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1P02 ASTRO - INTRO II > Part 1 > Flashcards

Flashcards in Part 1 Deck (178):
1

Where do Stars Form?

Stars form in low-density gas and dust between starts. The interstellar medium.

2

How do Stars Form?

The combined gravitational attraction of atoms in a cloud of gas will shrink the atoms, pulling them toward the centre. Thermal energy resists collapse, however, a stable cloud that collides with a shockwave can be compressed and disrupted into fragments. Some of these fragments can be dense enough to collapse under their own gravity and form stars.

3

Describe some of the main properties of interstellar clouds of gas and dust. What is their role in star formation?

Clouds of gas and dust form the interstellar medium in which stars can form. It is made up of roughly: 75% hydrogen, 25% helium, traces of carbon, nitrogen, oxygen, calcium, sodium, and heavier atoms. Roughly 1% is made up of interstellar dust - microscopic grains of mostly carbon and silicates.

4

What are protostars? How do they form?

A collapsing cloud of gas and dust destined to become a star. Once triggered to collapse, gravity draws atoms toward the centre, atoms pick up speed, becoming denser, the atoms collide more often, temperature goes up. This forms a dense core and a warm protostar develops.

5

What is the role of a protostar in stellar formation?

Protostars become main sequence stars.

6

How do the properties of protostars differ from those of interstellar clouds of gas and dust?

Protostars have been triggered to collapse and are drawing inward.

7

How do the properties of protostars differ from those of stars? How do protostars evolve.

Protostars are not yet stars. They are in the process of condensing. Once internal temperatures become hot enough, the gas will become ionized. Once internal temps are hot enough nuclear reactions begin to take place that will generate enough energy to replace energy leaving the star. Contraction then halts and the protostar becomes a main sequence star. Mass determines how long it takes for the protostar to evolve into a star.

8

Why are stars that have extremely high masses rare?

Star with high mass spend their fuel rapidly and have short lives. Stars with lower mass conserve their fuel and have longer lives.

9

What is a nebula?

A relatively dense cloud of interstellar gas and dust

10

What are the three main types of nebulae?

Reflection Nebula, Dark Nebula, Emission Nebula

11

Why do reflection nebulae appear blue?

For the same reason the sky looks blue. The dusty nebula scatters short wavelengths more easily than long wavelengths. The blue colour shows that the dust particles must be very small to scatter blue photons.

12

Why are dark nebulae called dark? How can they be observed?

They are dense clouds of gas and dust that obstruct the view of more distant stars. They can be observed in the infra-red.

13

What is the appearance of an emission nebula? What is their appearance, and what explains their appearance?

Emission nebulas appear pink. This occurs because a hot star excites the gas near it to produce an emission spectrum of ultraviolet.

14

What are the basin properties of giant molecular clouds?

15 to 600 ly in diameter. Dense clouds of dust

15

How do clumps form in giant molecular clouds?

Dust blocks the starlight. Which keeps it cool enough for Hydrogen atoms to bind into hydrogen molecules. Shockwaves from explosions passes through the clouds and triggers creation of the clumps. Some dense clumps begin to collapse under their own weight. 

16

How do clumps in giant molecular clouds evolve? What are the conditions for which this kind of evolution takes place?

Dust blocks the starlight. Which keeps it cool enough for Hydrogen atoms to bind into hydrogen molecules. Shockwaves from explosions passes through the clouds and triggers creation of the clumps. Some dense clumps begin to collapse under their own weight. They heat up as gravitational energy is converted to thermal energy. Becoming a protostar. If the clump has enough mass to reach 10mil degree kelvin within the protostar a reaction takes place. Becoming a main sequence star.

17

How long does it take for a protostar to become a main-sequence star?

Depending on the mass of the clump. 15 mass only takes 100,000 years with contraction period of 160 million years

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18

What is the "birth line?" What is its signifgance?

A line that stars cross in their birth were they become hot enough to see on infra-red.

19

How massive are low-mas stars, medium-mass stars, and high-mass stars? In which category is the sun?

