Deck 17: Evolution of High-Mass Stars

Question 1

What causes massive stars to lose mass at a high rate through stellar winds?

A) radiation pressure
B) high magnetic fields
C) rapid rotation
D) carbon fusion
E) emission of neutrinos

Answer 1

radiation pressure

Question 2

In the CNO cycle, carbon is used as a catalyst for the fusion of hydrogen into helium. This means that

A) three helium nuclei fuse to form carbon.
B) carbon facilitates the reaction but is not consumed in it.
C) carbon boosts the energy from the reaction, which is why massive stars are luminous.
D) carbon breaks apart into three helium nuclei.
E) the reaction produces carbon nuclei in addition to helium.

Answer 2

carbon facilitates the reaction but is not consumed in it.

Question 3

What mechanism drives the pulsations in Cepheid variables?

A) changes in the rate of core nuclear reactions
B) the formation and destruction of sunspots
C) the ionization and recombination of hydrogen
D) the ionization and recombination of helium
E) large rates of mass loss

Answer 3

the ionization and recombination of helium

Question 4

Each kilogram of hydrogen that fuses into helium releases about 6 * 10¹⁴ joules of energy.How many tons of hydrogen are fused each second to power a massive main-sequence star with a luminosity of 100 L_SUN? (Note that 1 L_SUN = 4 *10²⁶ joule/second and 1 ton= 10³ kg.)

A) 2*10⁶ tons
B) 7 * 10⁷ tons
C) 2 *10⁹ tons
D) 7 *10¹⁰ tons
E) 2 *10¹¹ tons

Question 5

Which of these fusion reactions begins first in the core of a massive star?

A) silicon fusion to iron
B) neon fusion to magnesium
C) carbon fusion to neon
D) helium fusion to carbon
E) hydrogen fusion to helium

Question 6

The luminosity of a Cepheid star varies in time because

A) the entire star pulsates from its core to its surface.
B) the outer envelope of the star contracts and expands radially.
C) the star rotates too quickly.
D) the star is too massive to be stable.
E) the star undergoes changing chemical reactions on its surface.

Question 7

A main-sequence star of 25 solar masses has about 25 times the luminosity of a 10-solar-mass star (recall the mass-luminosity relation presented in the previous chapter).This is because the more massive star

A) has a hotter core, and therefore nuclear burning proceeds more rapidly.
B) has more convection in its core, which heats the material there.
C) has more hydrogen to burn.
D) has more carbon available, which speeds up the CNO cycle.
E) is probably younger than the 10-solar-mass star.

Question 8

The dominant mechanism by which high-mass stars generate energy on the main sequence is called

A) the proton-proton chain.
B) the carbon-carbon reaction.
C) the triple-alpha process.
D) the CNO cycle.
E) neutrino cooling.

Question 9

What is one way in which high-mass stars differ from low-mass stars?

A) They are found at cooler temperatures on the main sequence.
B) They fuse carbon through silicon without leaving the main sequence.
C) Convection is important in their cores, as it mixes helium throughout the core.
D) They turn into red giants explosively.
E) Most of their energy is produced by fission rather than fusion.

Question 10

In the post-main-sequence stages, high-mass stars follow quasi-horizontal paths in the H-R diagram.This means that

A) their luminosity increases because they expand.
B) their color gets redder because they expand.
C) their surface temperature stays about the same because their luminosity stays about the same.
D) they become supernovae immediately after leaving the main sequence.
E) they collapse and become very small in size.

Question 11

The fundamental stellar property that determines the major evolutionary differences in the life history of stars is

A) distance from Earth.
B) mass.
C) location within a galaxy.
D) rotation.
E) presence/absence of planets around stars.

Question 12

As a high-mass main-sequence star evolves off the main sequence, it follows a ________ on the H-R diagram.

A) nearly vertical path
B) path of constant radius
C) nearly horizontal path
D) path of declining luminosity
E) path of increasing temperature

Question 13

The CNO cycle is the more efficient mechanism for hydrogen fusion only in stars more massive than 1.3-1.5 M_SUN because of the greater ________ their cores.

