life and death of stars Flashcards
1
Q
What is the visibility of stars on a clear, dark night?
A
A few thousand stars are visible to the naked eye
2
Q
How do stars form?
A
Stars are born from clouds of interstellar gas
3
Q
What is a star cluster?
A
A group of stars that formed together from the same interstellar cloud
4
Q
Why are star clusters useful to astronomers?
A
- All stars in a cluster lie at about the same distance from Earth
- All stars in a cluster formed at about the same time
5
Q
What are the two main types of star clusters?
A
- Open clusters
- Globular clusters
6
Q
What are open clusters?
A
Clusters that contain up to several thousand stars and are found in the disk of the galaxy
7
Q
What are globular clusters?
A
Clusters that contain hundreds of thousands of stars, closely packed together, and found mainly in the halo of the galaxy
8
Q
What are associations in terms of star clusters?
A
Loose groupings of stars of spectral type O and B, and T Tauri stars, not gravitationally bound
9
Q
How do we measure the age of a star cluster?
A
By finding the main-sequence turnoff point of its stars on an H-R diagram
10
Q
What is the age of a cluster equal to?
A
The core hydrogen fusion lifetime of the hottest, most luminous stars that remain on the main sequence
11
Q
How old can globular clusters be?
A
Globular clusters can be as old as about 13 billion years
12
Q
What is required to plot an H-R diagram?
A
Absolute luminosity (L) and distance to the star
13
Q
What is a challenge in measuring distance for stars?
A
Distance measurements are uncertain
14
Q
What does apparent magnitude measure in star clusters?
A
It is a measure of the absolute magnitude when all stars are at the same distance
15
Q
What is the main sequence fitting method?
A
A method to plot the H-R diagram using relative brightness of stars in the same cluster
16
Q
What is the mass-luminosity relation?
A
L is approximately proportional to the cube of the mass, L = M^3
17
Q
Where are the large mass stars located on the H-R diagram?
A
At the top left of the H-R diagram
18
Q
What do associations represent in star formation?
A
Groups of stars newly formed out of dust
19
Q
How are open clusters characterized in terms of gravity?
A
They have remained gravitationally bound for varying lengths of time
20
Q
What are globular clusters considered in terms of star populations?
A
Survivors of an older generation of stars, termed Population II
21
Q
What element is carried by iron-bearing haemoglobin in our blood?
A
Oxygen
22
Q
What forms the backbone of proteins, fats, and carbohydrates in our cells?
A
Chains of carbon and nitrogen
23
Q
Which elements strengthen our bones?
A
Calcium
24
Q
What ions moderate communications in the nervous system?
A
Sodium and potassium ions
25
What is the origin of the elements in our bodies?
Elements created by stars
26
Which elements were produced in the Big Bang?
Hydrogen and helium
27
What is the age of the Earth in millions of years?
4500 million years
28
What types of stars are found in young open clusters?
Massive, very bright, and very hot stars
29
What do the youngest star clusters suggest about their formation?
Formed out of clouds of dust and gas
30
Name the three distinct regions of the Triffid nebula.
* Emission nebula
* Reflection nebula
* Extinction or Dark nebulae
31
What characterizes an emission nebula?
Red/pink region ionized by energetic photons from a hot star
32
What gives the reflection nebula its blue color?
Scattering of light from nearby stars off dust grains
33
What are dark nebulae characterized by?
Dust absorbs light, cutting out light from stars behind
34
What happens when a large molecular cloud begins to collapse?
Gravity pulls gas toward densest regions, fragmenting it into smaller pieces
35
What source of heat is released during the contraction of a cloud fragment?
Gravitational potential energy
36
What is the temperature of the cloud during early star formation?
Below 100 K
37
What happens to the central temperature and pressure during the contraction of a cloud fragment?
They begin to rise dramatically
38
What is a protostar?
The clump of gas that will become a new star
39
What happens to the rotation of a protostar as it contracts?
It rotates faster due to conservation of angular momentum
40
What is the core condition required for a protostar to become a true star?
Core temperature reaches 10 million K
41
What characterizes the transition from protostar to main-sequence star?