.08M < M < .5M (low mass) - low luminosity - low temperature - long life

.5M < M < 8M (medium mass) - our sun is in this category. - meduim

8M < M (high mass) - High luminosity - high heat - short life

20

Which property mainly determines the evolution of a main-sequence star?

It's mass

21

What are brown dwarfs? What are some of their properties?

Protostars that did not have enough mass to enter the main-sequence. Properties are similar to that of stars.

22

What is the proton-proton chain? Describe some of its properties. What is its effect in stars?

A series of three nuclear reactions that builds a helium atom by adding together protons; the main energy source of the sun.  Some properties are deuterium ( an isotope of hydrogen in which the nucleus contains a proton and a neutron. Positron (The antimatter equivalent of an electron; same as an electron but with a positive charge as opposed to negative. Neutrino (A neutral, nearly massless atomic particle that travels at or near the speed of light.

It creates stability within stars in luminosity and energy release.

23

What are red dwarfs? What are their properties?

A low mass star. That burns red in colour. They are hard to see because they emit less energy. Most stars in the universe are likely red dwarfs that cannot be seen.

.08M < M < .5M (low mass) - low luminosity - low temperature.

24

What is the CNO cycle? Describe some of its properties. What is its effect in stars? In which kind of stars is it important?

A series of nuclear reactions that use carbon as a catalyst to combine four hydrogen nuclei to make one helium nuclei to make one helium nucleus plus energy; effective in stars more massive than the sun.

25

What is hydrostatic equilibrium? Which kinds of star are in hydrostatic equilibrium?

A basic law of stellar structure. The weight on each layer must be balanced by the pressure in that layer. The pressure and temperature increase with depth. Main-sequence stars are in hydrostatic equilibrium.

26

Explain how the luminosity of a main-sequence star changes over time. What is the reason for this change?

Main-sequence stars become more luminous over time. To maintain the pressure to support the top layers that decrease in temperature over time the star needs to expend more energy over time. Increasing luminosity.

27

Explain the life history of a medium-mass star. Explain each stage in detail, and explain the reasons for each important event in the later stages of evolution of a medium-mass star.

1- Protostar forms

2 - period of instability with bi-polar flows

3 - Main sequence stage

4 - first red giant stage - Begins when all hydrogen is used up - star swells up.

5 - eventually helium gets hot enough and fuses with carbon - short lived yellow giant stage

6- second red giant phase

7 - energy is pushed out forming a planetary nebula with a dead core that is very hot and dense.

8 - This remaining core is a white dwarf.

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28

What is the triple-alpha process? What is its effect in a star?

A set of nuclear fusion reactions by which 3 helium 4 nuclei are transformed into carbon. The first red giant stage into the yellow giant phase.

29

What is the helium flash? When does it occur, and what is the star like when it occurs?

It occurs with the onset of helium fusion within a star. This occurs and the star enters the yellow giant phase.

30

What is a planetary nebula?

Spherical shell of stars material pushed out by the thermal and radiation pressure during the final red giant phase

31

How are planetary nebula formed?

Thermal pressure and radiation pressure of the central object (dying star) push of top layers of star during the final red giant phase, to form a shell of gas and material around a dead star

32

How massive must be a star be for a planetary nebula to be formed after its death?

Medium mass

33

What accounts for the appearance of a planetary nebula?

We see them as a ring but they are spheres of material having been pushed out. The aura is brighter than the star.

34

What happens to the central star during the process of the formation of a planetary nebula?

It becomes dead, a white dwarf

35

Why do planetary nebula appear somewhat ring shaped even though they may be closed to spherical shells or have other unusual shapes?

Because the outer aura is brighter than the star.

36

Why are planetary nebula called "planetary" when they have nothing to do with planets?

Because they take on the colours of planets.

37

What are some of the properties of white dwarfs and how do they compare to main-sequence stars?

Extremely dense. Been compressed. 100kg per cm cubed, million times more dense than water. Extremely heavy.

38

What is the composition of a typical white dwarf?

Very hot, low luminosity. It has exhausted its helium and hydrogen, leaving only carbon and oxygen.

39

Ordinary stars use gas pressure, fuelled by fusion reactions, to balance gravity. White dwarfs do not sustain fusion reactions, so how do they maintain stability against gravitational collapse?