A) concentration of heavy elements like carbon in
B) turbulence in
C) abundance of hydrogen in
D) temperature of
E) rotation speed of

Question 14

An iron core cannot support a massive main-sequence star because iron

A) has low nuclear binding energy.
B) is not present in stellar interiors.
C) supplies too much pressure.
D) fusion occurs only in a degenerate core.
E) cannot generate energy when fusing heavier nuclei.

Question 15

The nuclear fusion reactions involved in the CNO cycle require much higher temperatures than the reactions within the proton-proton chain because

A) carbon nuclei can exist only at extremely high temperatures.
B) reactions involving a catalyst can only occur at higher temperatures.
C) low-mass stars do not have convective cores.
D) neutrinos can only survive at temperatures where the CNO cycle is possible.
E) nuclei with higher number of protons have a greater repulsive barrier against protons,
So particles need to move fast to overcome it.

Question 16

If you measure the average brightness and pulsation period of a classical Cepheid variable star, you can also determine its

A) age.
B) rotation period.
C) distance.
D) mass.
E) composition.

Question 17

The main difference between classical Cepheids and RR Lyrae stars is

A) their masses.
B) that Cepheids form at much greater distances from Earth.
C) that RR Lyrae were discovered much earlier than classical Cepheids.
D) their pulsation mechanisms.
E) that classical Cepheids obey a period-luminosity relation, but RR Lyrae do not.

Question 18

Massive stars synthesize chemical elements going from helium up to iron

A) throughout the entire interior.
B) primarily at across the entire surface.
C) only in the core of the star.
D) along the equator of the star.
E) in a shell with a radius that is half that of the star's total radius.

Question 19

The energy released during the process of nuclear fusion comes from

A) the change in nuclear binding energy.
B) the electric (Coulomb) force.
C) the gravitational attraction between protons and neutrons.
D) the absorption of neutrinos.
E) the formation of gravity waves.

Question 20

If a 25 M_SUN main-sequence star loses mass at an average rate of 10^-6 M_SUN/yr while on the main sequence, then how much mass will it lose in its lifetime of about 7 million years?

A) 3 M_SUN
B) 5 M_SUN
C) 7 M_SUN
D) 10 M_SUN
E) 12 M_SUN

Question 21

Type Ia and Type II supernovae are respectively caused by what types of stars?

A) white dwarfs; Cepheid variables
B) white dwarfs; pulsars
C) massive stars; white dwarfs
D) massive stars; neutron stars
E) white dwarfs; massive stars

Question 22

Type I and Type II supernovae can be distinguished by what combination of observations?

A) light curves and the detection of energetic cosmic rays
B) light curves and the detection of neutrons
C) light curves and the detection of radio pulses
D) spectra and light curves
E) spectra and X-ray emission

Question 23

The collapse of the core of a high-mass star at the end of its life lasts approximately

A) 1 second.
B) 1 minute.
C) 1 hour.
D) 1 week.
E) 1 year.

Question 24

Astronomers know they've found evidence of a past Type II supernova when they find

A) large numbers of cosmic rays.
B) a red supergiant star.
C) dark, light-absorbing clouds obscuring background stars.
D) an expanding cloud of hot gas surrounding a neutron star.
E) a white dwarf star.

Question 25

The Type II supernova that created the Crab Nebula was seen by Chinese and Arab astronomers in the year 1054 CE..Assuming that the nebula is about 6,500 light-years from us, we know the star must have exploded approximately in the year

A) 554 CE.
B) 1054 CE.
C) 1054 BCE.
D) 5447 BCE.
E) 7555 BCE.

Question 26

Massive stars explode soon after fusion to iron begins because

A) iron has the smallest binding energy of all elements.
B) neutrinos emitted during the fusion to iron are captured by the star's lighter elements.
C) fusion of elements heavier than iron requires energy, so the star runs out of fuel and cannot hold itself up against gravity.
D) stars do not contain elements heavier than iron; these are made in supernovae explosions.
E) iron nuclei are unstable and rapidly break apart into lighter elements.