Energy balance achieved through hydrogen fusion
42
How long does it take a high-mass protostar to become a main-sequence star?
About a million years or less
43
How long does a star like our Sun take to transition from protostar to main-sequence star?
About 50 million years
44
What role do jets play in the formation of stars?
Help clear away gas cocoon, revealing the protostar
45
What is the effect of strong magnetic fields on protostars?
Channel jets and generate a strong protostellar wind
46
True or False: Protostars are true stars because their cores are hot enough for nuclear fusion.
False
47
What does the root of the word astronomy come from?
The Greek word for 'star'.
48
Why is the Sun considered important to life on Earth?
It is the source of virtually all light, heat, and energy reaching Earth.
49
What process generates the energy that supports life on Earth?
Nuclear fusion.
50
How did ancient peoples view the Sun?
Some worshipped it as a god and created mythologies to explain its rise and set.
51
What did ancient thinkers believe the Sun was composed of?
Some type of fire, such as burning coal or wood.
52
What was the 19th-century idea about how the Sun generates energy?
Gravitational contraction (or Kelvin-Helmholtz contraction).
53
What flaw did geologists point out regarding gravitational contraction?
Earth is far older than 25 million years, which means gravitational contraction cannot account for the Sun's energy generation.
54
What significant equation did Einstein publish in 1905?
E=mc².
55
What is the main nuclear reaction in stars like the Sun?
4 hydrogen nuclei (protons) react to form a helium nucleus.
56
What particles are emitted during the proton-proton chain reaction?
Positrons and neutrinos.
57
What temperature is required for nuclear fusion to occur in stars?
10 million degrees.
58
What is the relationship between mass and luminosity in stars?
More massive stars have greater luminosity and burn hydrogen faster.
59
What processes can transfer heat from the core of a star to its surface?
* Conduction
* Convection
* Radiation
60
What happens to the Sun after about 10 billion years?
It will finish burning hydrogen in its core and start contracting.
61
What is the name of the phase when the outer layers of a star expand and it becomes a giant?
Red Giant phase.
62
What process occurs when helium nuclei fuse to form carbon in medium mass stars?
Triple-alpha process.
63
What is the helium flash?
A sudden explosion when helium burning starts in stars of between about 0.4 and 3 solar masses.
64
What are planetary nebulae?
Expanding shells of stars blown off by weak gravity at the surface of a giant.
65
Fill in the blank: The Sun generates energy through the process of _______.
nuclear fusion.
66
True or False: The Sun shines due to gravitational contraction.
False.
67
What are the life stages of a low-mass star?
Main-Sequence Stage, Red Giant Stage, Helium Core Fusion, Last Gasps
## Footnote
Each stage represents a significant phase in the life cycle of a low-mass star like the Sun.
68
What is the main characteristic of a star's main sequence stage?
Slow and steady hydrogen fusion in the core
## Footnote
This stage occupies about 90% of a star's total lifetime.
69
How long will the Sun continue to shine as a main-sequence star?
Another 5 billion years
## Footnote
The Sun has already shone for nearly 5 billion years.
70
What happens to a low-mass star when its core hydrogen is depleted?
The core begins to shrink, and the outer layers expand
## Footnote
This marks the transition into the Red Giant Stage.
71
What is the peak size and luminosity of the Sun during its red giant phase?
More than 100 times larger in radius and more than 1000 times more luminous than today
## Footnote
This expansion occurs despite the core shrinking.
72
What initiates hydrogen shell fusion in a red giant?
The surrounding shell of hydrogen becomes hot enough for fusion
## Footnote
This occurs after the core exhausts its hydrogen.
73
What is the process called that converts three helium nuclei into one carbon nucleus?
Triple-alpha reaction
## Footnote
This reaction is significant for helium core fusion.
74
What is the role of degeneracy pressure in a low-mass star?
It supports the inert core against gravitational collapse
## Footnote
It prevents the core from expanding until helium fusion ignites.
75
What occurs during a helium flash?
The temperature in the core rises rapidly, causing a spike in helium fusion rate
## Footnote
This transition marks a significant change in energy production.
76
What happens to a helium core-fusion star after it exhausts core helium?