Supported against collapse by electron degeneracy pressure.

40

How does the position of a medium-mass star on it H-R diagram change as the star evolves from a protostar through its main-sequence phase and the later stages of its life, culminating in a white dwarf?

As a star grows older it moves down the HR diagram.

41

What are some of the unusual properties of degenerate matter, such as found in white dwarf?

The pressure does not depend on temperature, but only on density.

Larger mass has smaller radius/size

42

How does the radius of a white dwarf depend on its mass?

The higher the mass the smaller the radius. The lower the mass the higher the radius

43

What is the concept of the Chandrasekhar mass limit? What is the approximate value of the Chandrasekhar mass limit? What is the signifgance of this value of observations of white dwarfs?

- The maximum mass of a degenerate body.

- Max value is 1.4mass

- The smaller the mass the higher the radius. The higher the mass the smaller the radius. Most white dwarfs .5M to .7M

44

How do White dwarfs produce light?

White dwarf carbon nuclei do not obey pali principle. The number of nuclei is not limited. Some carbon still emits light. Eventually all nuclei will drop to the lowest energy level and star will become a black dwarf. Very ling time.

45

How do planetary nebula produce light?

White dwarfs have a high surface temp and emit alot of UV photons, these excite the electrons into higher energy states. As they drop back to their lower energy state photons are emitted which emit fluorescence. Emitting light.

46

What is a type Ia supernova? What are the typical ways in which type Ia supernova occur?

Strong gravity near a dense white dwarf attracts some of the material from companion star and the mass of the white dwarf increases. It compresses and heats up. Once it gets close to the Chandrasekhar limit there is runaway fusion reactions  - the entire system is disrupted and a massive explosion occurs. Type 1a supernova

47

Which chemical elements are produced in a type Ia supernova explosions? How are they produced? How are they dispersed into the interstellar medium?

Through high temps generated fusion into heavier elements such as - Silicon, unburned carbon and oxygen, iron and heavier elements become part of the interstellar cloud of gas enriched with elements that are crucial to life.

48

What is the remnant left by a type Ia supernova explosion?

The white dwarf is entirely destroyed with no remnant

49

What is a distinctive feature of the spectrum of type Ia supernova?

No hydrogen spectrum lines - all hydrogen was used up in the explosion

50

How are type Ia supernova used to help determine the distance of distant galaxies?

Very bright, easy to see over long distances. Because we know mass from chandra, we can determine luminosity - from this distance can be deduced

51

How does the evolution of a high-mass star differ from the evolution of lower-mass stars?

- All stages in the evolution happen faster. Higher mass = equal shorter life.

- The mass is so high that helium is fused into carbon - it goes directly to yellow giant phase.

52

What is nucleosynthesis? How, when, and why does it occur in a very massive star?

Progressive heavier and heavier nuclei are formed.

53

What result does nucleosynthesis have on the composition of the interstellar medium?

Many of the elements in the interstellar medium are formed through nucleosynthesis.

54

What is core collapse? When and why does it occur? What are the effects of core collapse? What is the resulting remnant?

The mass of the iron core increases as more and more iron is produced in the si-fusing shell. Eventually the chandrasekhar limit is reached for degenerate iron and the core collapses. The core shrinks into a neutron star (mostly of neutrons) or if the mass of the core is large enough it collapses into a black hole.

55

How does the position of a high-mass star on its H-R diagram change as the star evolves through its life?

It will burn hotter and hotter (higher and higher), then move down the diagram as its fuel is expended.

56

What is nuclear binding energy? What is its role in the late stages of stellar evolution for high-mass stars?

Nuclear binding energy is the minimum energy that would be required to disassemble the nucleus of an atom into its component parts.

57

What is the remnant left behind by a high-mass star? How does it form?

There is a gas ejected which slams into gas surrounding the star, creating a glow: the supernova remnant. Inside the remnant will be a neutron star.

58

Explain how a type-II supernova is created.

The core collapse of a massive star.

59

How does the spectrum of a type-II supernova differ from that of a type-Ia supernova?

