Deck 16: Stars in the Slow Lanelow-Mass Stellar Evolution

Question 1

Which star spends the longest time as a main-sequence star?

A)
B)
C)
D)

Answer 1

Question 2

A star like the Sun will eventually become an electron degenerate white dwarf star.

Answer 2

True

Question 3

A Type I supernova is as luminous as 10 billion Suns.

Answer 3

True

Question 4

Stars with masses similar to the Sun will loose about 30 percent of their mass before they become white dwarfs.

Question 5

The evolutionary cutoff between low- and high-mass stars occurs at approximately

A)
B)
C)
D)

Question 6

The main-sequence lifetime of a star is given by the equation

A) .
B) .
C) .
D) .

Question 7

The Sun eventually could become a nova.

Question 8

When a star burns hydrogen in a shell,it will never produce as much energy (per unit time)as when it burns hydrogen in the core because the core has a higher temperature.

Question 9

If a main-sequence star's core temperature increased,fusion reaction rates would decrease because the protons would be moving faster.

Question 10

A main-sequence star is unique because

A) hydrostatic equilibrium exists at all radii.
B) energy transport occurs via convection throughout much of its interior.
C) hydrogen burning occurs in its core.
D) it emits strong surface winds.

Question 11

A low-mass star that burns helium in its core and hydrogen in a shell is more luminous than a similar star that burns only hydrogen in a shell around a dead core.

Question 12

The more massive a star,the more hydrogen it has to burn,and the longer its main-sequence lifetime will be.

Question 13

Pressure from degenerate electrons keeps the core of a red giant star from collapsing.

Question 14

The percent of hydrogen in the Sun's core today is roughly half of what it had originally.

Question 15

Stars evolve primarily because they run out of fuel in their cores.

Question 16

What factor is most important in determining a star's position on the main sequence and subsequent evolution?

A) Temperature
B) Pressure
C) Mass
D) Radius

Question 17

Binary stars can evolve to become novae and supernovae because slight differences in mass can mean large differences in main-sequence lifetimes.

Question 18

A star will evolve through the same phases as a star.

Question 19

The Sun will become a red giant star in about 2 billion years.

Question 20

Once the core of a low-mass main-sequence star runs out of hydrogen,fusion in the star stops until the core temperature is high enough for helium fusion to begin.

Question 21

As a red giant star evolves,hydrogen shell burning proceeds increasingly faster due to

A) rotational energy from the star's rapid rotation.
B) heat released from the core's contraction.
C) pressure from the contracting envelope.
D) This is a trick question.Hydrogen actually burns increasingly slower with time.

Question 22

The Sun will likely stop being a main-sequence star in

A) 5,000 years.
B) 5 million years.
C) 500 million years.
D) 5 billion years.

Question 23

When a G2 star leaves the main sequence,

A) its luminosity and surface temperature both stay the same.
B) its luminosity and surface temperature both decrease.
C) its luminosity increases and its surface temperature decreases.
D) its luminosity and surface temperature both increase.

Question 24

What is the escape velocity from the surface of a star that has a radius of ?

A) 60 km/s
B) 120 km/s
C) 240 km/s
D) 620 km/s

Question 25

How long will a star live as a main-sequence star?

A) 12 million years
B) 1.8 billion years
C) 12 billion years
D) 180 million years

Question 26

A star's surface temperature during the horizontal branch phase is determined primarily by its

A) luminosity.
B) chemical composition.
C) magnetic field strength.
D) rotation rate.

Question 27

The luminosity of a star depends on

A) its mass,its age,and its distance.
B) its mass.
C) its age.
D) its mass and its age.

Question 28

When a star depletes its core supply of hydrogen,__________ dominates in the core and __________ dominates in the atmosphere.

A) pressure;pressure
B) pressure;gravity
C) gravity;gravity
D) gravity;pressure

Question 29

A low-mass main-sequence star's climb up the red giant branch is halted by

A) the end of hydrogen shell burning.
B) the beginning of helium fusion in the core.
C) electron-degeneracy pressure in the core.
D) instabilities in the star's expanding outer layers.

Question 30

Just as a low-mass main-sequence star runs out of fuel in its core,it grows more luminous.How is this possible?

A) It explodes.
B) It begins to fuse helium in the core.
C) Its core expands as it runs out of fuel.
D) Its core shrinks,bringing more hydrogen fuel into the burning region.

Question 31

During which phase of the evolution of a low-mass star does it have two separate regions of nuclear burning occurring in its interior?

A) main sequence
B) red giant
C) horizontal branch
D) white dwarf

Question 32

If the Milky Way formed stars at approximately a constant rate over the last 14 billion years,what fraction of the M stars that ever formed in it can still be found as main-sequence stars today? Note that M stars have a mass of approximately .

A) 10 percent
B) 33 percent
C) 50 percent
D) 100 percent

Question 33

A low-mass red giant star's energy comes from

A) hydrogen burning to helium in its core.
B) helium burning to carbon in its core.
C) hydrogen burning to helium in a shell surrounding its core.
D) helium burning to carbon in a shell surrounding its core.

Question 34

When a low-mass star becomes an AGB star and has a temperature of 3,300 K,at what wavelength will it shine the brightest?

A) 650 nm,red visible
B) 880 nm,infrared
C) 1 mm,microwave
D) 10 m,radio

Question 35

Degenerate refers to a state of matter at

A) high temperature.
B) high density.
C) high luminosity.
D) high mass.

Question 36

Asymptotic giant branch (AGB)stars have high-mass loss rates because

A) they are rotating quickly.
B) they have weak magnetic fields.
C) they have strong winds.
D) they have low surface gravity.

