Deck 14: Stellar Evolution

Question 1

The most important property that determines the evolution of a star is its

A) temperature.
B) composition.
C) mass.
D) location.

Answer 1

mass.

Question 2

For a star like the Sun, the gravitational collapse of the interstellar cloud lasted for about ______________ and stopped with the ignition of the fusion reaction.

A) 50-100 billion years
B) 5-10 billion years
C) 1 billion years
D) 100 million years
E) 1-10 million years

Answer 2

1-10 million years

Question 3

____ is the most significant force that determines the evolution of stars.

A) Temperature
B) Luminosity
C) Energy
D) Gravity

Answer 3

Gravity

Question 4

Why does a high-mass star evolve differently from a low-mass star?

A) It can fuse additional elements because its core can get hotter.
B) It has more material to burn so it can last longer.
C) It is so bright that it drives material in space away from it so it can't gather up more fuel.
D) It has a lower gravity so it can't pull in more fuel from space.
E) The statement is false. High and low-mass stars evolve the same way.

Question 5

The Sun's evolution from youngest to oldest stage is

A) white dwarf, red giant, main sequence, protostar.
B) red giant, main sequence, white dwarf, protostar.
C) protostar, red giant, main sequence, white dwarf.
D) protostar, main sequence, red giant, white dwarf.

Question 6

Brown dwarfs are

A) large terrestrial planets.
B) objects massive enough to fuse deuterium but not massive enough to sustain hydrogen fusion.
C) very low-mass main sequence stars.
D) what is left over after a massive star ejects most of its material through a supernova.

Question 7

When do we say that a star is born?

A) when the interstellar cloud collapses
B) when the interstellar matter achieves the Jeans instability
C) when fusion of hydrogen atoms into helium atoms starts
D) when the star leaves the main sequence

Question 8

What stars form the slowest?

A) O and B
B) A and F
C) G and A
D) K and M

Question 9

Protostars shine brightest in

A) radio waves.
B) infrared spectrum.
C) visible spectrum.
D) X-ray.

Question 10

The Sun formed from the gravitational collapse of a cold __________.

A) red giant
B) planet
C) planetary nebula
D) interstellar cloud

Question 11

A protostar becomes a main sequence star when it ________________.

A) starts fusing helium
B) starts fusing hydrogen to helium
C) starts fusing heavier elements
D) starts glowing with infrared light

Question 12

The typical temperature of an interstellar cloud that could collapse to a protostar is about _______.

A) 1,500 K
B) 1,000 K
C) 300 K
D) 10 K

Question 13

Protostars are observable by radio telescopes but hard to detect in visible light because they have _____ and are ____.

A) low surface temperature; very distant
B) small size; very hot
C) low surface temperature; surrounded by dust
D) small size; very distant

Question 14

A ____ is a region where jets of gas from young stars impact and heat the gas surrounding the young star.

A) planetary nebula
B) bok globule
C) bipolar outflow
D) T Tauri star

Question 15

In the H-R diagram a T Tauri star will be located ___________.

A) near the upper right corner
B) near the upper left corner
C) near the bottom left corner
D) below the main sequence
E) on the right hand side and a little above the main sequence

Question 16

A protostar is not _____.

A) producing energy
B) collapsing
C) in hydrostatic equilibrium
D) heating up

Question 17

Protostars initially do not experience hydrogen fusion. How does their temperature increase?

A) the light from nearby stars
B) gravitational energy from infalling material
C) fusion of hydrogen into helium
D) energy from their magnetic fields

Question 18

Because protostars are at a low temperature and surrounded by dust and gas, astronomers must observe them with ____________.

A) radar
B) ultraviolet telescopes
C) infrared and radio telescopes
D) gamma ray telescopes

Question 19

What is a T Tauri star?

A) any variable star
B) a red giant with a peculiar spectrum
C) any star found in the constellation of Taurus
D) a young star that exhibits variable light and outflowing gas

Question 20

A star enters the main sequence when _________________.

A) nuclear fuel in its core can supply enough energy to stop its collapse
B) it collapses, and its envelope becomes degenerate
C) it stops fusing nuclear fuel in its core and starts to expand
D) it forms planets

Question 21

What makes a gas cloud contract to form stars?

A) The cloud's magnetic field draws material together.
B) The dust in the cloud is pulled together by static electricity.
C) All parts of the cloud are gravitationally attracted to all other parts, collapsing the cloud.
D) Pressure from meteor collisions pushes the cloud together.
E) Uranium atoms attract lead atoms by nuclear fusion.

Question 22

What makes a star stop contracting?