Question 27

Supernovae are very energetic events.Of the following events, which is the brightest that a supernova can outshine at their maximum?

A) our entire Milky Way galaxy
B) an entire globular cluster of stars
C) the high-mass star Eta Carinae
D) a 1,000 R_SUN red supergiant star
E) a 50-day-period classical Cepheid

Question 28

In their post-main-sequence stages of evolution high-mass stars spend progressively shorter periods in each stage, in part because

A) they are losing energy faster as neutrino cooling becomes more important.
B) stellar cores become permanently inert once the stars leaves the main sequence.
C) the stars switch from fusion to fission to produce energy.
D) massive stars lose most of their nuclear fuel through powerful stellar winds.
E) the energy is now produced only via violent gravitational contractions.

Question 29

Which of the following is the correct order for elements fused (as fuel) in the core of late-stage high-mass stars?

A) hydrogen, helium, iron, carbon, silver, gold
B) carbon, oxygen, iron
C) helium, carbon, silicon, iron, gold
D) hydrogen, helium, carbon, neon, oxygen, silicon
E) hydrogen, helium, lithium, beryllium

Question 30

Once silicon burning initiates in the core of a high-mass star, the star has only a few ________ left to live.

A) seconds
B) days
C) months
D) years
E) million years

Question 31

Massive stars explode when they

A) accrete mass from their binary star companion.
B) generate uranium in their cores.
C) merge with another massive star.
D) run out of useful nuclear fuel in their core, and the cores collapse.
E) lose a lot of mass in a stellar wind.

Question 32

A few hours before a high-mass star will blast its outer layers in a colossal explosion, specialized detectors on Earth would recognize a spike in the number of

A) iron nuclei.
B) carbon nuclei.
C) protons.
D) neutrinos.
E) aurorae.

Question 33

The stellar energy is carried away primarily in the form of neutrinos when

A) an iron core builds up.
B) carbon burning begins.
C) stars are on the main sequence.
D) stars become unstable and pulsate.
E) stars acquire mass from close companions.

Question 34

The luminosity of a Type II supernova ________ with time.

A) increases only
B) decreases only
C) first increases, then decreases
D) first decreases, then increases
E) is a constant value

Question 35

A ⁴He atom has a binding energy of around 6.8 * 10¹⁴ joules (J) per kilogram (kg).If a single ⁴He atom has a mass of 6.6 *10 ^{- 27} kg, what is the binding energy of a single ⁴He atom?

A) 4.5 *10 ^{- 12} J
B) 1.6 *10 ^{- 19} J
C) 6.8 *10 ^{- 27} J
D) 4,184 J
E) 0 J

Question 36

Where did the iron in your blood come from?

A) Nuclear reactions on the surfaces of neutron stars
B) Nuclear reactions that took place in supernova explosions
C) Nuclear reactions in the cores of low-mass stars
D) Nuclear reactions in the cores of massive stars
E) Nuclear reactions in red giant and horizontal branch stars

Question 37

When the core of a massive star collapses, a neutron star forms because

A) all the charged particles are ejected in the resulting explosion.
B) protons and electrons combine to make neutrons.
C) iron nuclei disintegrate into neutrons.
D) neutrinos escaping from the core carry away most of the electric charge.
E) the collapse releases a large number of protons, which soon decay into neutrons.

Question 38

The Crab Nebula is an important test of our ideas about supernova explosions because

A) people saw the supernova and later astronomers found a pulsar inside the nebula.
B) the system contains an X-ray binary.
C) the nebula is expanding slowly, as expected from mass-loss rates in massive stars.
D) the original star must have been like the Sun before it exploded.
E) astronomers observed the merger of the two stars.

Question 39

Why does the luminosity of a high-mass star remain nearly constant as the star burns elements heavier than helium in its core, even though it is producing millions of times more
Energy per second than it did on the main sequence?

A) Most of the energy is trapped in the core, increasing the core's temperature.
B) All of the extra energy goes into heating the shells of fusion surrounding the core.
C) Most of the energy is absorbed by the outer layers of the star, increasing the star's radius but leaving its luminosity unchanged.
D) Most of the energy is carried out of the star by escaping neutrinos.
E) All of the energy goes into breaking apart light elements such as helium and carbon.