It expands again due to helium fusion in a shell around the inert carbon core
## Footnote
This leads to the star becoming a double shell-fusion star.
77
What is the final fate of the Sun after it ejects its outer layers?
It becomes a white dwarf
## Footnote
A white dwarf is the exposed core supported by degeneracy pressure.
78
What is a planetary nebula?
A glowing shell of gas expelled from a dying star
## Footnote
The gas is ionized by the exposed core's ultraviolet radiation.
79
What do high-mass stars produce that low-mass stars cannot?
Elements heavier than helium
## Footnote
High-mass stars reach higher temperatures necessary for fusing heavier elements.
80
What is the CNO cycle?
A series of reactions in high-mass stars that fuses hydrogen into helium using carbon, nitrogen, and oxygen as catalysts
## Footnote
This cycle allows for faster hydrogen fusion compared to the proton-proton chain.
81
What happens when fusion stops in a high-mass star?
The core implodes, leading to a supernova explosion
## Footnote
This marks the dramatic end of a high-mass star's life.
82
What is the life expectancy of a high-mass star compared to a low-mass star?
High-mass stars have much shorter lifetimes
## Footnote
They evolve and die much more quickly than low-mass stars.
83
What is the proton chain?
Four hydrogen nuclei fuse into one helium-4 nucleus.
84
What allows hydrogen fusion to proceed at a much faster rate in high-mass stars?
The CNO cycle.
85
Why do high-mass stars have higher luminosities than low-mass stars?
They fuse hydrogen at a much faster rate.
86
What happens when a 25-solar-mass star runs low on hydrogen fuel?
It develops a hydrogen-fusing shell and expands outward into a supergiant.
87
What occurs to the core of a high-mass star as it runs out of hydrogen?
The core contracts, raising the temperature to fuse helium into carbon.
88
Is there a helium flash in high-mass stars?
No, high-mass stars do not experience a helium flash.
89
What happens to the inert carbon core after helium fusion stops?
It shrinks, intensifying the crush of gravity and raising core pressure and temperature.
90
What forms between the inert carbon core and the hydrogen-fusing shell?
A helium-fusing shell.
91
What is the eventual fate of a high-mass star's core after carbon fusion?
It becomes an inert core that cannot generate energy.
92
What is the significance of iron in the context of stellar cores?
Iron cannot release energy through fusion or fission.
93
What happens when iron accumulates in a stellar core?
The core can no longer generate energy, leading to a collapse.
94
What event occurs when degeneracy pressure in an iron core is overcome?
A supernova explosion.
95
What is formed after a supernova explosion?
A neutron star.
96
What happens to the electrons in a collapsing iron core?
They combine with protons to form neutrons.
97
How does the gravitational collapse of a core release energy?
It drives the outer layers off into space during a supernova.
98
True or False: High-mass stars have a longer lifespan than low-mass stars.
False.
99
Fill in the blank: The core temperature must reach _______ to fuse carbon into heavier elements.
600 million K.
100
What happens to the core pressure when iron accumulates?
The core pressure continues to increase until degeneracy pressure can no longer support it.
101
What is the mass comparison of the iron core at collapse?
It has a mass comparable to that of the Sun.
102
What is a potential outcome if the neutron star's mass is too large?
It may collapse into a black hole.
103
104
What is a neutron star?
A neutron star is the ball of neutrons created by the collapse of the iron core in a massive star supernova.
105
What is the typical radius of a neutron star?
Approximately 10 kilometres.
106
How does a neutron star resist the force of gravity?
With neutron degeneracy pressure.
107
What is the escape velocity at the surface of a neutron star?
About half the speed of light.
108
What would happen to a human body on the surface of a neutron star?
It would be squashed into a microscopically thin pancake of subatomic particles.
109
What would a paper clip made of neutron star material weigh?
It would outweigh Mount Everest.
110
What happens when neutron star material falls through the Earth?
It would drill holes through the Earth and reach the center before coming to rest.
111
What is the mass comparison of a neutron star to Earth?
A neutron star is about 300,000 times as massive as Earth.
112
Who discovered the first observational evidence of neutron stars?
Jocelyn Bell in 1967.