A) Its magnetic field pushes back against the force of gravity.
B) The dust in it gets packed so tightly that it cannot continue to contract.
C) Its gravity gets too strong for it to continue contracting.
D) It gets hot enough that its pressure builds up, pushing back against the force of gravity.
E) It gets cool enough that it freezes, and the resulting ice is hard enough to push back against gravity.

Question 23

From what do stars form?

A) globular clusters
B) open clusters
C) black holes
D) planetary nebulas
E) interstellar clouds

Question 24

The lifetime of a star is dependent on its ______.

A) mass
B) volume
C) luminosity
D) temperature

Question 25

The Sun will leave the main sequence in about ______ years from now.

A) 5 million
B) 100 billion
C) 100 million
D) 5 billion

Question 26

If a star is in hydrostatic equilibrium

A) it is in a stable binary orbit.
B) it is generating energy at the same rate everywhere.
C) it is near the end of its life.
D) it must be losing mass.
E) its radiation pressure outwards and gravitational forces inwards are in balance.

Question 27

In which stage of a star's evolutionary cycle does it spend the most time?

A) the pre-main sequence
B) the main sequence
C) the post-main sequence
D) It depends on the mass of the star.

Question 28

What characteristic do all stars on the main sequence share?

A) They all have the same size.
B) They all have the same luminosity.
C) They all have the same temperature.
D) They are all fusing hydrogen into helium in their cores.
E) They will all go through a helium flash in the future.

Question 29

The main source of energy in main sequence stars is ________________.

A) fusion of hydrogen to helium
B) gravity
C) the triple alpha process
D) the chemical reaction between hydrogen and helium

Question 30

Hydrostatic equilibrium is the balance between _____ of a star and _____.

A) the internal pressure; energy production
B) hydrogen fusion; temperature
C) the size; energy production
D) the internal pressure; gravity

Question 31

The CNO cycle produces energy by fusing

A) neon into magnesium and oxygen.
B) hydrogen into helium.
C) carbon and nitrogen into oxygen.
D) silicon into iron.

Question 32

During a star's main sequence portion of its life it does not change size appreciably. This observation indicates that

A) the Sun produces more energy than it radiates into space.
B) the Sun produces less energy than it radiates into space.
C) the Sun produces about the same amount of energy as it radiates into space.

Question 33

A star whose mass is 5 times larger than the Sun's and whose luminosity is 100 times larger than the Sun's has a main sequence lifetime about

A) 5 times longer than the Sun's.
B) 500 times longer than the Sun's.
C) 5 times shorter than the Sun's.
D) 100 times shorter than the Sun's.
E) 20 times shorter than the Sun's.

Question 34

When a star has stopped contracting and settled down, where is it in the H-R diagram?

A) on the main sequence
B) below the main sequence in the lower left
C) in the upper right as a red giant
D) It is not on the H-R diagram at that time
E) in the instability strip

Question 35

What fuel do stars on the main sequence burn?

A) hydrogen
B) helium
C) carbon
D) iron
E) uranium

Question 36

Why do elements fuse only in a star's core?

A) The fuel settles to the core.
B) Only the core is hot enough for fusion.
C) Only the core spins fast enough.
D) The statement is incorrect. Fusion occurs just below the surface.
E) None of these choices is correct.

Question 37

What makes a star shine?

A) reflected light from the galaxy
B) radioactive decay of elements in its core
C) nuclear fusion of light elements
D) nuclear fission of heavy elements
E) None of these choices is correct.

Question 38

What determines how long a star stays on the main sequence?

A) its temperature and mass
B) its luminosity and radius
C) its mass and luminosity
D) its radius and mass

Question 39

What determines how rapidly a star burns up its fuel?

A) its mass
B) its luminosity
C) the pressure in its core
D) the temperature in its core
E) All of these choices are correct.

Question 40

What of the following most directly determines how much fuel a star has?

A) its density
B) its mass
C) its temperature
D) its luminosity
E) its speed of rotation

Question 41

When the outer envelope of a red giant is ejected, the remaining exposed core of a low mass star is called a

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

Question 42

Which of the following statements about the "helium flash" is correct?

A) It does not occur in high-mass stars.
B) It does not occur in stars smaller than 0.5 solar masses.
C) It marks the end of the red giant stage for a star like the Sun.
D) It releases enough energy to change the degenerate gas in the core to normal gas.
E) All of these choices are correct.

Question 43

After a star leaves the main sequence, ______________________.

A) it continues to fuse hydrogen into helium in its core
B) it now fuses hydrogen into helium in a shell outside the core
C) it no longer fuses hydrogen into helium anywhere inside the star
D) all hydrogen in the star has been fused, and helium fusion begins

Question 44

When a star moves off the main sequence and becomes a red giant it is brighter because

A) the star moves closer to Earth.
B) the size of the star increases.
C) the surface temperature increases.
D) the star's mass increases.

