Deck 13: Evolution of High-Mass Stars

Question 1

Gravity is nothing more than a curvature in the fabric of spacetime.

Answer 1

True

Question 2

Most of the uranium (U; atomic mass = 238)found on the Earth was formed in Type II supernovae explosions.

Answer 2

True

Question 3

Special relativity says that moving clocks run slower.

Answer 3

True

Question 4

Gravitational lensing allows us to see distant objects that would otherwise be blocked by a star or galaxy.

Question 5

Einstein's special theory of relativity implies that if a person standing at the front of a train traveling at 0.1 km/s shines a flashlight out in front of the train,the emitted photons will travel at a speed of 300,000.1 km/s.

Question 6

The abundances of elements in the Crab Nebula (image below),like all planetary nebulae,show that it formed as the byproduct of fusion present in low-mass stars.

Question 7

Black holes emit no light whatsoever.

Question 8

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

A) age
B) rotation period
C) distance
D) mass

Question 9

Examine the figure below.Hydrogen burns through the CNO cycle only in high-mass main-sequence stars because of the greater __________ in their cores.

A) concentration of heavy elements like carbon
B) densities
C) abundance of hydrogen
D) temperatures

Question 10

The production of large numbers of neutrons in nuclear reactions at the core of a massive star helps rob the core of energy and speeds its eventual collapse.

Question 11

The densest state of matter found in nature occurs inside a white dwarf star.

Question 12

High-mass stars differ from low-mass stars in that they burn helium to carbon when on the main sequence.

Question 13

Black holes have an infinitely small radius,but a finite event horizon.

Question 14

Fusion reactions that create chemical elements heavier than oxygen require energy input,thus these reactions cannot provide a star with power.

Question 15

Every pulsar is a neutron star,but not every neutron star is a pulsar.

Question 16

An 8 M _$\bigodot$ star will eventually die as a Type Ia supernova.

Question 17

Type Ia and Type II supernovae are approximately equal in luminosity.

Question 18

All evolutionary differences between high- and low-mass stars can be attributed to differences in the amount of gravity each star possesses.

Question 19

Which of the stars from the figure below would show variability in its brightness?

A) Star A
B) Star B
C) Star C
D) Star D

Question 20

Pulsating variable stars are more commonly known as pulsars.

Question 21

Once silicon burning begins to fuse iron in the core of a high-mass main-sequence star,it only has a few __________ left to live.

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

Question 22

In the figure below,when elements from section A undergo fusion,energy is _______.Because of this fact,it would be ________ to find a high-mass main sequence star with a high concentration of elements from section B.

A) released; likely
B) absorbed; likely
C) released; unlikely
D) absorbed; unlikely

Question 23

What would happen if mass were continually added to a 2 M _$\bigodot$ neutron star?

A) The star's radius would increase.
B) The star would eventually become a black hole.
C) The star would erupt as a nova.
D) All of the above would occur.

Question 24

Once carbon begins burning in the core of a high-mass star,the outer layers begin to fall inward,driving up the fusion rates and speeding up the star's evolution primarily because:

A) the number of particles in the core is decreasing which now take up less space
B) most of the energy is now carried away from the core by escaping neutrinos which have few if any obstacles to leaving the star
C) carbon is a more stable element that appears to settle the star
D) the light given off by the fusion of carbon is a different wavelength than given off by previous reactions so the radiation pressure is much smaller

Question 25

Essentially all the elements heavier than iron in our galaxy were formed:

A) by supernovae
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

Question 26

Neutron stars have masses that range from:

A) 3.5 M _$\bigodot$ to 25 M _$\bigodot$
B) 1.2 M _$\bigodot$ to 30 M _$\bigodot$
C) 2.5 M _$\bigodot$ to 10 M _$\bigodot$
D) 1.4 M _$\bigodot$ to 3 M _$\bigodot$

Question 27

During the main-sequence evolution of a massive star,increasingly heavier elements are fused in the core,giving the core support for:

A) decreasingly shorter times
B) increasingly longer times
C) an approximately equal amount of time
D) approximately 10,000 years

Question 28

What is the minimum mass main-sequence star that becomes a Type II supernova?

A) 4 M _$\bigodot$
B) 8 M _$\bigodot$
C) 12 M _$\bigodot$
D) 25 M _$\bigodot$

Question 29

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) roughly horizontal path
D) None of the above answers is correct.