Question 40

During the main-sequence evolution of a massive star, progressively more massive elements are fused in the core until the core is filled with

A) carbon.
B) iron.
C) helium.
D) gold.
E) uranium.

Question 41

A neutron star in a mass-transfer binary system is called

A) a quasar.
B) a double star.
C) an X-ray binary.
D) a Cepheid variable.
E) a white dwarf star.

Question 42

One reason why we think neutron stars were formed in supernova explosions is that

A) all supernova remnants contain pulsars.
B) pulsars are made of heavy elements, such as those produced in supernova explosions.
C) pulsars are often found near Cepheids and Wolf-Rayet stars, which are also signs of massive star formation.
D) pulsars spin very rapidly, as did the massive star just before it exploded.
E) pulsars sometimes have material around them that looks like the ejecta from supernovae.

Question 43

What mechanism provides the internal pressure inside a neutron star?

A) ordinary pressure from hydrogen and helium gas
B) degeneracy pressure from neutrons
C) degeneracy pressure from electrons
D) rapid rotation
E) strong magnetic fields

Question 44

A neutron star contains a mass of up to 2 M_SUN in a sphere with a diameter approximately the size of

A) an atomic nucleus.
B) an apple.
C) a school bus.
D) a small city.
E) Earth.

Question 45

What is the reason for the very fast rotation of neutron stars?

A) It is a consequence of the conservation of angular momentum applied to collapsing objects.
B) The convection in the cores of high-mass stars is responsible for this.
C) The high temperature in the cores of high-mass stars imprints fast rotations.
D) The degenerate iron core leads to fast spins.
E) The fast rotation is due to their huge gravity on their surface.

Question 46

What characteristic of a star cluster is used to determine its age?

A) the chemical composition of stars in the cluster
B) the luminosity of the faintest stars in the cluster
C) the color of the main-sequence turnoff in the cluster
D) the total number of stars in the cluster
E) the apparent diameter of the cluster

Question 47

In a rescaled model in which the Crab Nebula (10 light-years across in reality) would only be about 10 km across, how big would the central neutron star (about 10 km in reality) be?

A) the size of football field
B) the size of an aspirin
C) the size of a football
D) the size of an atom
E) the size of the tip of a ballpoint pen

Question 48

List the H-R diagrams in the figure shown below from oldest to youngest.

A) 2, 1, 3, 4
B) 1, 4, 3, 2
C) 4, 3, 1, 2
D) 1, 2, 4, 3
E) 3, 1, 4, 2

Question 49

Which of the following is a common characteristic of a neutron star?

A) high luminosity
B) enormous magnetic field
C) low density
D) large radius
E) low temperature

Question 50

If the core of a high-mass star remains at the center of a Type II supernova remnant, that core will be classified as a(n)

A) white dwarf.
B) asymptotic giant branch (AGB) star.
C) main-sequence star.
D) blue horizontal branch star.
E) neutron star.

Question 51

What is the characteristic observational signal produced by a pulsar?

A) a faint, steady glow of infrared light
B) regularly timed pulses of light
C) semiregular novae
D) bursts of X-rays at irregular intervals
E) a single burst of gamma rays

Question 52

We can identify only a fraction of all the radio pulsars that exist in our galaxy because

A) gas and dust efficiently block radio photons.
B) few swing their beam of synchrotron emission in our direction.
C) most have evolved to become black holes, which emit no light.
D) massive stars are very rare.
E) neutron stars have tiny radii and are hard to detect even with large telescopes.

Question 53

Short gamma-ray bursts (GRBs) are most likely caused by

A) merging neutron stars.
B) high-mass main-sequence stars just beginning to fuse hydrogen in their cores.
C) the CNO cycle.
D) the oxygen-fusion phase of a high-mass star.
E) the triple-alpha process.