Question 45

The triple alpha process produces energy by fusing ____ into ____.

A) helium; carbon
B) hydrogen; helium
C) oxygen; carbon
D) oxygen and carbon; carbon dioxide
E) carbon and nitrogen; cyanogen

Question 46

After the hydrogen in the star's core is depleted the core

A) shrinks and cools down.
B) shrinks and heats up.
C) expands and cools down.
D) expands and heats up.

Question 47

What happens to a star's core as the hydrogen there is used up?

A) Nothing. It just turns to helium.
B) It expands and cools.
C) It contracts and cools.
D) It contracts and heats.
E) As the helium accumulates, the core rises to the surface of the star and escapes into space.

Question 48

What happens to the star's outer layers as the fuel in its core is used up?

A) They shrink and cool.
B) They shrink and heat up.
C) They expand and cool.
D) They expand and heat up.
E) Nothing. Only the interior changes.

Question 49

Why does the star's core get hotter as the core shrinks?

A) The fusing elements settle there to liberate their heat.
B) The core is compressed and compression heats a gas.
C) The core spins faster and friction heats it.
D) The statement is false. A shrinking core cools.
E) None of these choices is correct.

Question 50

What kind of object does a main sequence star become on first using up its core hydrogen?

A) a white dwarf
B) a protostar
C) a supernova
D) a planetary nebula
E) a red giant

Question 51

Stars like the Sun probably do not form iron cores during their evolution because

A) all the iron is ejected when they become planetary nebulas.
B) their cores never get hot enough for them to make iron by nucleosynthesis.
C) the iron they make by nucleosynthesis is all fused into uranium.
D) their strong magnetic fields keep their iron in their atmospheres.
E) None of these choices is correct.

Question 52

As a star like the Sun evolves into a red giant, its core

A) expands and cools.
B) contracts and heats.
C) expands and heats.
D) turns into iron.
E) turns into uranium.

Question 53

A star leaves the main sequence when

A) nuclear fuel in its core can supply enough energy to stop its collapse.
B) it collapses, and its envelope becomes degenerate.
C) it stops fusing hydrogen in its core and starts to expand.
D) it forms planets.

Question 54

When a massive star begins to run out of hydrogen to fuse, its core ____________.

A) expands and cools
B) contracts and heats
C) expands and heats
D) contracts and cools

Question 55

When a massive star begins to run out of hydrogen to fuse, its outer layers of gas ____________.

A) expand and cool
B) contract and heat
C) expand and heat
D) contract and cool

Question 56

Why can high-mass stars "burn" helium more easily than low-mass stars?

A) A high-mass star's core is already very hot, so it only needs to compress its core a little to burn helium.
B) High-mass stars are already burning helium on the main sequence.
C) Low-mass stars have proportionately less helium than high-mass stars.
D) This statement is false. It is much harder for high-mass stars to burn helium.

Question 57

The period-luminosity law of pulsating variable stars indicates that

A) the more slowly a star pulsates, the more luminous it is.
B) the faster a star pulsates, the more luminous it is.
C) the period of pulsation is independent of luminosity.
D) None of these choices is correct.

Question 58

What makes variable stars useful in determining star distances?

A) Their exact location in the H-R diagram is known.
B) They are brighter than other stars.
C) Their luminosity can be determined from their pulsation period.
D) They are easier to spot than ordinary stars.

Question 59

High-mass stars become ____ variables when they cross the instability strip, while low-mass stars become ____ variables.

A) Cepheid; RR Lyrae
B) RR Lyrae; Cepheid
C) ZZ Ceti; RR Lyrae
D) Cepheid; T Tauri
E) T Tauri; Cepheid

Question 60

The light curve of a large Cepheid variable would typically show pulsations in luminosity ____________.

A) every 6 minutes
B) every 6 hours
C) every 60 days
D) every 6 months
E) every 6 years

Question 61

What is a "pulsating star"?

A) a rotating neutron star that emits radio waves in a narrow beam
B) a star whose luminosity changes as it regularly expands and contracts
C) a planetary nebula
D) a star whose mass changes as it comes into contact with another star

Question 62

Which of the following statements about planetary nebulas is correct?

A) They are shells of glowing gas and dust ejected by dying Sun-like stars.
B) They contain flakes of carbon and silicon material.
C) They expand at a typical rate of 20 kilometers per second.
D) Their shape can be very irregular.
E) All of these choices are correct.

Question 63

What is a "planetary nebula"?

A) It is the disk of gas around a young star.
B) It is the cloud from which protostars form.
C) It is a shell of gas ejected from a star late in its life.
D) It is what is left when a white dwarf star explodes as a supernova.