Question 30

A neutron star contains a mass of up to 3 M _$\bigodot$ in a sphere with a diameter approximately the size of:

A) an atomic nucleus
B) a school bus
C) a city
D) the Earth

Question 31

The main difference between Cepheid variable stars and RR Lyrae stars is:

A) their pulsation mechanisms
B) their masses
C) that Cepheids form at much greater distances from Earth
D) that RR Lyrae were discovered much earlier than Cepheids

Question 32

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

A) one second
B) one hour
C) one week
D) one year

Question 33

Why does the luminosity of a high-mass star remain nearly constant as the star burns heavy elements 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.

Question 34

Which of the following is NOT a common characteristic of a neutron star?

A) Extremely high density
B) Enormous magnetic field
C) Very short rotation period
D) All of these are common characteristics of a neutron star.

Question 35

The Type II supernova that created the Crab Nebula (image below)was seen by Chinese and Arab astronomers in the year A.D.1054 Because the star is 6,500 light-years away from us,we know the star exploded in the year:

A) A.D.7554
B) A.D.1054
C) 5446 B.C.
D) 7554 B.C.

Question 36

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

A) iron has poor nuclear binding energy
B) iron cannot fuse with other nuclei to produce energy
C) iron supplies too much pressure
D) iron fusion only occurs in a degenerate core

Question 37

A Cepheid star varies in luminosity because:

A) the entire star pulsates from its core to its surface
B) the outer envelope of the star pulsates
C) the star rotates too quickly
D) the star is too massive to be stable

Question 38

If a 25 M _$\bigodot$ main-sequence star loses mass at a rate of 10^-6 M _$\bigodot$ /yr then how much mass will it lose in its 3-million-year lifetime?

A) 3 M _$\bigodot$
B) 5 M _$\bigodot$
C) 8 M _$\bigodot$
D) 12 M _$\bigodot$

Question 39

We can identify only a small fraction of all the 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

Question 40

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 minimize electromagnetic forces
C) iron nuclei disintegrate into neutrons
D) neutrinos escaping from the core carry away most of the electromagnetic charge

Question 41

__________ is the result of mass distorting the fabric of spacetime.

A) Energy
B) Radiation
C) Fusion
D) Gravity

Question 42

Hawking radiation is emitted by a black hole when:

A) the black hole rotates quickly
B) the black hole accretes material
C) a virtual pair of particles is created from the vacuum of space
D) synchrotron radiation is emitted by infalling charged particles

Question 43

Normally muons created by cosmic rays at high altitudes decay in a very short time,a time so short that they should not reach the ground.From the figure below,which muon is most likely to be detected on the ground?

A) Muon A
B) Muon B
C) Muon C
D) Muon D

Question 44

Why do large,high-mass main-sequence stars never become red giants?

Question 45

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

Question 46

The event horizon of a black hole is defined as:

A) the point of maximum gravity
B) the radius of the original neutron star before it became a black hole
C) the point at which shock waves emanate from the strong gravitational distortion the black hole creates in the fabric of spacetime
D) the radius at which the escape speed equals the speed of light

Question 47

Light is increasingly redshifted near a black hole because:

A) the photons are moving away from us very quickly as they are sucked into the black hole
B) the photons are moving increasingly faster in order to escape the pull of the black hole
C) time is moving increasingly slower in the observer's frame of reference
D) the curvature of spacetime is increasingly stretched near the black hole,which in turn stretches the wavelengths of the photons

Question 48

Black holes that are stellar remnants can be found by searching for:

A) dark regions at the centers of galaxies
B) variable X-ray sources
C) extremely luminous infrared objects
D) objects that emit very faint radio emission

Question 49

What are some ways that finding a Cepheid variable star is significant?

Question 50

The equivalence principle says that:

A) being stationary in a gravitational field is the same as being in an accelerated reference frame
B) the universe is homogeneous and isotropic
C) at any radius inside a star the outward gas pressure must balance the weight of the material on top
D) mass and energy are interchangeable and neither can be destroyed

Question 51

If an 8 M _$\bigodot$ star loses mass at an average rate of 10^-6 M _$\bigodot$ /yr in a stellar wind,how many years would it take for its mass to be reduced to 6 M _$\bigodot$ ? Would this amount of mass loss be possible in the star's lifetime?

Question 52

Which of the following is a consequence of Einstein's special theory of relativity?

A) Moving clocks run quicker.
B) The velocity of light depends on the speed of the observer.
C) Distances appear shorter when traveling near the speed of light.
D) Gravity arises because mass distorts spacetime.