The spectrum of a type II contains hydrogen spectral lines

60

What are some of the properties of a neutron star? What is the mass limit for a neutron star? What happens if the mass limit is exceeded?

The axis are not pointing in the same direction(spin axis and magnetic axis). As neutrons are released they spiral and create magnetic field. This creates highly directional electromagnetic radiation.

61

What is some of the observational evidence for the existence of neutron stars? How were neutron stars first discovered?

Visual and radio wave paper. By Jocelyn Bell in the 1960's by observing paper printouts and finding a pattern.

62

What is a pulsar?

A fast moving neutron star

63

Why do neutron stars spin so much more rapidly than stars? Why does the rotation rate of a neutron star gradually decrease?

Angular momentum. A mass condenses(shrinks) spin increases. It gradually decreases as energy is lost via rotational energy.

64

What is the internal structure of a neutron star, as inferred from observations?

The mass of a collapsed core, very dense, different kinds of neutrons at different layers.

65

What is a black hole? How do black holes form?

Black holes occur when the collapsing core of a supernova greater than 3 solar masses contracts to such a small size that no radiation can escape. A singularity in space-time

66

What is the concept of escape velocity? How can you calculate the escape velocity from the surface of an astronomical object of mass M and radius R? How does the escape

velocity change if an object of mass M contracts so that its radius decreases?

Escape velocity is the speed that an object needs to be traveling to break free of a planet or moon's gravity well and leave it without further propulsion.

 

Escape velocity = GM (Gravitational consent) / R (result obtained with Newtonian gravity

 

For given mass (M) as the radius (R) is reduced Vel increases and could become greater than the speed of light.

67

Why is a black hole called black?

Escape velocity is so high that not even light can escape

68

What is a singularity?

 

An object of zero radius and infinite density

69

What is an event horizon?

The boundary of a black hole from which no radiation may escape. No event that occurs within the event horizon is visible to a distant observer.

70

What is the Schwarzschild radius of a black hole?

It is a distance from the body within which the escape velocity is greater than the speed of light.

71

What is some observational evidence for black holes?

Look for a binary system with a normal star and a invisible companion with a mass of at least 3M with a strong source of x-rays

72

What is the basic idea of Einstein's theory of general relativity? How is this perspective different from Newton's theory of gravity?

That massive objects cause a distortion in space time which is felt as gravity.

73

 

What are some of the important predictions of Einstein's theory of general relativity?

Gravitational Redshift - as a photon escapes the gravitational pull by mass it loses energy and the wavelength of light increases

74

What is some observational evidence that supports Einstein's theory of general relativity?

The stronger the forces of gravity the slower clocks run, Redshift

75

Why is taking relativity into account essential for the accuracy of the global positioning system (GPS)?

Relativistic effects must be taken into account when designed GPS satellites to have their clocks run 7ms per day slower because they would slowly get too fast

76

What is the origin of the term Milky Way?

The Romans named it via lactea precisely because it looks like a milky patch of sky above the Earth at night. But, the Romans weren't the first to name the galaxy. The Romans got the name from the Greeks, who called it galaxias kyklos, which translates into “milky circle.”

77

Who first observed that the milky way is made up of an enormous number if stars? When did this occur, and what was the signifgance of the observation?

Galileo. 1609. It explained the milky band. And opened the door to determining out place in the galaxy. That there are many stars

78

What is a globular cluster? How are they used to determine distances in the Milky way?  Who first used globular clusters to determine distances in the Milky Way?

Widely scattered star clusters more common toward the constellations Sagittarius and Scorpius.

The concentration of globular clusters was assumed by Harlow Shapley to be controlled by the combined gravitational field of all the stars in the galaxy

He measured the distances to as many globular clusters as possible

79

What is the Cepheid Variable? What is the period-luminosity relationship for Cepheid variables, and who discovered it? How are Cepheid variables used to determine distances in the Milky Way?

They are pulsating yellow giant star. Henrietta Levitt.

 

Shipley found the true luminosity of Cepheid variables and used this to measure their distance from us.

80

How do we know our approximate location within the Milky Way? How was this determined?

Shapley argued that globular clusters must be near the galactic centre. Basing his measurement of average distances from Cepheid variables he approximated our location in the milky way.

