ch.15

Question 1

What are hot, compact stars whose mass is comparable to the Sun’s and size to the Earth’s?

Answer 1

White dwarfs

Question 2

What is the approximate surface temperature of white dwarfs?

Answer 2

25,000 K

Question 3

What generates the light of a white dwarf?

Answer 3

Residual heat (no fusion)

Question 4

What elements mainly compose a white dwarf?

Answer 4

Carbon and oxygen with a thin hydrogen/helium surface layer

Question 5

What happens to a white dwarf over billions of years?

Answer 5

It cools until it becomes a black dwarf

Question 6

What is a neutron star?

Answer 6

An end state of a supernova explosion of a massive star (> 8 M ⊙)

Question 7

What is the typical radius of a neutron star?

Answer 7

About 10 km

Question 8

What is the mass range of a neutron star?

Answer 8

Between 1 M ⊙ and a maximum of about 3 M ⊙

Question 9

Who discovered pulsars and when?

Answer 9

Jocelyn Bell in 1967

Question 10

What is the period-density relation for ordinary pulsating variables?

Answer 10

Period is inversely proportional to the square root of its density

Question 11

What key characteristic explains pulsars?

Answer 11

A rotating neutron star

Question 12

What principle explains the rapid rotation of neutron stars?

Answer 12

Conservation of angular momentum

Question 13

What generates the pulsar’s emissions?

Answer 13

Powerful magnetic field beaming radiation energy

Question 14

What causes the pulsation of a pulsar as observed from Earth?

Answer 14

Radio beams sweeping across the Earth

Question 15

What phenomenon do compact objects generate when orbiting each other?

Answer 15

Gravitational waves

Question 16

When were gravitational waves detected?

Answer 16

2016

Question 17

What happens to a binary system due to gravitational waves?

Answer 17

It loses energy, making the stars move closer together

Question 18

What results from the collapse of stars greater than 10 M ⊙?

Answer 18

A black hole

Question 19

What is the escape velocity of a black hole?

Answer 19

Exceeds the speed of light

Question 20

What does Einstein’s general theory of relativity relate to black holes?

Answer 20

Gravity is related to the curvature of space

Question 21

What is the event horizon of a black hole?

Answer 21

The spherical surface encompassing the black hole

Question 22

How do astronomers typically observe black holes?

Answer 22

Indirectly, by looking for effects on nearby objects

Question 23

What forms around a black hole in a close binary system?

Answer 23

An accretion disk

Question 24

What is the significance of the periodic disappearance of x-ray signals?

Answer 24

Indicates the presence of a black hole

Question 25

What is the Chandrasekhar limit?

Answer 25

The maximum mass a white dwarf can have

Question 26

What happens when a white dwarf exceeds the Chandrasekhar limit?

Answer 26

It may undergo a Type Ia supernova explosion

Question 27

What type of supernova occurs when a single high mass star explodes?

Answer 27

Type II supernova

Question 28

What recurring event occurs in a binary system with a white dwarf?

Answer 28

Nova

Question 29

What is the typical size of a neutron star?

Answer 29

10 km or less

Question 30

What happens in a binary system with a neutron star?

Answer 30

X-ray bursts may occur

Question 31

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

Answer 31

Speed of light

Question 32

What type of radiation do black holes emit?

Answer 32

Hawking radiation

Question 33

What is the temperature of black holes estimated to be?

Answer 33

Less than 1 millionth of a degree

Question 34

What is the rotation rate of millisecond pulsars?

Answer 34

About 1000 times per second

Question 35

What do scientists initially think caused the pulsations of pulsars?

Answer 35

Variable stars

Question 36

What are the two important properties of young pulsars?

Answer 36

Extremely rapid rotation and a strong magnetic field

Question 37

The laws of presently known physics break down inside an event horizon. True or False?

Answer 37

True

Question 38

The surface temperature of a white dwarf is higher than the surface temperature of the Sun. True or False?

Answer 38

True

Question 39

White dwarfs with a larger radius have more mass than white dwarfs of smaller radius. True or False?

Answer 39

False

Question 40

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. True or False?

Answer 40

True

Question 41

White dwarfs have magnetic fields as much as 100 million times larger than the Earth's magnetic field. True or False?

Answer 41

True

Question 42

The interior of a white dwarf behaves like a degenerate gas. True or False?

Answer 42

True

Question 43

If the mass of a white dwarf increases, it shrinks and then explodes if the mass exceeds 1.4 solar masses. True or False?

Answer 43

True

Question 44

The fast rotation of neutron stars is a consequence of the law of conservation of angular momentum. True or False?

Answer 44

True

Question 45

Neutron stars must have a mass smaller than the Chandrasekhar limit. True or False?

Answer 45

False

Question 46

The spectral lines of white dwarf stars are redshifted due to high gravity. True or False?

Answer 46

True

Question 47

Nova explosions involve a binary system of a white dwarf and a companion star and can occur repeatedly. True or False?

Answer 47

True

Question 48

A type Ia supernova will most likely leave no remnant star. True or False?

Answer 48

True

Question 49

Pulsars are rotating neutron stars. True or False?

Answer 49

True

Question 50

The strong gravitational field of a white dwarf results in gravitational redshift. True or False?

Answer 50

True

Question 51

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

Answer 51

False

Question 52

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

Answer 52

True