Question 54

Neutron stars have masses that range from

A) 3.5 M_SUN to 25 M_SUN.
B) 1.2 M_SUN to 30 M_SUN.
C) 2.5 M_SUN to 10 M_SUN.
D) 1.4 M_SUN to 2 M_SUN.
E) 0.1 M_SUN to 1.4 M_SUN.

Question 55

You observe three different star clusters and find that the main-sequence turnoff stars in Cluster 1 have spectral type F, the main-sequence turnoff stars in Cluster 2 have spectral type A, and the main-sequence turnoff stars in Cluster 3 have spectral type G.Which star cluster is the youngest and which one is the oldest?

A) Cluster 1 is the youngest and Cluster 2 is the oldest.
B) Cluster 2 is the youngest and Cluster 1 is the oldest.
C) Cluster 2 is the youngest and Cluster 3 is the oldest.
D) Cluster 3 is the youngest and Cluster 1 is the oldest.
E) Cluster 3 is the youngest and Cluster 2 is the oldest.

Question 56

Essentially all the elements heavier than iron in our Milky Way were formed

A) by supernovae or neutron star mergers.
B) during the formation of black holes.
C) by fusion in the cores of the most massive main-sequence stars.
D) during the formation of planetary nebulae.
E) during the initial stages of the Big Bang.

Question 57

The particles that circle the magnetic-field lines of neutron stars producing radiation are

A) neutrinos.
B) ions.
C) electrons and positrons.
D) neutrons.
E) photons.

Question 58

The weight of an average human of 70 kg on a typical 1.5 M_SUN, 10-km-wide neutron star would be about ________ times greater than here on Earth.

A) 10²⁷
B) 10¹²
C) 10⁵
D) 10
E) 10¹⁸

Question 59

Using the formula g =GM_NS/R²_NS, calculate the acceleration of gravity on a 2 M_SUN neutron with a radius of 10 km, and express this in terms of the acceleration of gravity on the surface
Of Earth (g = 9.8 m/s²).

A) 2.5 *10⁴
B) 2.5 *10⁵
C) 2.5 * 10⁸
D) 2.5 * 10¹¹
E) 2.5 * 10¹⁴

Question 60

Iron has 26 protons in its nucleus, and gold has 79 protons.Where did all the gold on Earth come from?

A) nucleosynthesis on the edges of black holes
B) nucleosynthesis that took place in supernova explosions
C) nucleosynthesis in the cores of low-mass stars
D) nucleosynthesis in the cores of massive stars
E) nucleosynthesis in red giant and horizontal branch stars

Question 61

Which of the following arguments would render the discovery of a 100 M_SUN star with less than 0.5 percent massive elements most intriguing?

A) Such high-mass stars shine mostly in the UV domain of the spectrum.
B) Young stars typically have much higher massive-element abundances than older stars.
C) Stars of such high mass very rarely form within interstellar clouds.
D) Stars like this one are most likely found in open clusters.
E) It would be the first star of such mass ever discovered.

Question 62

What is the meaning of nuclear binding energy?

Question 63

In young clusters the light is dominated by

A) luminous hot, blue, and some red supergiants.
B) luminous red giants and red dwarfs.
C) numerous Sun-like stars.
D) large numbers of protostars.
E) accreting white dwarfs.

Question 64

How do astronomers know that the Sun (and our Solar System) formed from the remnants of other stars?

A) The Sun acts like a low-mass star and a high-mass star at the same time.
B) Elements heavier than hydrogen and helium must have formed within other stars and then were ejected into space by supernovae.
C) Radioactive carbon could only form in the core of a high-mass star.
D) Jupiter shows signs of having been a main-sequence star at one point.
E) Evidence shows that the asteroids and comets must have formed around stars with different spectral types than the Sun.

Question 65

Which of the clusters in the figure shown below are open clusters?