81

What is the approximate size and shape of the milky way galaxy? How do we know this?

A disc with spiral arms. Apx 100,000 light years across. Our sun to centre is approx 30,000 light years.

 

Based of observations building from Shapley

82

Describe the content of the Milky Way: star, star clusters (associations, open clusters, globular clusters), gas, dust: other objects (planets, asteroids, comets, etc) will be discussed later.

Stars, star clusters, gas and dust.

The clusters are associations: cluster of 10-100, young and hot (o and B class) luminous stars

Or Open clusters: clusters of 100-1000 stars. Also hot and luminous

83

Describe the structure of the Milky Way: the disk (which includes the spiral arms), the central bulge, and the halo. How do we know this?

The milky way has a centre bulge surrounded by a disk with spiral arms. From observation of other spiral galaxies and the location of blue luminous stars.

84

How do population I stars differ from population II stars is composition? How do they differ in location in the galaxy?

Population I (in disk ) stars are composed of 2-3% metal. Population II ( in halo and bulge) stars are .1% metal.

85

How do disk stars move?

pic

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86

How do bulge stars move?

 

How do halo stars move?

How do bulge stars move?

 

The motions of bulge stars are similar to those in the halo

 

How do halo stars move?

 

Move along Highly elliptical orbits randomly oriented and with no overall direction of motion )like the bees in a beehive

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87

How do we know the approximate mass of the milky way?

From the rotation curves in the galaxy and how mass interacts.

88

What is the concept of dark matter? What is the evidence and reasoning used to infer the existence of dark matter?

It was observed that things move too fast if only the matter that is visible was accounted for. So the observed gravitational energy is insufficient for how galactic objects interact. Therefore some "dark matter" unseen, must be at play

89

What are some candidates for dark matter?

MACHO - Massive, Astrophysical, compact halo objects: Black holes,  neutron stars, old brown dwarfs, white dwarfs. All detected though gravitational microlensing

 

WIMP - Weakly Interacting Massive Particles: assumed to be massive particles that interact with each other. Never observed.

90

What are the spiral arms of the milky way like? What do they contain? How do they move? What is their role is star formation?

They are the waves of compression of the material in the disk and they move around more slowly than the individual stars.

 

They contain clouds of gas and dust.

 

As new material enters the arm it gets compressed and can start star formation.

 

Hot stars may spend their life in the arm. Lower mass stars will move slower than the arm.

91

What is the centre of the milky like?

Dense of clouds of dust and luminosity

92

The Centre of the Milky way is obscured from us by enormous clouds of gas and dust, which block the visible light from the galactic centre. How then can we observe the galactic centre?

We observe through radio and x-ray wavelengths.

93

What is the evidence for a massive central object at the galactic centre? What is this object believed to be?

Believed to be a supermassive black hole. Using third Kepler's law to analyze orbital data of orbits of objects around the centre show the approximate size of the central object to be 4 million solar mass. Something that big can only be a supermassive black hole as observed in the centre of other galaxies.

94

protostar

95

Main-sequence stars are in hydrostatic equilibrium, which means the inward gravitational forces are balanced by outward forces due to
 

gas pressure.

96

In the Sun, the convective zone is
 

near the surface of the Sun.

97

The processes that produce radiant energy in the Sun can be summarized as ____ hydrogen nuclei combine to produce a helium nucleus and energy is released.
 

(a) 2 (b) 3 (c) * 4 (d) 5 (e) [None of the above.]

98

As a contracting protostar heats up, if the core temperature reaches  _____ then fusion of hydrogen into helium begins and the protostar becomes a main-sequence star

(a) 10 thousand degrees K (b) * 10 million degrees K (c) 10 billion degrees K (d) 10 trillion degrees K
 

99

High temperatures and pressures are required to produce nuclear reactions because this helps

 to overcome the electrical repulsion between atomic nuclei.

100

As a main-sequence star evolves, steadily converting hydrogen to helium in its core, the core of the star gradually

becomes hotter and contracts.

