The object at the center of the Crab Nebula is

A)A massive O star
B)A neutron star
C)A 10 solar mass black hole.
D)An X-ray binary
E)A white dwarf

Question 20

What kind of pressure supports a white dwarf star?

A)Degenerate neutron pressure
B)Radiation pressure
C)Normal gas pressure
D)Degenerate electron pressure

Question 21

What can escape from within the Schwarzschild radius of a black hole?

A)Nothing
B)Photons
C)Neutrinos
D)Antiparticles

Question 22

What happens to the escape velocity of an object when it collapses to a size equal to its Schwarzschild radius?

A)It goes to zero
B)It becomes infinite
C)It becomes negative
D)It becomes equal to the speed of light

Question 23

As a star collapses to produce a black hole,the photons that escape from it

A)Move faster than the speed of light
B)Are redshifted
C)Turn into neutrinos
D)Produce a white hole

Question 24

Suppose an astronaut travels close to a black hole's event horizon (but is smart enough not to enter!).If he remains 1 day by his clocks,when he returns to base,he will be

A)1 day older
B)More than 1 day older
C)Less than 1 day older
D)1 day younger

Question 25

The Crab Nebula is powered by

A)Radioactive decay
B)Release of gravitational potential energy
C)Rotational kinetic energy of the Crab Nebula pulsar
D)Nuclear reactions in the center of the nebula

Question 26

A pulsar spins rapidly because it

A)Conserved angular momentum when it shrank
B)Has been struck a glancing blow by another star
C)Has formed from a very rapidly rotating gas cloud
D)Has been accelerated by explosions on its surface

Question 27

The size of a black hole is entirely determined by which of the following?

A)Mass
B)Chemical composition
C)Age
D)Rate of accretion of new material

Question 28

If we could see the last few seconds of the collapse of a star to form a black hole,we would see the star grow steadily redder.Why?

A)The star moves away from us at an increasing speed
B)The star grows steadily cooler
C)The star's gravitational redshift increases
D)The star becomes obscured by more and more interstellar dust

Question 29

Pulsars were first discovered

A)While studying radio scintillations in the solar wind
B)While studying rapidly variable stars
C)In globular clusters
D)In a search for 21 cm radiation from other galaxies.

Question 30

Which of the following is an essential part of Einstein's explanation of gravity?

A)Matter causes curvature of space
B)The gravity of a moving object varies with time
C)Gravitational forces exist only over a limited distance
D)Anti-matter has negative gravity

Question 31

The Schwarzschild radius describes the size of a(n)

A)Black hole
B)Neutron star
C)Accretion disk
D)White dwarf

Question 32

According to general relativity,what effect does matter have on space?

A)Matter causes space to exert gravitational forces
B)Matter curves space
C)Matter causes space to expand
D)Matter causes space to contract

Question 33

A rotating neutron star is called a

A)Pulsar
B)White dwarf
C)Black hole
D)Quasar

Question 34

A typical pulsar rotates once per

A)Year
B)Day
C)Hour
D)Second

Question 35

Electrons moving in a magnetic field produce radiation by the process of

A)Synchrotron radiation
B)Black body emission
C)Bright line emission
D)Electron scattering

Question 36

How do we know that pulsars aren't rotating white dwarfs?

A)A white dwarf would break up if it rotated as fast as a pulsar
B)There is only one rate at which white dwarfs can rotate
C)White dwarf stars can't rotate
D)There are not enough white dwarfs to account for the number of known pulsars

Question 37

Suppose you were inside the Schwarzschild radius of a black hole.If you were to shine a blue flashlight to a companion exterior to the black hole,he/she would see

A)Red light
B)Blue light
C)Violet light
D)No light (can't escape)
E)White light

Question 38

Which of the following cannot be determined for the material inside a black hole?

A)Mass
B)Electric charge
C)Chemical composition
D)Angular momentum

Question 39

What kind of telescope was used to detect the first known neutron star?

A)A radio telescope
B)An optical telescope
C)An orbiting ultraviolet telescope
D)An infrared telescope

Question 40

What happens to the light from a star that has contracted within its event horizon?

A)It cannot escape from the region around the star
B)It begins to travel faster than the speed of light
C)It has a strong blue shift
D)There is no longer any relationship between wavelength and energy

Question 41

What produces the energy that is released in a Type II supernova explosion (of which SN 1987A was an example)?

A)Gravitational collapse
B)Very rapid consumption of hydrogen
C)The collision between two stars
D)The impact of an antimatter asteroid on a star

Question 42

If the unseen component of a binary star has a mass greater than about 3 solar masses,theory tells that it must be what kind of object?

A)A black hole.
B)A neutron star.
C)A red giant.
D)A white dwarf.

Question 43

The bright star seen by Chinese astronomers during daylight in the year 1054 AD was (not counting the Sun!)

A)The first appearance of Comet Halley
B)The Crab supernova
C)The formation of a massive black hole in the galactic center
D)Alpha Centauri reaching the main sequence
E)A helium flash on Sirius

Question 44

The radius of the black hole that could be produced from the contraction of a star like the Sun would be about

A)The same as the radius of the Earth
B)3 km
C)1 AU
D)21 cm

Question 45

How do we know that gamma ray bursts occur at very great distances?

A)They occur in highly redshifted galaxies
B)They are all too faint to be nearby
C)They are confined to the plane of the Milky Way
D)They show no parallax

Question 46

If the Sun were replaced by a black hole having a mass of 1 solar mass,what would happen to the Earth's orbit?

A)The Earth would spiral inward
B)The Earth would jump to a smaller orbit
C)The size of the Earth's orbit would increase rapidly
D)The Earth's orbit would remain the same

Question 47

Suppose a star collapses and produces a black hole.The size of the event horizon of the black hole is determined entirely by the star's

A)Mass and chemical composition
B)Age
C)Luminosity and temperature
D)Mass alone

Question 48

Approximately how massive must a black hole be in order to be as large as the Earth (6000 km in radius)?

A)A few hundredths of a solar mass
B)A few solar masses
C)A few tens of solar masses
D)A few thousand solar masses

Question 49

The Schwarzschild radius of a 10 solar mass black hole is about 30 km.How large is the Schwarzschild radius of a 5 solar mass black hole?

A)7.5 km
B)15 km
C)60 km
D)120 km

Question 50

The best observational evidence for the existence of black holes is

A)Pulsar emission
B)Massive,mass-transfer X-ray binaries
C)Evolved red giants with masses in excess of 3 solar masses
D)Supernova explosions
E)Planetary nebulae

Question 51

The term "event horizon" refers to which of the following?

A)The depth to which we can see into the Sun
B)The surface of a black hole
C)The greatest distance to which we can see with current telescopes
D)The obscuration of starlight by interstellar dust

Question 52

Which is not an end point of a star's evolutionary life?

A)Black hole.
B)Neutron star.
C)White dwarf.
D)Red giant.