113
What is a pulsar?
A rapidly pulsing radio source that is a type of neutron star.
114
What was the initial name given to pulsars by astronomers?
'LGM' for Little Green Men.
115
What causes the pulsations of a pulsar?
The rapid spinning of the neutron star and the alignment of its magnetic poles.
116
True or False: All pulsars are neutron stars.
True.
117
True or False: All neutron stars are pulsars.
False.
118
What is the maximum spin rate of a white dwarf?
About once per second.
119
What is the maximum spin rate observed for some pulsars?
625 times per second.
120
What types of emissions can pulsars produce?
* Light * Radio waves * X-rays * Gamma rays
121
What is a 'glitch' in the context of pulsars?
An occasional sudden increase in the frequency of the pulsar's emissions.
122
What is a binary star system?
A system where two stars orbit around a common center of mass.
123
What is the relationship between mass and neutron stars in binary systems?
If the mass is less than about 3 solar masses, it should be a neutron star.
124
What is HZ Hercules in relation to pulsars?
It is a companion to the pulsar Hercules X-1, observed as a variable star.
125
What phenomenon occurs when matter falls into a neutron star?
X-ray bursts.
126
What evidence did Hulse and Taylor provide in 1974?
They provided the first evidence for gravitational waves through observations of a binary pulsar.
127
What occurs in a binary system that emits gravitational waves?
The shape of the mass distribution changes as it orbits.
128
Fill in the blank: Pulsars are neutron stars left behind by _______.
[supernova explosions]
129
What happens to a pulsar's rotation rate as it ages?
It gradually slows down.
130
What is a black hole?
A black hole is an object with a gravitational pull so strong that nothing, not even light, can escape from it.
131
What determines the escape velocity of an object?
The escape velocity depends on the strength of gravity, which is influenced by the object's mass and size.
132
What happens to the escape velocity as an object's size decreases?
As the size of an object decreases, its gravity becomes stronger and its escape velocity increases.
133
What is spacetime?
Spacetime is a four-dimensional continuum where space and time are interconnected, as described by Einstein's general theory of relativity.
134
What analogy is used to explain the curvature of spacetime?
A two-dimensional rubber sheet analogy is used, where the sheet is flat far from mass and curves near massive objects.
135
What is the event horizon?
The event horizon is the boundary around a black hole at which the escape velocity equals the speed of light.
136
What occurs at the event horizon?
Nothing that passes within the event horizon can ever escape, marking a point of no return.
137
What is the Schwarzschild radius?
The Schwarzschild radius is the radius of the event horizon of a black hole, depending only on its mass.
138
What is the Schwarzschild radius of a black hole with the mass of the Sun?
About 3 km.
139
What happens to a stellar core when it collapses into a black hole?
It becomes a black hole when it shrinks to a size smaller than its Schwarzschild radius.
140
What is a singularity?
A singularity is a point in a black hole where matter is crushed to an infinitely tiny and dense point.
141
What are the two theories that provide different predictions about singularities?
* Einstein's general theory of relativity
* Quantum physics
142
What are the observable properties of black holes?
* Mass
* Charge
* Angular momentum
143
Why are black holes considered not directly observable?
Because they emit no radiation, appearing 'black'.
144
What is the expected electrical charge of black holes formed from stellar collapse?
They are expected to be electrically neutral.
145
What effects can black holes have on their surroundings?
* Gravitational attraction
* Gravitational lensing
* Acting as a center of attraction in galaxies
* Forming accretion discs with X-ray emissions
146
What is Cygnus X-1?
A binary star system where a supergiant O star orbits a companion that is a potential black hole.
147
What is the significance of gamma-ray bursts in relation to black holes?
They may originate from black holes through neutron star mergers or supernova explosions leading to black hole formation.
148
True or False: A black hole can be observed directly.
False.
149
What is the luminosity increase of Type I supernovae compared to the Sun?
About 4 billion times as luminous as the Sun.
150
How quickly do Type I supernovae decline in luminosity after their peak?
They decline very rapidly in a few days, then fade more slowly over several hundred days.
151
What causes a Type I supernova to occur?