Question 53

If the Earth were to be condensed down in size until it became a black hole,its Schwarzschild radius would be:

A) 1 cm
B) 1 m
C) 1 km
D) 10 km

Question 54

Assume that a group of explorers traveled to the Orion Nebula,the nearest star-forming cloud at a distance of 1,300 light-years,using revolutionary technology that allowed them to travel at a speed very close to the speed of light.Observers back on Earth would say it took them __________ to get there,but the travelers would say it took them __________ to get there.

A) slightly more than 1,300 years; much less than 1,300 years
B) slightly more than 1,300 years; slightly less than 1,300 years
C) slightly less than 1,300 years; slightly more than 1,300 years
D) exactly 1,300 years; much less than 1,300 years

Question 55

If the Sun were to be instantly replaced by a 1 M _$\bigodot$ black hole,the gravitational pull of the black hole on Earth would be:

A) much greater than it is now
B) the same as it is now
C) much smaller than it is now
D) irrelevant because Earth would be quickly obliterated by the strong tidal force of the black hole

Question 56

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

Question 57

An indestructible robot would feel __________ as it crossed the event horizon of a black hole.

A) incredibly strong tidal forces
B) intense heating
C) intense gravitational stretching
D) nothing

Question 58

Gravitational lensing occurs when __________ distorts the fabric of spacetime.

A) a star
B) dark matter
C) a black hole
D) any massive object

Question 59

While traveling the galaxy in a spacecraft,you and a colleague set out to investigate the 10⁶ M _$\bigodot$ black hole at the center of our galaxy.Your colleague hops aboard an escape pod and drops into a circular orbit around the black hole,maintaining a distance of 1 AU,while you remain much farther away in the spacecraft but from which you can easily monitor your colleague.After doing some experiments to measure the strength of gravity,your colleague signals his/her results back to you using a green laser.What would you see?

A) His/her signals,because he/she is orbiting well outside the event horizon.
B) His/her signals,but shifted to a much redder wavelength because he/she is very close to the event horizon.
C) Nothing,because your colleague has crossed the event horizon.
D) Nothing,because no light can escape the gravitational pull of a black hole no matter how close he/she is to it.

Question 60

Photons have no mass,and Einstein's theory of general relativity says:

A) their paths through spacetime are curved in the presence of a massive body
B) their apparent speeds depend on the observer's frame of reference
C) they should not be attracted to a massive object
D) their wavelengths must remain the same as they travel through spacetime

Question 61

Examine the figure below.Explain what the equivalence principle is in general relativity.

Question 62

Galileo supposedly experimented with gravity by dropping two objects of different masses from the leaning tower of Pisa at the same instant and observing that they hit the ground at the same time.If Albert Einstein had done the experiment,how would his conclusion have differed from Galileo's?

Question 63

Examine the figure of a pulsar below.What are pulsars,and what circumstance must the Earth be in for astronomers to observe one?

Question 64

What is the difference between the singularity and the event horizon of a black hole?

Question 65

The figure below shows the relative abundances of different elements on Earth.Explain why elements less massive than iron are,in general,most common,why there is a small peak at Iron,and why elements more massive than iron are less common.

Question 66

Normally muons created by cosmic rays at high altitudes decay in a very short time,a time so short that they should not reach the ground.From the figure below,why does increasing speed of muons created by cosmic rays at high altitudes mean that additional muons will reach the ground before decaying?

Question 67

Explain why Einstein's theory of general relativity predicts the existence of gravitational lensing.

Question 68

Although a Type II supernova shines with a luminosity of 100 billion L _$\bigodot$ ,most of the energy in the explosion is emitted in another way.What is it,and how much more energy does it carry compared to the light?

Question 69

In comparison,the main-sequence lifetime of the star is just less than 81 million years (Table 12.1).Therefore,the star could lose this much mass because its main-sequence lifetime is much longer than the time it would take to do so.

Name at least two processes that speed the collapse of the core of a dying high-mass star.

Question 70

Which has a smaller radius,a 2 M _$\bigodot$ neutron star or a 3 M _$\bigodot$ neutron star? What supports each of these stars from collapsing to form a black hole?

Question 71

While traveling the galaxy in a spacecraft,you and a colleague set out to investigate a 1 M _$\bigodot$ black hole.Your colleague hops aboard an escape pod and drops into a circular orbit around the black hole maintaining a distance of 10 km from it,while you remain much farther away inside the spacecraft.After doing some experiments to measure the strength of gravity,your colleague signals the results back to you using a green laser.What would you see,and why?