A) NGC 290 and M53
B) NGC 290 and M55
C) NGC 290 and NGC 6530
D) M53 and M55
E) M53 and NGC 290

Question 66

In the figure shown below, the H-R diagram for the very old cluster M55 shows the presence of an intriguing type of object, namely main-sequence stars bluer and more luminous than the turnoff stars.These stars have been called "blue stragglers," and an attractive explanation might be that they are

A) newly formed stars within in the very gas-rich globular cluster environment.
B) high-mass stars, recently formed by mergers of old, lower-mass stars in the densely packed cluster.
C) very luminous Type Ia supernovae at their peak luminosity.
D) exotic stars that produce energy by mechanisms other than nuclear fusion.
E) stars that do not belong to M55.

Question 67

Why do very massive stars collapse, causing them to explode, once they generate an iron core (hint: see figure below)?

Question 68

Recent research revealed that stars like our Sun slow their rotation as they age while on the main sequence.Assuming that you find a nearby Sun-like star with a measured rotational period of only 4-5 days, it is likely that, compared with our Sun, the star will have

A) a higher abundance of massive elements.
B) a very blue color.
C) a much smaller size.
D) no planets around it.
E) very weak gravity.

Question 69

How do Classical Cepheid variable stars differ from RR Lyrae variable stars in their masses, luminosities, and periods?

Question 70

The figure below shows the H-R diagram for the very young cluster NGC 6530.Notice that the main sequence is missing the low-luminosity red tail.At the same time, there are several reddish and yellowish objects to the right of the main sequence (clearly marked).What could these objects represent?

A) evolved Sun-like stars
B) planets orbiting other stars
C) red dwarfs
D) red supergiants
E) protostars in the pre-main-sequence stages

Question 71

A H-R diagram is made for two star clusters, Cluster A and Cluster B.Cluster A has stars of spectral type A, while Cluster B has no such stars.What can we conclude about these two clusters from this information?

A) Cluster A has more total stars than Cluster B.
B) Cluster A is more distant than Cluster B.
C) Cluster A has less iron present than Cluster B.
D) Cluster A is younger than Cluster B.
E) Nothing can be determined without more information.

Question 72

How does convection in the core of a high-mass star affect the star's main-sequence lifespan?

Question 73

Why is the CNO cycle the primary fusion cycle in only high-mass stars?

Question 74

What provides us the best clues as to the age of a galaxy like ours?

A) the periods of the fastest-spinning pulsars and Cepheid variables
B) the number of planetary nebulae
C) the observed frequency of high-mass-star supernovae
D) the H-R diagrams of globular clusters of stars
E) the luminosity of the most massive stars

Question 75

The figure below shows three distinct types of pulsating stars: Type I (Classical) Cepheids, type II Cepheids and RR Lyrae.Assume that you find a variable star whose period of pulsation is several days.You accurately measure its apparent brightness, but you misidentify its type, labeling it "Classical" instead of Type II, which would in fact be its correct type.What would be the effect in the determination of distance?

Question 76

What should be true about the oldest stars in the Milky Way?

A) They would have lots of heavy elements because they have been around for a long time and have undergone a lot of nucleosynthesis in their cores.
B) They would be seen as supergiants.
C) They would have few heavy elements because there was not much chance for earlier generations of stars to explode as supernovae before these stars were formed.
D) They would be massive because they were among the first stars formed.
E) They would likely be seen as pulsars.

Question 77

Betelgeuse is a star whose luminosity exceeds 1.2 * 10⁵ L_SUN, but its measured surface temperature is quite low for a star, about 3500K.What would be its estimated size and where would it fall in the H-R diagram shown in the figure below? What would be the final fate of Betelgeuse?

Question 78

Why do main-sequence high-mass stars lose so much mass compared with low-mass stars?

Question 79

With the Hubble Space Telescope, you discover a Cepheid variable star in a nearby galaxy that has a period of 30 days.If nearby Cepheids follow a period-luminosity that relates the absolute magnitude to the period of pulsation via , where P(days) is the star's period in days, then what is this Cepheid's luminosity? Recall that the Sun's absolute magnitude is M = 4.83.If the apparent magnitude of the Cepheid is 25, what is this galaxy's distance in parsecs?

Question 80

At what rate would a 25 M_SUN star lose mass via stellar winds (in M_SUN/yr) in order to reduce its mass by 20 percent in its lifetime? The main-sequence lifespan is about 7 million years.