101

As a main-sequence star evolves, steadily converting hydrogen to helium in its core, the outer layers of the star gradually

 become cooler and expand

102

Heat flows from a star’s core to its surface because

the star’s core is hotter than its surface

103

 For a low-mass main-sequence star, hydrogen is fused into helium mainly by
 

the proton-proton chain.

104

 For a high-mass main-sequence star, hydrogen is fused into helium mainly by
 

 the CNO cycle

105

 Main-sequence stars with masses less than 0.4 solar masses are
 

 red dwarfs

106

An important way that astronomers measure distances to other galaxies is using
 

Cepheid variable stars.

107

The mass of Star A is much greater than the mass of Star B, and they are both mainsequence stars. The rate at which Star A consumes its hydrogen fuel is _____the rate at which Star B consumes its hydrogen fuel.
 

greater than

108

 Small, dark clouds called Bok globules are found in and near
 

star-forming regions of space

109

The formation of “heavy elements” (nucleosynthesis) occurs primarily during
 

the core collapse of a high-mass star

110

The distances to the most distant galaxies are measured using
 

Type Ia supernovae

111

 Red dwarfs have been observed to finish consuming all of their available hydrogen fuel
 

[This has never been observed.]
 

112

Degenerate matter is found
 

in the core of a white dwarf

113

An accretion disk is formed from
 

gas flowing from a companion star towards a white dwarf

114

The surface temperature of a white dwarf is typicall

greater than the Sun’s surface temperature

115

The density of a white dwarf is typically

greater than the Sun’s density.

116

In a white dwarf, equilibrium is maintained by a balance of
 

electron degeneracy pressure and gravity.

117

 If the mass of a neutron star were to suddenly increase to greater than about_____ , then it would collapse into a black hole.
 

3 solar masses

118

When a type Ia supernova explodes, it leaves behind
 

no central remnan

119

When a type II supernova explodes, it leaves behind
 

(a) a white dwarf as a central remnant. (b) a neutron star as a central remnant. (c) a black hole as a central remnant. (d) no central remnant. (e) * [Either (b) or (c) could occur.]

120

Neutron stars typically
 

 have smaller diameters and are more dense than white dwarfs

121

 Type Ia supernovae
 

do not have hydrogen spectral lines in their spectra

122

 Type II supernovae
 

 have hydrogen spectral lines in their spectra

123

Binary pulsars emit ____that can be used to test_____

 gravitational waves / Einstein’s theory of general relativity

124

In an X-ray binary star, the object emitting the X-rays is
 

a neutron star

125

As the 20th century began, astronomers generally believed that the Sun was located near the centre of a wheel-shaped star system that they estimated had a diameter of
 

about 15,000 light-years

126

 The first reasonably good approximation for the size of the Milky Way was determined by
 

Harlow Shapley.

127

The first reasonably good approximation for the size of the Milky Way was determined by measuring the distances to

globular star clusters.

128

Early 20th-century astronomers observed that the Milky Way’s globular star clusters appeared to be centred at a point many thousands of light-years away in the direction of the constellation
 

 Sagittarius

129

One way astronomers deduce the mass of the Milky Way is to study

the orbital motions of stars in the galaxy.

130

 The number of stars in the Milky Way is approximately
 

100 billion.

131

Density wave theory is currently the most popular accepted explanation for the formation and evolution of the Milky Way’s

spiral arms.

132

 Population I stars are typically found in the Milky Way’s
 

spiral arms, have approximately circular orbits, and have relatively high heavyelement content.

133

 Population II stars are typically found in the Milky Way’s

 halo and bulge, have eccentric orbits, and have relatively low heavy-element content

134

The Milky Way rotates in such a way that
 

the central parts of the galaxy rotate faster than the outer parts

135

The Milky Way’s disk contains most of its
 

younger stars.

136

According to current theories of the Milky Way’s evolution, the shape of the Milky way is predicted to become ____as it evolves

flatter

137

 There is so much interstellar dust in the Milky Way’s disk that
 

 the nucleus of the Milky Way can’t be observed at visual wavelengths

138

Main-sequence stars are in hydrostatic equilibrium, which means a balance between a star’s

 inward gravitational forces and outward forces due to core pressure

139

For a star in hydrostatic equilibrium, energy is transported in the star primarily by
 

convection and radiation.