Question 64

Which of the following elements in your body is formed in stars?

A) carbon
B) oxygen
C) calcium
D) iron
E) All of these choices are correct.

Question 65

The process in which two or more lighter elements combine to form a single heavier element is called

A) nucleosynthesis.
B) photodisintegration.
C) neutronization.
D) fission.

Question 66

Which of the following statements apply in the final moments of the life of high-mass stars?

A) Their outer layer is mainly hydrogen and helium.
B) Around their cores, they have a series of nested shells, each made of a heavier element than the one surrounding it.
C) They have iron cores.
D) The core temperature is about 2 billion degrees.
E) All of these choices are correct.

Question 67

Which of the following statements about the evolution of high-mass stars is NOT correct?

A) High-mass stars evolve much faster than low-mass stars.
B) High-mass stars can fuse elements heavier than helium in their core.
C) High-mass stars stop fusing elements once they reach a carbon-filled core.
D) High-mass stars do not have a helium flash.
E) The life of a high-mass star ends with a supernova explosion.

Question 68

How do most of the heavier elements up to iron form in the universe?

A) in supernova explosions
B) by nucleosynthesis in the cores of massive stars
C) in the original interstellar clouds
D) in the cores of protostars

Question 69

Where do most of the elements heavier than iron form?

A) in the interior of stars
B) in the interior of high-mass stars
C) in supernova explosions
D) in the interstellar clouds

Question 70

The last fusion product possible in stars is _________ because _________.

A) lead, fusing lead nuclei absorbs energy; it does not liberate it
B) iron, fusing iron nuclei absorbs energy; it does not liberate it
C) iron; no stars are hot enough in their cores to fuse iron nuclei
D) carbon; no stars are hot enough in their cores to fuse carbon nuclei

Question 71

Supernova remnants ________.

A) initially expand at thousands of km/s
B) may contain up to 10 solar masses of material ejected from the star
C) are important for mixing material into the interstellar medium
D) All of these choices are correct.

Question 72

What makes a high-mass star's core collapse?

A) Energy from its outer layers compresses its core.
B) The only thing that can make a star's core collapse is a collision with another star.
C) Massive stars develop iron cores that cannot fuse anymore, so the core collapses under gravity.
D) Massive stars' cores don't collapse. They expand and become planetary nebulas.

Question 73

What can be observed from Earth when a supernova explodes?

A) photons and neutrinos
B) electrons and protons
C) photons and neutrons
D) neutrons and neutrinos

Question 74

What allows a high-mass star to fuse different elements from a low-mass star?

A) Its greater mass means that it contains more elements.
B) More mass means a stronger magnetic field that helps heavier elements fuse.
C) More mass means more compression and thus a hotter core that allows heavier elements to fuse.
D) High-mass stars spin slower and thus do not mix their fuels as well.
E) The statement is false. Low-mass and high-mass stars can fuse the same elements.

Question 75

How do astronomers test models of stellar evolution?

A) by comparing the paths in the H-R diagram predicted by models with the H-R diagrams of star clusters
B) by measuring the number of stars in a cluster and comparing with the number predicted by the models
C) by recording the properties of a star over an extended period of time
D) by assuming that all the stars in our galaxy formed at the same time, and comparing with predictions of the models

Question 76

Which of the following statements regarding the H-R diagrams of star clusters is NOT correct?

A) A very young cluster will have stars that lie in the right hand side and a little above the main sequence.
B) A very old cluster will show a turn-off point and will have many red and yellow giant stars.
C) A very young cluster will not show a turn-off point.
D) A very old cluster will have many stars in the upper left corner of the H-R diagram.
E) A very young cluster will not have all its stars on the main sequence.

Question 77

What becomes of the heavy elements produced by fusion in low-mass stars?

A) They are forever trapped in the core of the star.
B) When the star goes supernova, they are sucked into the neutron star or black hole.
C) Low-mass stars do not produce heavy elements.
D) At the end of the star's life, they are dredged up by convection and pushed outward by photons.
E) They are blasted outward in a violent explosion.

Question 78

Which of the following statements is true?

A) Planetary nebulae are an important source of interstellar carbon and nitrogen.
B) Low-mass stars can fuse heavier elements by the triple-alpha process and neutron capture.
C) Low-mass stars cannot produce neon.
D) All of these choices are correct.

Question 79

Which of the following elements is produced by high-mass stars but not low-mass stars?

A) Nitrogen
B) Carbon
C) Strontium
D) Rubidium
E) Lead

Question 80

The gravitational collapse of an interstellar cloud can be triggered by a collision with another cloud.