Question 37

When helium fusion begins in the core of a red giant star,the situation quickly gets out of control because electron-degeneracy pressure does not respond to changes in

A) luminosity.
B) density.
C) gravity.
D) temperature.

Question 38

Helium burns in the core of a horizontal branch star via __________ and produces __________.

A) the triple-alpha reaction;carbon
B) the proton-proton chain;lithium
C) the triple-alpha reaction;oxygen
D) the proton-proton chain;iron

Question 39

What is the radius of a red giant star that has a temperature of and a temperature of 4,000 K? (Note that the temperature of the Sun is 5,800 K. )

A)
B)
C)
D)

Question 40

As a main-sequence star burns its core supply of hydrogen,what happens?

A) Helium begins to fuse throughout the core.
B) Helium fuses in a shell surrounding the core.
C) Helium fusion takes place only at the very center of the core,where temperature and pressure are highest.
D) Helium builds up as ash in the core.

Question 41

What ionizes the gas in a planetary nebula and makes it visible?

A) X-ray photons emitted by a pulsar
B) Ultraviolet photons emitted by a white dwarf
C) The shock wave from a supernova
D) Hydrogen burning in the nebular gas

Question 42

Why does the core of a main-sequence star have to be hotter to burn helium into carbon than hydrogen into helium?

Question 43

Explain the two different forms of pressure that support the core of a low-mass main-sequence star and the core of a low-mass red giant star?

Question 44

How many times longer does a main-sequence star live compared to a main-sequence star?

Question 45

Calculate the main-sequence lifetimes of the following stars of different spectral types: , , , ,and .What trend do you notice in your results?

Question 46

A Type I supernova has a luminosity of approximately

A) .
B) .
C) .
D) .

Question 47

The Ring Nebula is a planetary nebula that currently has a radius of 0.4 pc and an expansion velocity of 250 km/s.Approximately how long ago did its parent star die and eject its outer layers?

A) 1,600 years ago
B) 3,200 years ago
C) 5,400 years ago
D) 28,000 years ago

Question 48

In what two ways does temperature affect the rate of nuclear reactions?

Question 49

A star in a binary system could create the following chemical element and eject it into the interstellar medium:

A) carbon
B) helium
C) iron
D) All of the above

Question 50

A star like the Sun will lose about __________ of its mass before it evolves to become a white dwarf.

A) 3 percent
B) 10 percent
C) 30 percent
D) 70 percent

Question 51

If a white dwarf could accrete matter from a binary companion at a rate of ,how long would it take before it exploded as a Type I supernova?

A) 600 thousand years
B) 20 million years
C) 200 milllion years
D) 600 million years

Question 52

A nova is the result of which explosive situation?

A) Mass transfer onto a white dwarf
B) Helium burning in a degenerate stellar core
C) A white dwarf which exceeds the Chandrasekhar limit
D) The collision of members of a binary system

Question 53

What would you need to measure about a planetary nebula to determine how long ago its parent star died?

A) The mass of the white dwarf
B) The mass and radius of the white dwarf
C) The nebula's temperature and radius
D) The nebula's radius and expansion velocity

Question 54

In a white dwarf,what is the source of pressure that halts its contraction as it cools?

A) Thermal pressure of the extremely hot gas
B) Electrons packed so closely that they become incompressible
C) Neutrons that resist being pressed further together
D) Carbon nuclei that repulse each other strongly because they each contain six protons

Question 55

A white dwarf with a temperature of 30,000 K would shine brightest at what wavelength?

A) 4 nm,X-rays
B) 100 nm,ultraviolet
C) 400 nm,blue visible
D) 1 $\mu$ m,infrared

Question 56

One star in a binary will almost always become a red giant before the other because

A) one star is always larger than the other.
B) binaries always have one star twice as massive as the other.
C) small differences in main-sequence masses yield large differences in main-sequence ages.
D) the more massive binary star always gets more mass from the less massive binary star when both are main-sequence stars.

Question 57

Consider a red giant star with a luminosity of and a radius of .Using the luminosity-temperature-radius relationship ,calculate how hot this star's surface temperature will be compared to the Sun,whose temperature is 5,800 K.

Question 58

A Type I supernova occurs when a white dwarf exceeds a mass of __________.

A)
B)
C)
D)

Question 59

What is a planetary nebula?

A) A planet surrounded by a glowing shell of gas
B) The disk of gas and dust surrounding a young star that will soon form a star system
C) The ejected envelope of a giant star surrounding the remains of a star
D) A type of young,medium-mass star

Question 60

The gas in a planetary nebula is composed of

A) primarily hydrogen from the surrounding interstellar medium.
B) primarily hydrogen from the post-asymptotic giant branch star.
C) hydrogen and elements processed in the core of the post-asymptotic giant branch star.
D) primarily helium from the post-asymptotic giant branch star.

Question 61

What is the shortest phase of evolution for a one solar mass star that we can visibly see?

Question 62

When the Sun becomes an AGB star,its radius will be approximately .If its mass at this point will be approximately the same as it is now,how will its surface gravity as an AGB star compare to its present surface gravity as a main-sequence star? Note that .

Question 63

What stops a red giant from cooling to continuously lower temperatures,and why?

Question 64

What is "degenerate" in the degenerate core of a white dwarf?

Question 65

Explain the significance of Roche lobes in a binary system.

Question 66

Why are novae thought to be recurrent?

Question 67

What types of chemical elements can low-mass stars contribute to the enrichment of the interstellar medium and how are they produced?

Question 68

How can the core of a star be degenerate with respect to the electrons but nondegenerate with respect to the nuclei?

Question 69

Consider a star's journey up the red giant branch.Its luminosity will change from to nearly .How will its temperature and radius change as the star ascends? (Recall that . )