A white dwarf in a binary system accretes mass from a red giant companion, exceeds the Chandrasekhar limit, and collapses.
152
What happens to the carbon in the core of a Type I supernova?
It undergoes nuclear fusion, leading to an explosion.
153
What kind of spectral lines are observed in Type I supernovae?
Weak hydrogen lines.
154
Why are Type I supernovae considered standard candles?
They are of the same mass and will have equal intrinsic brightness.
155
What is the relationship used to calculate Hubble's constant?
Hubble's constant H = velocity (V) divided by distance (D).
156
What unexpected result has been found regarding distant galaxies and Type I supernovae?
Distant galaxies are accelerating away from us.
157
How bright are Type II supernovae compared to the Sun?
About 0.6 billion times the solar luminosity.
158
What is the primary characteristic of Type II supernovae's spectrum?
They contain hydrogen lines.
159
What occurs to the core of a massive giant star during a Type II supernova?
It collapses to become a neutron star.
160
What is emitted during the collapse of a core in a Type II supernova?
Neutrinos.
161
What is the remnant of a Type I supernova?
Type I supernovae do not leave remnant neutron stars.
162
What are supernova remnants observed as?
A cloud of gas expanding away from the site of the explosion.
163
What type of radiation is emitted by supernova remnants?
X-rays and radio waves.
164
What was significant about supernova SN 1987A?
It was the first supernova in 400 years visible to the naked eye.
165
What was the peak magnitude of SN 1987A?
2.9.
166
What was detected 18 hours before the light from SN 1987A was observed?
A burst of 19 neutrinos.
167
What was the star that exploded in SN 1987A identified as?
Sanduleak -SK-69o 202.
168
What type of supernova was SN 1987A classified as?
Type II.
169
What radioactive elements were observed in the explosion of SN 1987A?
Cobalt and nickel.
170
Approximately how much nickel was produced in SN 1987A?
About 20,000 times the mass of the Earth.
171
What is expected to happen to the core of SN 1987A?
It is expected to become a neutron star.
172
Fill in the blank: Type II supernovae are produced as an explosive end to the lives of very ______ stars.
massive giant
173
What is a white dwarf?
The exposed core of a star that has died and shed its outer layers in a planetary nebula
174
How does the temperature of a white dwarf change over time?
It is hot when it first forms but slowly cools with time
175
What is the typical size comparison of a white dwarf to Earth?
White dwarfs have masses like those of stars but sizes like that of Earth
176
What type of light can the hottest white dwarfs emit?
High-energy light such as ultraviolet and X-rays
177
What keeps a white dwarf stable against gravitational collapse?
Electron degeneracy pressure
178
What is electron degeneracy pressure?
Pressure arising from closely packed electrons that supports white dwarfs against gravity
179
What does the composition of a white dwarf reflect?
The products of the star’s final fusion stage
180
What is the typical composition of a white dwarf left behind by a 1MSun star?
Mostly carbon
181
What happens to the density of a white dwarf as its mass increases?
More massive white dwarfs are smaller in size and have greater density
182
What is the weight of a teaspoon of white dwarf material if brought to Earth?
Several tons, equivalent to the weight of a small truck
183
What is the Chandrasekhar limit?
The maximum mass of a white dwarf, approximately 1.4MSun
184
True or False: No white dwarf can exceed the Chandrasekhar limit.
True
185
What is gravitational redshift?
The phenomenon where photons escaping a star lose energy due to its gravity
186
What happens if a rocket does not have enough initial energy to escape Earth?
It falls back to Earth
187
What is the Roche surface in binary stars?
The region around each star where matter is bound by gravitational attraction
188
What can happen when a star in a binary system expands to become a giant?
The companion star can suck up some of the matter
189
What is a Type I Supernova?
A violent nuclear explosion that occurs when a white dwarf exceeds the Chandrasekhar limit
190
What is a nova?
A less dramatic event where hydrogen gas forms an accretion disc around a white dwarf and leads to a nuclear explosion
191
Fill in the blank: A nova can be _______ times brighter than the sun.
100,000
192
What happens to a white dwarf after a nova event?
It reverts to its normal white dwarf state and can undergo nova events repeatedly