140

In the Sun, the convective zone is
 

near the surface of the Sun.

141

High temperatures and pressures are required to produce nuclear reactions because this helps

 to overcome the electrical repulsion between atomic nuclei

142

 A vast number of neutrinos is produced in the Sun’s
 

 core

143

As a main-sequence star evolves, steadily converting hydrogen to helium in its core, the core of the star gradually
 

becomes hotter and contracts.

144

As a main-sequence star evolves, steadily converting hydrogen to helium in its core, the outer layers of the star gradually
 

become cooler and expand

145

 A mass of about 1.4 solar masses is the maximum mass for a
 

white dwarf star

146

 Main-sequence stars produce radiant energy primarily by
 

nuclear fusion.

147

The Sun began its life as a

cold, dark cloud of gas

148

During the very early stages in the formation of a protostar, clumps of gas are
 

compressed and heated.

149

 T Tauri stars are examples of
 

protostars.

150

The proton-proton chain is the primary means for fusing hydrogen into helium in
 

low-mass main-sequence stars

151

Main-sequence stars with masses less than 0.4 solar masses are
 

red dwarfs.

152

Period-luminosity relationships for stars such as Cepheid variables give astronomers a powerful tool for measuring
 

 distances to other galaxies

153

 The CNO cycle is the primary means for fusing hydrogen into helium in
 

high-mass main-sequence stars

154

The formation of “heavy elements” (nucleosynthesis) occurs primarily during
 

the collapse of the core of a high-mass star

155

An accretion disk is formed from
 

 gas flowing from a companion star towards a white dwarf.

156

The distances to the most distant galaxies are found using
 

 Type Ia supernovae

157

Most of the energy produced in Type II supernovae explosions is carried away by
 

 neutrinos

158

The surface temperature of a white dwarf is typically
 

 greater than the Sun’s surface temperature

159

In a white dwarf, equilibrium is maintained by a balance of
 

electron degeneracy pressure and gravity.
 

160

If the mass of a neutron star were to suddenly increase to greater than about 3 solar masses, then it would
 

 collapse into a black hole

161

The electromagnetic radiation emitted by a pulsar is due to charged particles spiralling about
 

 magnetic field lines

162

The diameter of a white dwarf is typically about
 

the diameter of the Earth

163

When a type Ia supernova explodes, it leaves behind
 

no central remnant

164

The Schwarzschild radius is
 

 the radius of the region around a black hole within which not even light can escape

165

The diameter of a neutron star is typically about
 

(a) half the diameter of the Sun. (b) the diameter of Jupiter. (c) the diameter of the Earth. (d) the diameter of the Moon. (e) * [None of the above.]
 

166

 The Crab Nebula is a

supernova remnant

167

We detect regularly-spaced pulses of electromagnetic radiation from pulsars due to their
 

 nearly constant rotation rates

168

A binary system that includes _____that has a mass of at least 3 solar masses provides strong evidence for the existence of a black hole.
 

an ordinary star and an invisible X-ray emitter
 

169

That the Milky Way is made up of an enormous number of individual stars was confirmed by Galileo in 1609, but was first suggested by
 

Anaxagoras and Democritus in 400 BCE

170

The period-luminosity relationship for Cepheid variable stars was first observed by
 

Henrietta Swan Leavitt in 1912.

171

The first reasonably good approximation for the size of the Milky Way was determined by
 

Harlow Shapley

172

The age of the Milky Way is approximately
 

 9 billion to 13 billion years old.

173

 One way astronomers deduce that the Milky Way has a disk-like shape is that they observe
 

the great majority of stars in a band that encircles us

174

 The centre of the Milky Way, from the Earth’s reference point, is in the direction of the constellation
 

Sagittarius.
 

175

 The number of stars in the Milky Way is approximately
 

 100 billion

176

Most of the Milky Way’s younger stars are found in its
 

 disk

177

 Most of the Milky Way’s stars that have a relatively high concentration of heavy elements are found in its
 

disk.

178

 Most of the Milky Way’s stars that have a relatively low concentration of heavy elements are found in its
 

halo and bulge